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Physicochemical and rheological properties of cross-linked inulin with different degree of polymerization
Accepted Manuscript Physicochemical and rheological properties of cross-linked inulin with different degree of polymerization Yao Li, Xiaohan Ma, Xiong Liu PII:
S0268-005X(18)31606-0
DOI:
https://doi.org/10.1016/j.foodhyd.2018.11.026
Reference:
FOOHYD 4767
To appear in:
Food Hydrocolloids
Received Date: 22 August 2018 Revised Date:
15 October 2018
Accepted Date: 12 November 2018
Please cite this article as: Li, Y., Ma, X., Liu, X., Physicochemical and rheological properties of cross-linked inulin with different degree of polymerization, Food Hydrocolloids (2018), doi: https:// doi.org/10.1016/j.foodhyd.2018.11.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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ACCEPTED MANUSCRIPT Physicochemical and rheological properties of cross-linked inulin
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with different degree of polymerization
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Yao Li, Xiaohan Ma, Xiong Liu*
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College of Food Science, Southwest University, Chongqing, 400715, China
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* Corresponding author: Xiong Liu
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Address: No. 2 Tiansheng Road, Beibei District, Chongqing, 400715, P. R. China
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Tel: +86-23-68250375
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Fax: +86-23-68251947
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E-mail: [email protected] (X. Liu)
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ACCEPTED MANUSCRIPT Abstract: Long-chain inulin (L-In) and short-chain inulin (S-In) from native inulin
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was separated through the method of alcohol precipitation. Cross-linked inulin with
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two different degree of polymerization (average DP = 6.88 and 15.10) were prepared
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in aqueous solutions by using the L-In and S-In respectively as raw material and
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sodium hexametaphosphate as cross-linker. Structural characteristics of cross-linked
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inulin were determined by Fourier-transform infrared spectroscopy and scanning
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electron microscopy. Compared with native L-In and S-In, cross-linked inulin had a
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higher intrinsic viscosity, stronger stability and moisture absorption capability, but
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lower water solubility. Only 1% reducing sugar produced when cross-linked inulin
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was heated within 100 °C, and inulin hydrolysis occurred in acidic environment (pH <
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6). Rheological properties of inulin dispersions with different degree of
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polymerization were investigated and compared. The viscoelastic properties of steady
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shear measurements indicated that cross-linked inulin dispersions presented
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shear-thinning behaviors, which could be described by a power law model with
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determination coefficients (R2 = 0.9312~0.9926). The viscoelastic properties of
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dynamic frequency sweep measurements indicated that cross-linked inulin dispersion
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showed more solid viscoelastic properties than corresponding native inulin
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dispersions.
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Keywords: cross-linked; inulin; polymerization degree; physicochemical property;
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rheological property.
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1. Introduction Prebiotics are substrates selectively utilized by host microorganisms conferring a
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health benefit (Gibson et al., 2017). Inulin, known as a rising attractive prebiotic, is
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composed of D-furan fructose units and one terminal glucose unit, exhibiting many
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beneficial physiological functions, such as antioxidant activity, ability to improve
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colonic microbiota, promote mineral absorption, regulate blood glucose and blood
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lipids (Balthazar et al., 2018a; Shoaib et al., 2016). Ranging from 2 to 60
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monosaccharide units, the degree of polymerization (DP) of natural inulin have an
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effect on the physicochemical properties of inulin (Barclay, Ginicmarkovic, Cooper,
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& Petrovsky, 2010). Generally, short-chain inulin can contribute to an improved
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mouth feel due to good solubility and mild sweetness, and long-chain inulin can act as
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fat replacer or texture modifier due to its poor solubility and good viscosity stability.
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Based on nutritional and physicochemical properties, inulin has been widely used in
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an increasing number of applications throughout the food production. The prebiotic
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inulin have proven to be a promising fat substitute and to improve the functional
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potential in sheep milk ice cream formulation (Balthazar et al., 2017; Balthazar et al.,
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2018b); the use of inulin could be used for prebiotic in the formulation of whey
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beverage (Guimaraes et al., 2018a). Besides, the use of inulin for prebiotic in
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probiotic yogurt could enhance the viability of lactobacillus during storage (Canbulat
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& Ozcan, 2015).
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ACCEPTED MANUSCRIPT However, native inulin may induce a disadvantageous rapid renal excretion due to
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its low molecular weights (Mw). Cross-linking of inulin to enhance its Mw is a
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strategy to avoid this disadvantage (Li, Hu, Chen, Zheng, Liu, & Ma, et al. 2010).
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Currently, there have been some reports on the synthesis methods of cross-linked
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inulin. For example, García synthesized cross-linked inulin using phosphoryl chloride
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as the cross-linker under alkaline condition (García, Vergara, & Robert, 2015); the
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cross-linked inulin was prepared by Li’s method using epichlorohydrin as the
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cross-linker to conjoin inulin molecules (Li et al., 2010); on the other hand, Vervoort
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synthesized cross-linked inulin with glycidyl methacrylate to introduce double bonds
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in a radical polymerization (Vervoort et al., 1997). These present methods for
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preparation of cross-linked inulin feature various disadvantages, such as long
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preparation time, high toxicity of cross-linker and violent reaction conditions.
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Therefore, a novel method for cross-linked inulin with advantages, such as gentle
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reaction condition, time saving, absence of side-effect and simple operation is
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desirable. Moreover, in those reported works, native inulin (a mixture of long-chain
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and short-chain inulin) was cross-linked immediately without classification before
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crosslinking, resulting in the variable DP of cross-linked inulin leading to weak
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compatibility and instability. Therefore, systematic research on physicochemical and
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rheological properties of cross-linked inulin with different DP is lacking which limit
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the deeper-level analysis and application of inulin in the food production.
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This study aimed to develop a commercially novel method for preparation of 4
ACCEPTED MANUSCRIPT cross-linked inulin for potential industrial application and to evaluate the
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physicochemical and rheological properties of cross-linked inulin with different DP.
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2. Materials and methods
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2.1. Materials
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Native inulin (average DP < 10) was supplied by Xi’an Ruiling Technology Co.,
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Ltd. (Xi’an, China). Anhydrous ethanol, sodium hexametaphosphate (SH), anhydrous
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sodium carbonate, hydrochloric acid, sulfuric acid, nitric acid, hydroquinone, standard
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polyethylene glycols, 3,5-dinitrosalicylic acid and phenol were purchased from
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Kelong Chemical Reagent Factory (Chengdu, China). All reagents were of analytical
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grade.
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2.2 Preparation of cross-linked inulin
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16 g of native inulin was added to 80 mL distilled water at room temperature and
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gently stirred until dissolved. Then 20 mL of anhydrous ethanol was added into the
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solution. The mixture solution was stored at 4 °C for 24 hours. Then sediment and
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liquid supernatant were separated by centrifugation. After lyophilizing for sediment,
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long-chain inulin (L-In) in native inulin was obtained. After condensation and
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lyophilizing for liquid supernatant, short chain inulin (S-In) were obtained.
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Cross-linked inulin was prepared via a method similar to that of starch modification
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(Ren, Jiang, Wang, Zhou, & Tong, 2012; Liu, Dong, Men, Jiang, Tong, & Zhou, 2012). 5
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at 25 °C and then 1.1 g of cross-linker SH was added followed by the addition of
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Na2CO3 (2 mol/L) until reached pH 10. Then the pre-polymerization solution was
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polymerized with continuous stirring at 45 °C for 3.5 h. Upon completion of the
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reaction, the pH of the suspension was adjusted to 7 with 2 mol/L HCl. Then
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cross-linked inulin was precipitated with 95% ethanol, followed by centrifugation and
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washing with anhydrous ethanol. Finally, after washings with water and lyophilizing,
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cross-linked long-chain inulin (CL-In) was obtained. Cross-linked short-chain inulin
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(CS-In) was prepared in the same manner but with the S-In in place of L-In.
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2.3 Structure characterization
Different inulin (L-In, S-In, CS-In and CL-In) were characterized by FT-IR
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(Equinox 55, China), the scanning range was from 400 cm−1 to 4000 cm−1. SEM
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analysis was performed by a scanning electron microscope (Sigma 300, Carl Zeiss
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Jena) with amplification at 10
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were sputter-coated with gold before analysis.
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2.4 Determination of inulin content
times (Palma, García, & Márquez, 2014); samples
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Inulin is a non-reducing polysaccharide, glucose and fructose contained in native
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inulin are reducing sugars. Total sugar content was determined by method of
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phenol-sulfuric acid, reducing sugar content was determined by the dinitrosalicylic
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acid (DNS) method (Miller, 1959). Ultraviolet and visible spectrophotometer 6
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to get the inulin content accurately, the reducing sugar content contained in native
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inulin was subtracted (Glibowski & Bukowska, 2011).
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W=
ρ-ρ1 ×V m
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Where W is the inulin content in sample (%), ρ refers to the mass concentration of
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total sugar (mg/mL), ρ1 stands for the mass concentration of reducing sugars (mg/mL),
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V is the volume of the sample (mL), and m represents the amount of sample (mg).
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2.5 Determination for degree of polymerization
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Molecular weights (Mw) of different inulin (L-In, S-In, CS-In and CL-In) were
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determined by a high performance gel-filtration chromatography (HPGFC), which
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was performed on a high-performance liquid chromatography system (Agilent 1260,
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Germany) with a TSK-GEL GMPWXL column (7.8 × 300 mm) eluted with pure
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water at a flow fate of 0.7 mL/min (Zhang, Tian, Jiang, & Ming, 2014). Standard
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polyethylene glycols (600 Da, 1000 Da, 2000 Da, 4000Da, 10000 Da) were also
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applied to the same system. The molecular weight distributions of the samples were
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determined by comparison with the retention time of standard polyethylene glycols
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under the same conditions. The DP of inulin can be obtained according to Mw = 162
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DP + 180.
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2.6 Determination of solubility, viscosity, and stability
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2.6.1 Water Solubility
The solubility experiments were visually conducted in an illuminated condition in a
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thermostatic water bath. Water solubility of different inulin (L-In, S-In, CS-In and
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CL-In) were evaluated with 100 mL water in a beaker, which was then immersed in a
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water bath at 25 °C, 40 °C, 60 °C and 80 °C, respectively (Wang, Fu, & Yang, 2012;
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Naskar, Dan, Ghosh, & Moulik, 2010). The temperature was controlled by
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temperature regulator and water circulator in the experiment. Inulin and water mixture
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was stirred at 150 rpm to make the solution homogeneous. At each temperature, 0.1 g
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of inulin was added to water solution at a slow speed rate of 0.1 g/min until
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undissolved particles appeared in the solution. After equilibrium, stirring was
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discontinued and the solution was settled in water bath at the appropriate temperature
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for 1 h. Finally, the upper portion was collected, filtered, poured into a volumetric
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flask, and diluted to an appropriate concentration for content analysis.
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2.6.2 Intrinsic viscosity measurement
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With pure water as blank sample, an Ubbelohde viscometer (Ф0.57 mm - 4 mL)
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was applied to measure intrinsic viscosity of different inulin samples (L-In, S-In,
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CS-In and CL-In) at 25 °C. The flow time of a solution in the viscometer was taken
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after thermal equilibrium allowing 15 min time for each solution prior to
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measurement (Naskar, Dan, Ghosh, & Moulik, 2010).
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2.6.3 Thermal and acid stability
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stability (Glibowski & Bukowska, 2008). Reducing sugar content was determined
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through the dinitrosalicylic acid (DNS) method (Miller, 1959). Thermal stability tests
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were implemented using 20 mL of 10 mg/g different sample solution (L-In, S-In,
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CS-In and CL-In) immersed in water bath at 20, 40, 60, 70, 80, 100 °C for 1 h.
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Acid stability tests were implemented by adjusting pH of sample solution to
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different standard (1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0) with hydrochloric acid at 25 °C.
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After hydrolysis for 1 h, pH of the sample solution was adjusted to 7.0. RRS (%) can
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directly reflect on the increment of reducing sugar share.
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(2)
Where, m1 is the reducing sugar content after 1h, m2 represents the reducing sugar
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RRS % =
content before 1h, M is the total sugar content.
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2.7 Moisture absorption and holding capability measurement
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Moisture absorption was measured through the method similar to Zhou’s (Zhou,
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Zhang, Ma, & Tong, 2008). Different samples (L-In, S-In, CS-In and CL-In) were
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stored at room temperature in Conway desiccators with controlled relative humidity
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maintained by saturated salt solutions ((NH4)2SO4, Na2CO3), and the corresponding
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humidity were 81%, and 92% RH at room temperature. Samples were fully dried at
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80 °C and weighted (Wd) before put into desiccators. A set of dried sample were put
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ACCEPTED MANUSCRIPT into desiccators with a given humidity. After stored in desiccators for predetermined
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time (6, 12, 24, 36, 48, and 60 h), samples were taken out and weighted (Ww). The
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moisture content (%) was determined by Equation (3) and moisture sorption kinetic
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curves were plotted.
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–
/
2.8 Rheological properties
(3)
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Moisture content % =
A rheometer (Discovery HR-2, TA Instruments Ltd., America) was used to
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determine the rheological properties of inulin suspension.
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2.8.1 Steady shear measurements
Different inulin (L-In, S-In, CS-In and CL-In) aqueous hydrocolloid dispersions
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were prepared through suspending in water at 25 °C at a concentration of 5 %, 10 %,
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20 %, 30 %, 40 %, 50 % (w/v) respectively and stored at 25 °C and used within 2
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days after the preparation. Inulin suspensions were loaded on the base plate and
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excessive sample was wiped off with a spatula. A thin layer of low-density silicone oil
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was covered on the periphery of geometry to minimize evaporation loss before
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measurement (Wang, Gu, Li, Hong, & Cheng, 2013). TA rheometer was used to
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determine the relationship between viscosity and shear rate. The measuring geometry
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employed was a parallel plate (40 mm in diameter). The gap size and testing
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temperature were set at 500 µm and 25 °C. A range of shear rate (1~500 s-1) was
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was tested at temperature ranging from 20 to 80 °C with a shear rate of 50 s-1 to
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investigate the effect of temperature on the steady rheological properties of inulin.
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2.8.2 Dynamic frequency sweep measurements
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A concentration of 40 % (w/v) for inulin aqueous hydrocolloid dispersions were
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used to investigate the dynamic rheological properties. Small-amplitude oscillatory
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shear experiments were conducted over a frequency (w) range of 1~100 rad/s at 25 °C,
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yielding the shear storage (G’) and loss (G’’) moduli. Strain value was set at 2 %,
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which was within its linear viscoelastic range (Freitas, Gorin, Neves, & Sierakowski,
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2003).
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2.9 Statistical analyses
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All experiments were conducted in triplicate for each sample, and results were
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expressed as mean ± standard deviation. All data were statistically compared between
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groups using one-way analysis of variance. Significant differences among the mean
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values were determined by Duncan’s multiple range test with p < 0.05.
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3. Results and discussion
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3.1 Structural characterization of different inulin
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FT-IR was employed to demonstrate successful cross-linking of inulin to ensure the
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increasing DP. Infrared spectra of CL-In (Fig. 1 (a)), L-In (Fig. 1 (b)), CS-In (Fig. 1 11
ACCEPTED MANUSCRIPT (c)) and S-In (Fig. 1 (d)) were registered and compared. As shown in Fig. 1, the
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spectra of L-In and S-In showed almost the same results just as CL-In and CS-In. The
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peak at 933 cm-1、1031 cm-1、3400 cm-1 represent skeleton absorption peaks of inulin.
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L-In displayed a stretching vibrational absorption peak of glycosidic bond at 1132 cm
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−1
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indicated by arrows. Besides, the stretching vibrational peak at 3200 ~ 3600cm
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CL-In was significantly weaker than that of L-In, indicating that hydroxyl was
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involved in nucleophilic substitution reaction. These results confirmed the successful
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crosslinking of inulin in this experiment.
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−1
as
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, and CL-In displayed relatively strong band of organic phosphate at 1280 cm
SEM was employed to characterize the morphologies of L-In, S-In, CS-In and
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CL-In. Fig. 2 showed that the morphology of S-In (Fig. 2(a)), L-In (Fig. 2(b)), CS-In
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(Fig. 2(c)) and CL-In (Fig. 2(d)) in SEM micrographs significantly differed after they
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were amplified by 10 3 times. SEM images showed that S-In (Fig. 2(a)) and L-In (Fig.
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2(b)) (Fig. 2(b)) were found to comprise relatively smooth microspheres. In contrast,
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CS-In (Fig. 2(c)) and CL-In (Fig. 2(d)) displayed significantly rougher and more
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uneven clusters of polymer rather beads. The size of L-In microspheres was obviously
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larger than that of S-In. Polymers of CS-In and CL-In were irregular in shape, with
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noticeable indentation and roughness on surface of polymers these shows the effect of
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inlet temperature and solvent on the morphology characteristics (García, Vega,
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Jimenez, Santos, & Robert, 2013). In addition, high viscosity of CL-In may cause the
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occurrence of adhesion between the polymers.
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3.2 Purity and molecular weight (Mw) of inulin Purity of S-In, L-In, CS-In and CL-In was evaluated by the method of 2.4, and as
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86.13±4.09 %, 90.91±2.77 %, 91.64±1.57 %, and 93.54±2.31 %, respectively. The
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purity of S-In was relatively lower than the others, due to the involvement of diffluent
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small molecular like reducing sugar. Furthermore, the HPGFC results indicated that
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the average molecular weights of S-In, L-In, CS-In and CL-In were 877, 2022, 1295
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and 2626 Da (shown in Table 1), respectively. S-In (average DP = 4.30) and L-In
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(average DP = 11.37) could be separated by alcohol precipitation, because inulin with
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small molecular weight had a better solubility in alcohol and had not been precipitated.
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The average molecular weight of CL-In was 2626 Da, more than that of L-In (2022
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Da), indicating that cross-linked inulin with greater molecular weight and higher DP
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than native inulin was obtained, which lies in the fact that small inulin molecules were
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cross-linked by cross-linker, leading to the formation of a larger inulin molecule.
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3.3 Solubility and intrinsic viscosity
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Solubility data for inulin in water at different temperatures are presented in Table 1.
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As can be observed, solubility at a particular temperature increases as: CL-In < L-In <
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CS-In < S-In, indicating that the solubility of inulin decreased significantly with the
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increase of inulin DP. Besides, with the temperature increasing, the solubility of inulin
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increased whereas the solubility increment of inulin with higher DP was obviously
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smaller.
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L-In < CL-In, indicating inulin with better intrinsic viscosity could be obtained
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through cross-linking. This could be explained by the increase of DP and introduction
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of hydrophilic phosphoric acid groups. With higher intrinsic viscosity, CL-In could be
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a potential food additive to improve food texture.
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3.4 Thermal and acid stability of inulin
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Thermal stability of S-In, L-In, CS-In and CL-In was investigated in temperature
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ranging from 20 °C to 100 °C. As shown in Fig. 3(a), the rising temperature within
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100 °C had significant effects on RRS (%). Besides, RRS (%) of CL-In was
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transparently lower than that of L-In at each temperature point, the trend was also
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applicable to S-In and CS-In, implying that crossed-linked inulin displayed stronger
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thermal stability than corresponding native inulin. The superior thermal stability of
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CL-In was attributed to the higher DP and greater molecular weight than S-In and
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L-In. This phenomenon may be simply explained as with the higher DP, thermal
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stability becomes stronger for intermolecular interaction of cross-linked inulin and
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harder for chemical bond to break when heated. The result obtained corresponded
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with that of Kim et al. (2001) who noticed an increase in reducing sugar content due
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to heating for the samples at neutral pH, from which they supposed that hydrolysis
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happened and inulin molecules were broken down into shorter chains. Besides, Bohm
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et al. (2005) also reported significant degradation of inulin was observed for
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found after 30 min of heating, increasing to nearly complete degradation after 60 min.
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However, these results did not corroborate with the study of Glibowski and Bukowska
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(2008), who showed that inulin was chemically stable even at 80 °C in the neutral
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environment. The different DP of inulin adopted may be the major contributor to the
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different results presented in different articles. In our work, only less than 2 % RRS
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(%) occurred for all four inulin under 100 °C, demonstrating only a very small
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amount of inulin were broken down into reducing sugar. An interesting find could be
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observed in Fig.3 (a) that S-In with the lowest DP (average DP = 4.30) exhibited
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highest RRS (%) whereas CL-In with highest DP (average DP = 15.10) exhibited
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lowest RRS (%), which showed that inulin with higher DP owned stronger ability to
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resist heating degradation. The average DP of inulin adopted by Glibowski and
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Bukowska (2008) was more than 23, so the inulin with an average DP of 23 was more
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difficult to break down to reducing sugar under the 80 °C.
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Acid stability of S-In, L-In, CS-In and CL-In was investigated in pH value ranging
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from 1 to 7. As shown in Fig. 3(b), the effect of pH value on inulin degradation was
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transparent when acidity rising. RRS (%) of inulin sharply rose with the decrease of
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pH value during pH value was under 6. This phenomenon indicated that inulin
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breakdown and hydrolysis occurred in an acidic environment (pH < 6). Similar with
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thermal stability test, RRS (%) of CL-In was lower than that of S-In, L-In and CS-In
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at every pH point, this indicated that the acid stability of inulin was markedly
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transform into reducing sugar under acidic conditions (Dan, Ghosh, & Moulik, 2010).
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3.5 Moisture absorption capability
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Moisture absorption capabilities of S-In, L-In, CS-In and CL-In were
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investigated at 81% RH (Fig. 4(a)). Fig. 4(a) showed that moisture absorption content
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of all four inulin steadily increased along with the time at room temperature. Basically,
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moisture absorption of all four inulin was quick in the first 24 h conditioning,
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afterwards all curves turned into level (Liu, Dong, Men, Jiang, Tong, & Zhou, 2012).
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Moisture absorption kinetics was also examined at 92% RH. The moisture absorption
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trend at 92% RH (Fig. 4(b)) was same as at 81% RH. However, for each kind of
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inulin, the equilibrium moisture content at 92% RH was clearly higher than that at 81%
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RH, which attributed to higher relative humidity at different conditions. The S-In
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exhibited marked higher moisture absorption ability than L-In at all the time, which
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also occurred between CS-In and CL-In. This phenomenon implied that inulin with
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lower DP owned stronger water-binding ability due to lots of external hydroxyl
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groups, which could explain the result obtained by Luo et al. (2017) that inulin with
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lower DP had the stronger influence on the pasting temperature and displayed
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stronger suppression on the retrogradation of wheat starch. Another interesting find
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was that after cross-linking, the cross-linked inulin (CS-In and CL-In) showed a
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notable higher moisture uptake than the corresponding native inulin (S-In and L-In) at
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to the enhancement of moisture uptake ability of cross-linked inulin.
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3.6 Rheological properties of inulin suspensions
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In order to understand the rheological properties, the steady shear viscoelastic
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properties of the dispersions of S-In, L-In, CS-In and CL-In were investigated. Fig. 5
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((a), (b), (c) and (d)) exhibited the dependent relationship between viscosity and shear
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rate at different inulin concentration. All of the flow curves of measured inulin
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dispersions presented shear-thinning behavior under the entire measured shear rates
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(1~500 s-1), because the viscosity remarkably declined as the shear rate increased.
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This phenomenon could be explained by the fact that shear action contributed to
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directional motion of inulin molecules in dispersions, so that the molecular orientation
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and flow direction tended to be the same, and the intermolecular interaction force was
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weakened, resulting in the decline of viscosity (Olivi-Tran, Botet, & Cabane, 1998).
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The shear-thinning behavior of cross-linked inulin could be applied in food
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processing. Due to the lower viscosity at high shear rate, the cross-linked inulin could
325
be used in mixing and pumping operations to reduce energy consumption. Besides,
326
the viscosities of all the four dispersions were dependent on the inulin concentration,
327
the larger the inulin concentration, the higher were the viscosities. Higher density of
328
chain entanglements could possibly be the major contributor to higher viscosities.
329
Moreover, we could observe that the viscosities of L-In and CL-In dispersions (Fig. 5
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CS-In (Fig. 5 ((a), (b)), and this trend still remained at low concentration (5%~20%)
332
but not very obviously. These demonstrated that inulin dispersion with greater DP
333
owned higher viscosities. This demonstration may provide another explanation for the
334
result revealed by Guimaraes et al. (2018b) that inulin with higher DP was more
335
effective for stabilization of prebiotic whey beverage, which authors attributed to the
336
stronger ability of higher DP inulin to form a three-dimensional network to stabilize
337
the two phases.
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The shear-thinning rheological behavior could be characterized by a power law constitutive equation. The power law equation may be written as
340
(4)
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where τ is the shear viscosity (Pa), K is the front consistency index, Υ is the shear rate,
342
and n is the power law exponent. When n is less than 1, it means the material is a
343
pseudoplastic fluid, when the exponent (n) is equal to 1, the material is a Newtonian
344
fluid and when n is higher than 1, the material is a dilatant fluid (Hong, Wu, Liu, &
345
Gu, 2015). The power law constitutive equation (4) was used to fit shear-thinning
346
viscosity values for all measured inulin dispersions. The results of these fit data are
347
summarized in Table 2. Overall, the values of n were all less than one for inulin
348
shear-thinning behavior, and the values of K increased with the increase of inulin
349
concentration and DP. The apparent viscosity (η100) at a given shear stress of 100 s-1
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351
increasing DP and concentration of inulin gave rise to the increase of the viscosity for
352
each type of inulin dispersions. The apparent viscosity at a given concentration of 40 %
353
was presented in Fig. 6(a). We observed that the inulin DP led to an increase of the
354
viscosity of the inulin dispersions as: S-In < CS-In < L-In < CL-In. The significant
355
increase of this viscosity was probably due to the enhanced interactions of inulin
356
molecular and flow resistance.
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The rheogram depicted in Fig. 6(b) showed the effect of temperature on the inulin
358
rheological properties at a steady shear rate of 50 s-1. We observed that the viscosity
359
of S-In and L-In decreased gradually with the increase of temperature. Viscosity of
360
CS-In as well as CL-In increased first and then decreased with the rise in temperature.
361
The reason for these may be that the increasing temperature enhanced intermolecular
362
motion, which led to increasing viscosity. However, as temperature increased further,
363
inulin solubility increased resulting in declining flow resistance and the decrease of
364
viscosity (Paula & Rodrigues, 1995).
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Fig. 6(c) showed the measurement results of dynamic frequency sweep for 40 %
366
dispersions of inulin (S-In, L-In, CS-In and CL-In). Viscoelastic properties of four
367
kinds of dispersions exhibited similar trend. Both G’ and G’’ moduli curves were
368
slightly dependent on frequency (w). The G’ for all S-In, L-In, CS-In and CL-In
369
dispersions were obviously greater than G’’ over the measured frequency sweep,
19
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371
and G’’ moduli for the CS-In and CL-In dispersions were correspondingly greater
372
than those of S-In and L-In dispersions, due to the higher DP with cross-linked inulin.
373
The G’ at entire measured frequency points increased as: S-In < CS-In < L-In < CL-In
374
(Fig. 6(c)). The result suggested that the CL-In dispersion exhibited most solid-like
375
viscoelastic behavior among the four types of dispersions, and CL-In dispersion
376
should be a strong gel-like material. These may be caused by the stronger
377
intermolecular interaction and greater molecular chain entanglements among
378
cross-linked inulin molecular (Tong, Liu, Veeramani, & Chung, 2002). The gel-like
379
behavior of the CL-In dispersion suggests many potential applications not only in
380
food processing, but also in cosmetic products and drug delivery. According to
381
Edwards’ theory (Doi & Edwards, 1986), the high-frequency moduli behavior of the
382
samples could display some information of the structure. The frequency moduli
383
behavior was determined by log–log complex moduli |G*| (|G| = (G’2 + G’’2)1/2) curve
384
slope at frequencies ranging from 1 to 100 rad/s. The frequency moduli for the L-In
385
and CL-In dispersions were all proportional to w1/2 well (Fig. 6(d)), indicating flexible
386
coil-like behavior of inulin (Ferry, 1980). Over the measured frequency range, the
387
S-In and CS-In dispersions did not show moduli proportional to w1/2 due to the
388
scattered experimental data points, which implied the S-In and CS-In couldn’t exhibit
389
the behavior of flexible chains.
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4. Conclusions
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392
different DP (CS-In and CL-In) was successfully prepared using SH as cross-linker in
393
this work. When compared with corresponding native S-In and L-In, we found that
394
CS-In and CL-In exhibited a higher intrinsic viscosity, moisture absorption capability,
395
thermal and acid stability, but with lower water solubility because of the higher DP.
396
Furthermore, in the study of rheological properties, all four inulin dispersions
397
exhibited shear-thinning behaviors, which could be described as a pseudoplastic fluid.
398
In addition, CL-In showed more solid viscoelastic properties due to the higher DP
399
when compared with the other three inulin dispersions. In summary, viscoelastic
400
behaviors of cross-linked dispersions were dependent on the DP and concentration of
401
inulin. Therefore, it is evident that cross-linked inulin can have potential applications
402
as a food addictive to regulate the rheology and texture of the products through using
403
inulin with different DP or different concentrations. Moreover, cross-linked inulin
404
prepared through this novel method could have significant application potential for
405
cosmetic gels and drug delivery carriers. Currently, further research has been done on
406
specific application of CL-In used as a stabilizer in set yoghurt processing.
407
Acknowledgments
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This work was financially supported by the special project for people's livelihood
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of Chongqing municipal science and technology commission [cstc2015shmszx0367];
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and national natural science foundation of China [31471581].
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References
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Barclay, T., Ginicmarkovic, M., Cooper, P., & Petrovsky, N. (2010). Inulin - a versatile polysaccharide with multiple pharmaceutical and food chemical uses.
414
Journal of Excipients & Food Chemicals, 1(3), 27 - 50.
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413
Balthazar C. F., Santillo, A., Figliola, L., Silva, H.L.A., Esmerino, E.A., Freitas, M. Q.,
416
et al. (2018a). Sensory evaluation of a novel prebiotic sheep milk strawberry
417
beverage. LWT - Food Science and Technology, 98, 94–98.
418
https://doi.org/10.1016/j.lwt.2018.08.017.
M AN U
SC
415
Balthazar, C.F., Silva, H.L.A., Cavalcanti, R.N., Esmerino, E.A., Cappato, L.P., Abud,
420
Y. K. D., et al. (2017). Prebiotics addition in sheep milk ice cream: A rheological,
421
microstructural and sensory study. Journal of Functional Foods, 35, 564–573.
422
http://dx.doi.org/10.1016/j.jff.2017.06.004.
Balthazar, C. F., Silva, H. L. A., Esmerino, E. A., Rocha, R. S., Moraes, J., Carmo, M.
EP
423
TE D
419
A.V., et al. (2018b). The addition of inulin and Lactobacillus casei 01 in sheep
425
milk ice cream. Food Chemistry, 246, 464–472.
426 427
AC C
424
https://doi.org/10.1016/j.foodchem.2017.12.002.
Bohm, A., Kaiser, I., Trebstein, A., & Henle, T. (2005). Heat-induced degradation of
428
inulin. European Food Research & Technology, 220, (5-6), 466-471.
429
https://doi.org/10.1007/s00217-004-1098-8. 22
ACCEPTED MANUSCRIPT 430
Canbulat, Z., & Ozcan, T. (2015). Effects of Short‐Chain and Long‐Chain Inulin on the Quality of Probiotic Yogurt Containing Lactobacillus rhamnosus. Journal
432
of Food Processing & Preservation, 39 (6), 1251–1260.
433
https://doi:10.1111/jfpp.12343.
436
University Press.
SC
435
Doi, M. & Edwards, S. F. (1986). The theory of polymer dynamics. London: Oxford
Dan A., Ghosh S., & Moulik S. P. (2010). Physicochemical studies on the biopolymer
M AN U
434
RI PT
431
437
inulin: a critical evaluation of its self-aggregation, aggregate-morphology,
438
interaction with water, and thermal stability. Biopolymers, 91 (9), 687-699.
439
http://dx.doi.org/10.1002/bip.21199.
Freitas, R. A., Gorin, P. A.J., Neves, J., & Sierakowski, M. R. (2003). A rheological
TE D
440
description of mixtures of a galactoxyloglucan with high amylose and waxy corn
442
starches. Carbohydrate Polymers, 51(1), 25 - 32.
443
http://dx.doi.org/10.1016/S0144-8617(02)00095-4.
445 446
Ferry, J. D. (1980). Viscoelastic properties of polymers (3rd ed.). New York: John
AC C
444
EP
441
Wiley & Sons.
García, P., Vega, J., Jimenez, P., Santos, J. & Robert, P. (2013). Alpha-tocopherol
447
microspheres with cross-linked and acetylated inulin and their release profile in a
448
hydrophilic model. European Journal of Lipid Science & Technology, 115(7), 23
ACCEPTED MANUSCRIPT 449 450
811-819. https://doi.org/10.1002/ejlt.201200109.
García, P., Vergara, C. & Robert, P., (2015). Release Kinetic in Yogurt from Gallic Acid Microparticles with Chemically Modified Inulin. Journal of Food Science,
452
80(10), 2147-2152. http://dx.doi.org/10.1111/1750-3841.13001.
RI PT
451
Glibowski, P., & Bukowska, A. (2011). The effect of pH, temperature and heating
454
time on inulin chemical stability. Acta Scientiarum Polonorum: Technologia
455
Alimentaria, 10 (2), 188-214.
M AN U
456
SC
453
Gibson, G. R., Hutkins, R., Sanders, M. E., Prescott, S. L., Reimer, R. A., Salminen, S. J., et al. (2017). The International Scientific Association for Probiotics and
458
Prebiotics ISAPP consensus statement on the definition and scope of prebiotics.
459
Nature Reviews Gastroenterology & Hepatology, 14, 491–502.
460
TE D
457
Guimarães, J. T., Silva, E. K., Alvarenga, V. O., Costa, A., Cunha, R. L., Freitas, M. Q., et al. (2018a). Physicochemical changes and microbial inactivation after
462
high-intensity ultrasound processing of prebiotic whey beverage applying
463
different ultrasonic power levels. Ultrasonics – Sonochemistry, 44, 251–260.
AC C
464
EP
461
https://doi.org/10.1016/j.ultsonch.2018.02.012.
465
Guimarães, J. T., Silva, E. K., Costa, A. L. R., Cunha, R. L., Freitas, M. Q., Meireles,
466
M. A. A., et al. (2018b). Manufacturing a prebiotic whey beverage exploring the
467
influence of degree of inulin polymerization. Food Hydrocolloids, 77, 787-795.
24
ACCEPTED MANUSCRIPT 468 469
https://doi.org/10.1016/j.foodhyd.2017.11.021.
Hong Y., Wu Y., Liu G. & Gu Z. (2015) Effect of amylose on pasting and rheological properties of corn starch/xanthan blends. Starch/Stärke, 67, 98–106.
471
http://dx.doi.org/10.1002/star.201400126.
472
RI PT
470
Kim, Y., Faqih, M.N., & Wang, S.S. (2001). Factors affecting gel formation of inulin. Carbohydrate Polymers, 46 (2), 135-145.
474
https://doi.org/10.1016/S0144-8617(00)00296-4.
M AN U
475
SC
473
Luo, D., Li, Y., Xu, B, Ren, G., Li, P., Li, X., et al. (2017). Effects of inulin with different degree of polymerization on gelatinization and retrogradation of wheat
477
starch. Food Chemistry, 229, 35–43.
478
http://dx.doi.org/10.1016/j.foodchem.2017.02.058.
479
TE D
476
Liu, Z., Dong, Y., Men, H., Jiang, M., Tong, J. & Zhou, J. (2012). Post-crosslinking modification of thermoplastic starch/PVA blend films by using sodium
481
hexametaphosphate. Carbohydrate Polymers, 89 (2), 473-477.
482
http://dx.doi.org/10.1016/j.carbpol.2012.02.076.
484
AC C
483
EP
480
Li, S.P., Hu, T., Chen, Y.L., Zheng, C.Y., Liu, T., Ma, G.H., et al. (2010). Cross-linked inulin as a potential plasma expander: Biochemical properties and physiological
485
characterization in a rabbit model. Carbohydrate Polymers, 82(4), 1054-1060.
486
https://doi.org/10.1016/j.carbpol.2010.06.018.
25
ACCEPTED MANUSCRIPT 487 488 489
Miller, G.L. (1959). Use of DinitrosaIicyIic acid reagent for determination of reducing sugar. Analytical Chemistry, 31(3), 426-428.
Naskar, B., Dan A., Ghosh S., & Moulik S. P. (2010). Characteristic physicochemical features of the biopolymer inulin in solvent added and depleted states.
491
Carbohydrate Polymers, 81, 700–706.
492
http://dx.doi.org/10.1016/j.carbpol.2010.03.041.
SC
493
RI PT
490
Naskar B., Dan A., Ghosh S., & Moulik S. P. (2010). Viscosity and Solubility Behavior of the Polysaccharide Inulin in Water, Water plus Dimethyl Sulfoxide,
495
and Water plus Isopropanol Media. Journal of Chemical & Engineering Data,
496
55(7), 2424-2427. http://dx.doi.org/10.1021/je900834c.
Olivi-Tran, N., Botet, R., & Cabane, B. (1998). Monte Carlo simulations of colloidal
TE D
497
M AN U
494
dispersions under shear. Physical Review E, 57 (57), 1997-2003.
499
http://dx.doi.org/10.1103/PhysRevE.57.1997.
501 502 503
Pawel, G., & Adam, W. (2008). Effect of thermochemical treatment on the structure of inulin and its gelling properties. International Journal of Food Science &
AC C
500
EP
498
Technology, 43(11), 2075-2082. http://dx.doi.org/10.1111/j.13652621.2008.01825.x.
504
Paula, R.C.M. & Rodrigues, J.F. (1995). Composition and rheological properties of
505
cashew tree gum, the exudate polysaccharide from Anacardium occidentale L.
26
ACCEPTED MANUSCRIPT 506
Carbohydrate Polymers, 26 (95), 177–181.
507
https://doi.org/10.1016/0144-8617(95)00006-S.
508
Palma, M., García, P., & Márquez, R. G., (2014). Vergara, C., Robert, P. Release kinetics of flavonoids in methyl linoleate from microparticles designed with
510
inulin and channelizing agent. Food Research International, 64, 99 – 105.
511
http://dx.doi.org/10.1016/j.foodres.2014.05.064.
SC
512
RI PT
509
Ren, L., Jiang, M., Wang, L., Zhou, J., & Tong, J. (2012). A method for improving dispersion of starch nanocrystals in water through crosslinking modification with
514
sodium hexametaphosphate. Carbohydrate Polymers, 87(2), 1874-1876.
515
https://doi.org/10.1016/j.carbpol.2011.08.070.
Shoaib M., Shehzad A., Omar M., Rakha A., Raza H., Sharif H.R., et al. (2016).
TE D
516
M AN U
513
Inulin: Properties, health benefits and food applications. Carbohydrate Polymers,
518
147, 444-454. http://dx.doi.org/10.1016/j.carbpol.2016.04.020.
520 521 522 523 524
Tong, Y., Liu, T. Veeramani, S., & Chung, T. (2002). Bulk Viscosity and Its Unstable Behavior upon Storage in Polyimide Precursor Solutions. Industrial &
AC C
519
EP
517
Engineering Chemistry Research, 41(17), 4266 - 4272. http://dx.doi.org/10.1021/ie020159f.
Vervoort L., Mooter G. V. d., Augustijns P., Busson R., Toppet S., & Kinget R. (1997) Inulin hydrogels as carriers for colonic drug targeting: I. Synthesis and
27
ACCEPTED MANUSCRIPT 525
characterization of methacrylated inulin and hydrogel formation. Pharmaceutical
526
Research, 14 (12), 1730-1737. http://dx.doi.org/10.1023/A:1012179813102.
Wang Z., Gu Z., Li Z., Hong Y., & Cheng L. (2013). Effects of urea on freeze–thaw
528
stability of starch-based wood adhesive. Carbohydrate Polymers, 95, 397- 403.
529
https://doi.org/10.1016/j.carbpol.2013.02.009.
Wang N., Fu Q., & Yang G. (2012). Determination of the solubility, dissolution
SC
530
RI PT
527
enthalpy and entropy of icariin in water, ethanol, and methanol. Fluid Phase
532
Equilibria, 324, 41– 43. http://dx.doi.org/10.1016/j.fluid.2012.03.022.
533
M AN U
531
Zhang, T., Tian, Y., Jiang, B., & Ming, M. (2014). Purification, preliminary structural characterization and in vitro antioxidant activity of polysaccharides from
535
Acanthus ilicifolius. LWT - Food Science and Technology, 56(1), 9-14.
536
https://doi.org/10.1016/j.lwt.2013.11.010.
Zhou J., Zhang J., Ma Y., & Tong J. (2008). Surface photo-crosslinking of corn starch
EP
537
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534
sheets. Carbohydrate Polymers, 74, 405 - 410.
539
http://dx.doi.org/10.1016/j.carbpol.2008.03.006.
540 541
AC C
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Zhang, F., Fang, L., Wang, C., Shi, L., Chang, T., Yang, H., & Cui, M. (2013). Effects of starches on the textural, rheological, and color properties of surimi–beef gels
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with microbial tranglutaminase. Meat Science, 93, 533–537.
543
http://dx.doi.org/10.1016/j.meatsci.2012.11.013.
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Table 1 Average Mw, average DP, intrinsic viscosity, and water solubility of S-In, L-In, CS-In and CL-In.
Average
Average DP
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Intrinsic
Solubility (g/100g)
Mw (Da)
40℃
60℃
80℃
26.86±0.82aD
40.82±0.31aC
46.79±0.21aB
49.62±0.88aA
8.30±0.48bD
14.61±0.13bC
21.36±0.06bB
32.35±0.07bA
877±21d
4.30±0.16d
1.53±0.11d
CS-In
1295±32c
6.88±0.19c
2.43±0.14c
L-In
2022±53b
11.37±0.33b
4.85±0.20b
1.97±0.16cD
7.68±0.20cC
11.76±0.25cB
20.70±0.93cA
CLNI
2626±58a
15.10±0.36a
1.21±0.02cC
4.08±0.10dB
7.39±0.16dA
7.68±0.01dA
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viscosity (dL/g)
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6.78±0.53a
545
Mean values followed by the different letter (a−d) in each column are significantly different (p ≤ 0.05). Mean values followed by the different
546
letter (A−D) for temperature in each row are significantly different (p ≤ 0.05). 29
ACCEPTED MANUSCRIPT Table 2 Power law model-fitted parameters.
5%
0.0073
10%
n
R2
0.1528
0.3393
0.9718
0.0069
0.1134
0.3918
0.9759
20%
0.0088
0.2823
30%
0.0096
0.3019
40%
0.0115
0.3231
50%
0.0114
0.3283
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(Pa•s )
5%
0.0079
0.198
0.3
0.9926
10%
0.0097
0.2095
0.3337
0.9663
0.2467
0.9723
0.2508
0.9636
0.2756
0.9336
0.2702
0.9442
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n
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L-In
0.0339
0.7737
0.3209
0.9604
0.5376
29.0582
0.1336
0.9692
1.083
62.1779
0.1205
0.9754
3.093
170.4428
0.1294
0.9926
0.0077
0.1959
0.2972
0.9828
10%
0.0208
0.4444
0.3353
0.971
20%
0.0207
0.4533
0.3297
0.9753
30%
0.0223
0.5776
0.2935
0.9697
40%
0.0205
0.516
0.2997
0.9726
50%
0.0286
0.7474
0.2912
0.9624
5%
0.0115
0.6878
0.112
0.9655
10%
0.0123
0.5904
0.1593
0.9312
20%
0.0351
1.16
0.2405
0.9314
30%
0.5953
37.2853
0.1016
0.976
40%
1.6531
117.1904
0.0747
0.9583
50%
4.0509
218.8529
0.1337
0.9762
30% 40% 50%
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5%
CL-In
K
(Pa•s)
S-In
CS-In
η100
Concentration (%)
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Fig. Captions
549
Fig.1 IR spectra of CL-In (a), L-In (b), CS-In (c) and S-In (d).
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Fig.2 SEM images of S-In powder (a), L-In powder (b), CS-In powder (c) and CL-In
552
powder (d).
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Fig.3 Thermal stability of four kinds of inulin (a), acid stability of four kinds of inulin
555
(b). (Coordinate values followed by the different letter (A−C) for different inulin at
556
same condition are significantly different (p ≤ 0.05). Coordinate values followed by
557
the different letter (a−f) for each inulin at different conditions are significantly
558
different (p ≤ 0.05)).
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Fig.4 The moisture absorption content of four kinds of inulin at 81 % RH (a), and 92 %
561
RH (b). (Coordinate values followed by the different letter (A−D) for different inulin
562
at same time are significantly different (p ≤ 0.05). Coordinate values followed by the
563
different letter (a−c) for each inulin at different time are significantly different (p ≤
564
0.05)).
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Fig.5 The viscoelastic properties of the steady shear measurements for S-In (a), CS-In
567
(b), L-In (c) and CL-In (d) dispersions of 5%, 10%, 20%, 30%, 40%, and 50% (w/v)
568
at a temperature of 25 °C.
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Fig.6 The viscoelastic properties of the steady shear measurements for S-In, L-In,
571
CS-In and CL-In dispersions of 40% (w/v) at a temperature of 25 °C (a); Temperature
572
dependence of viscosity for S-In, L-In, CS-In and CL-In dispersions of 40 % (w/v) at
573
a steady shear rate of 50 s-1 (b); The viscoelastic properties of dynamic frequency
574
sweep measurements for the 40% dispersions of inulin at a temperature of 25 °C (c);
575
The viscoelastic properties of dynamic frequency sweep measurements (values of
576
complex modulus (G*) vs. frequency) for the 40% dispersions of S-In, L-In, CS-In
577
and CL-In at a temperature of 25 °C (d).
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ACCEPTED MANUSCRIPT Research highlights (1) Cross-linked inulin was prepared using sodium hexametaphosphate as cross-linker.
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(2) Polymerization degree has marked effects on physicochemical properties of cross-linked inulin.
(3) Cross-linked inulin exhibited as a pseudoplastic fluid and more solid viscoelastic
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properties.
S0268-005X(18)31606-0
DOI:
https://doi.org/10.1016/j.foodhyd.2018.11.026
Reference:
FOOHYD 4767
To appear in:
Food Hydrocolloids
Received Date: 22 August 2018 Revised Date:
15 October 2018
Accepted Date: 12 November 2018
Please cite this article as: Li, Y., Ma, X., Liu, X., Physicochemical and rheological properties of cross-linked inulin with different degree of polymerization, Food Hydrocolloids (2018), doi: https:// doi.org/10.1016/j.foodhyd.2018.11.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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ACCEPTED MANUSCRIPT Physicochemical and rheological properties of cross-linked inulin
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with different degree of polymerization
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Yao Li, Xiaohan Ma, Xiong Liu*
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College of Food Science, Southwest University, Chongqing, 400715, China
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* Corresponding author: Xiong Liu
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Address: No. 2 Tiansheng Road, Beibei District, Chongqing, 400715, P. R. China
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Tel: +86-23-68250375
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Fax: +86-23-68251947
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E-mail: [email protected] (X. Liu)
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ACCEPTED MANUSCRIPT Abstract: Long-chain inulin (L-In) and short-chain inulin (S-In) from native inulin
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was separated through the method of alcohol precipitation. Cross-linked inulin with
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two different degree of polymerization (average DP = 6.88 and 15.10) were prepared
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in aqueous solutions by using the L-In and S-In respectively as raw material and
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sodium hexametaphosphate as cross-linker. Structural characteristics of cross-linked
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inulin were determined by Fourier-transform infrared spectroscopy and scanning
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electron microscopy. Compared with native L-In and S-In, cross-linked inulin had a
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higher intrinsic viscosity, stronger stability and moisture absorption capability, but
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lower water solubility. Only 1% reducing sugar produced when cross-linked inulin
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was heated within 100 °C, and inulin hydrolysis occurred in acidic environment (pH <
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6). Rheological properties of inulin dispersions with different degree of
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polymerization were investigated and compared. The viscoelastic properties of steady
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shear measurements indicated that cross-linked inulin dispersions presented
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shear-thinning behaviors, which could be described by a power law model with
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determination coefficients (R2 = 0.9312~0.9926). The viscoelastic properties of
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dynamic frequency sweep measurements indicated that cross-linked inulin dispersion
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showed more solid viscoelastic properties than corresponding native inulin
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dispersions.
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Keywords: cross-linked; inulin; polymerization degree; physicochemical property;
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rheological property.
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1. Introduction Prebiotics are substrates selectively utilized by host microorganisms conferring a
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health benefit (Gibson et al., 2017). Inulin, known as a rising attractive prebiotic, is
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composed of D-furan fructose units and one terminal glucose unit, exhibiting many
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beneficial physiological functions, such as antioxidant activity, ability to improve
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colonic microbiota, promote mineral absorption, regulate blood glucose and blood
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lipids (Balthazar et al., 2018a; Shoaib et al., 2016). Ranging from 2 to 60
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monosaccharide units, the degree of polymerization (DP) of natural inulin have an
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effect on the physicochemical properties of inulin (Barclay, Ginicmarkovic, Cooper,
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& Petrovsky, 2010). Generally, short-chain inulin can contribute to an improved
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mouth feel due to good solubility and mild sweetness, and long-chain inulin can act as
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fat replacer or texture modifier due to its poor solubility and good viscosity stability.
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Based on nutritional and physicochemical properties, inulin has been widely used in
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an increasing number of applications throughout the food production. The prebiotic
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inulin have proven to be a promising fat substitute and to improve the functional
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potential in sheep milk ice cream formulation (Balthazar et al., 2017; Balthazar et al.,
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2018b); the use of inulin could be used for prebiotic in the formulation of whey
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beverage (Guimaraes et al., 2018a). Besides, the use of inulin for prebiotic in
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probiotic yogurt could enhance the viability of lactobacillus during storage (Canbulat
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& Ozcan, 2015).
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ACCEPTED MANUSCRIPT However, native inulin may induce a disadvantageous rapid renal excretion due to
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its low molecular weights (Mw). Cross-linking of inulin to enhance its Mw is a
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strategy to avoid this disadvantage (Li, Hu, Chen, Zheng, Liu, & Ma, et al. 2010).
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Currently, there have been some reports on the synthesis methods of cross-linked
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inulin. For example, García synthesized cross-linked inulin using phosphoryl chloride
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as the cross-linker under alkaline condition (García, Vergara, & Robert, 2015); the
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cross-linked inulin was prepared by Li’s method using epichlorohydrin as the
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cross-linker to conjoin inulin molecules (Li et al., 2010); on the other hand, Vervoort
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synthesized cross-linked inulin with glycidyl methacrylate to introduce double bonds
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in a radical polymerization (Vervoort et al., 1997). These present methods for
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preparation of cross-linked inulin feature various disadvantages, such as long
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preparation time, high toxicity of cross-linker and violent reaction conditions.
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Therefore, a novel method for cross-linked inulin with advantages, such as gentle
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reaction condition, time saving, absence of side-effect and simple operation is
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desirable. Moreover, in those reported works, native inulin (a mixture of long-chain
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and short-chain inulin) was cross-linked immediately without classification before
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crosslinking, resulting in the variable DP of cross-linked inulin leading to weak
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compatibility and instability. Therefore, systematic research on physicochemical and
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rheological properties of cross-linked inulin with different DP is lacking which limit
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the deeper-level analysis and application of inulin in the food production.
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This study aimed to develop a commercially novel method for preparation of 4
ACCEPTED MANUSCRIPT cross-linked inulin for potential industrial application and to evaluate the
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physicochemical and rheological properties of cross-linked inulin with different DP.
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2. Materials and methods
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2.1. Materials
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Native inulin (average DP < 10) was supplied by Xi’an Ruiling Technology Co.,
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Ltd. (Xi’an, China). Anhydrous ethanol, sodium hexametaphosphate (SH), anhydrous
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sodium carbonate, hydrochloric acid, sulfuric acid, nitric acid, hydroquinone, standard
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polyethylene glycols, 3,5-dinitrosalicylic acid and phenol were purchased from
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Kelong Chemical Reagent Factory (Chengdu, China). All reagents were of analytical
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grade.
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2.2 Preparation of cross-linked inulin
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16 g of native inulin was added to 80 mL distilled water at room temperature and
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gently stirred until dissolved. Then 20 mL of anhydrous ethanol was added into the
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solution. The mixture solution was stored at 4 °C for 24 hours. Then sediment and
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liquid supernatant were separated by centrifugation. After lyophilizing for sediment,
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long-chain inulin (L-In) in native inulin was obtained. After condensation and
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lyophilizing for liquid supernatant, short chain inulin (S-In) were obtained.
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Cross-linked inulin was prepared via a method similar to that of starch modification
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(Ren, Jiang, Wang, Zhou, & Tong, 2012; Liu, Dong, Men, Jiang, Tong, & Zhou, 2012). 5
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at 25 °C and then 1.1 g of cross-linker SH was added followed by the addition of
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Na2CO3 (2 mol/L) until reached pH 10. Then the pre-polymerization solution was
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polymerized with continuous stirring at 45 °C for 3.5 h. Upon completion of the
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reaction, the pH of the suspension was adjusted to 7 with 2 mol/L HCl. Then
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cross-linked inulin was precipitated with 95% ethanol, followed by centrifugation and
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washing with anhydrous ethanol. Finally, after washings with water and lyophilizing,
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cross-linked long-chain inulin (CL-In) was obtained. Cross-linked short-chain inulin
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(CS-In) was prepared in the same manner but with the S-In in place of L-In.
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2.3 Structure characterization
Different inulin (L-In, S-In, CS-In and CL-In) were characterized by FT-IR
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(Equinox 55, China), the scanning range was from 400 cm−1 to 4000 cm−1. SEM
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analysis was performed by a scanning electron microscope (Sigma 300, Carl Zeiss
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Jena) with amplification at 10
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were sputter-coated with gold before analysis.
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2.4 Determination of inulin content
times (Palma, García, & Márquez, 2014); samples
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Inulin is a non-reducing polysaccharide, glucose and fructose contained in native
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inulin are reducing sugars. Total sugar content was determined by method of
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phenol-sulfuric acid, reducing sugar content was determined by the dinitrosalicylic
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acid (DNS) method (Miller, 1959). Ultraviolet and visible spectrophotometer 6
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to get the inulin content accurately, the reducing sugar content contained in native
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inulin was subtracted (Glibowski & Bukowska, 2011).
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W=
ρ-ρ1 ×V m
×100% (1)
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Where W is the inulin content in sample (%), ρ refers to the mass concentration of
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total sugar (mg/mL), ρ1 stands for the mass concentration of reducing sugars (mg/mL),
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V is the volume of the sample (mL), and m represents the amount of sample (mg).
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2.5 Determination for degree of polymerization
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Molecular weights (Mw) of different inulin (L-In, S-In, CS-In and CL-In) were
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determined by a high performance gel-filtration chromatography (HPGFC), which
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was performed on a high-performance liquid chromatography system (Agilent 1260,
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Germany) with a TSK-GEL GMPWXL column (7.8 × 300 mm) eluted with pure
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water at a flow fate of 0.7 mL/min (Zhang, Tian, Jiang, & Ming, 2014). Standard
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polyethylene glycols (600 Da, 1000 Da, 2000 Da, 4000Da, 10000 Da) were also
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applied to the same system. The molecular weight distributions of the samples were
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determined by comparison with the retention time of standard polyethylene glycols
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under the same conditions. The DP of inulin can be obtained according to Mw = 162
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DP + 180.
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2.6 Determination of solubility, viscosity, and stability
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2.6.1 Water Solubility
The solubility experiments were visually conducted in an illuminated condition in a
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thermostatic water bath. Water solubility of different inulin (L-In, S-In, CS-In and
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CL-In) were evaluated with 100 mL water in a beaker, which was then immersed in a
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water bath at 25 °C, 40 °C, 60 °C and 80 °C, respectively (Wang, Fu, & Yang, 2012;
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Naskar, Dan, Ghosh, & Moulik, 2010). The temperature was controlled by
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temperature regulator and water circulator in the experiment. Inulin and water mixture
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was stirred at 150 rpm to make the solution homogeneous. At each temperature, 0.1 g
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of inulin was added to water solution at a slow speed rate of 0.1 g/min until
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undissolved particles appeared in the solution. After equilibrium, stirring was
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discontinued and the solution was settled in water bath at the appropriate temperature
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for 1 h. Finally, the upper portion was collected, filtered, poured into a volumetric
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flask, and diluted to an appropriate concentration for content analysis.
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2.6.2 Intrinsic viscosity measurement
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With pure water as blank sample, an Ubbelohde viscometer (Ф0.57 mm - 4 mL)
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was applied to measure intrinsic viscosity of different inulin samples (L-In, S-In,
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CS-In and CL-In) at 25 °C. The flow time of a solution in the viscometer was taken
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after thermal equilibrium allowing 15 min time for each solution prior to
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measurement (Naskar, Dan, Ghosh, & Moulik, 2010).
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2.6.3 Thermal and acid stability
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stability (Glibowski & Bukowska, 2008). Reducing sugar content was determined
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through the dinitrosalicylic acid (DNS) method (Miller, 1959). Thermal stability tests
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were implemented using 20 mL of 10 mg/g different sample solution (L-In, S-In,
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CS-In and CL-In) immersed in water bath at 20, 40, 60, 70, 80, 100 °C for 1 h.
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Acid stability tests were implemented by adjusting pH of sample solution to
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different standard (1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0) with hydrochloric acid at 25 °C.
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After hydrolysis for 1 h, pH of the sample solution was adjusted to 7.0. RRS (%) can
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directly reflect on the increment of reducing sugar share.
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(2)
Where, m1 is the reducing sugar content after 1h, m2 represents the reducing sugar
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RRS % =
content before 1h, M is the total sugar content.
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2.7 Moisture absorption and holding capability measurement
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Moisture absorption was measured through the method similar to Zhou’s (Zhou,
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Zhang, Ma, & Tong, 2008). Different samples (L-In, S-In, CS-In and CL-In) were
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stored at room temperature in Conway desiccators with controlled relative humidity
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maintained by saturated salt solutions ((NH4)2SO4, Na2CO3), and the corresponding
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humidity were 81%, and 92% RH at room temperature. Samples were fully dried at
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80 °C and weighted (Wd) before put into desiccators. A set of dried sample were put
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ACCEPTED MANUSCRIPT into desiccators with a given humidity. After stored in desiccators for predetermined
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time (6, 12, 24, 36, 48, and 60 h), samples were taken out and weighted (Ww). The
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moisture content (%) was determined by Equation (3) and moisture sorption kinetic
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curves were plotted.
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–
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2.8 Rheological properties
(3)
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Moisture content % =
A rheometer (Discovery HR-2, TA Instruments Ltd., America) was used to
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determine the rheological properties of inulin suspension.
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2.8.1 Steady shear measurements
Different inulin (L-In, S-In, CS-In and CL-In) aqueous hydrocolloid dispersions
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were prepared through suspending in water at 25 °C at a concentration of 5 %, 10 %,
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20 %, 30 %, 40 %, 50 % (w/v) respectively and stored at 25 °C and used within 2
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days after the preparation. Inulin suspensions were loaded on the base plate and
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excessive sample was wiped off with a spatula. A thin layer of low-density silicone oil
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was covered on the periphery of geometry to minimize evaporation loss before
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measurement (Wang, Gu, Li, Hong, & Cheng, 2013). TA rheometer was used to
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determine the relationship between viscosity and shear rate. The measuring geometry
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employed was a parallel plate (40 mm in diameter). The gap size and testing
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temperature were set at 500 µm and 25 °C. A range of shear rate (1~500 s-1) was
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was tested at temperature ranging from 20 to 80 °C with a shear rate of 50 s-1 to
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investigate the effect of temperature on the steady rheological properties of inulin.
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2.8.2 Dynamic frequency sweep measurements
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A concentration of 40 % (w/v) for inulin aqueous hydrocolloid dispersions were
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used to investigate the dynamic rheological properties. Small-amplitude oscillatory
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shear experiments were conducted over a frequency (w) range of 1~100 rad/s at 25 °C,
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yielding the shear storage (G’) and loss (G’’) moduli. Strain value was set at 2 %,
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which was within its linear viscoelastic range (Freitas, Gorin, Neves, & Sierakowski,
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2003).
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2.9 Statistical analyses
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All experiments were conducted in triplicate for each sample, and results were
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expressed as mean ± standard deviation. All data were statistically compared between
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groups using one-way analysis of variance. Significant differences among the mean
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values were determined by Duncan’s multiple range test with p < 0.05.
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3. Results and discussion
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3.1 Structural characterization of different inulin
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FT-IR was employed to demonstrate successful cross-linking of inulin to ensure the
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increasing DP. Infrared spectra of CL-In (Fig. 1 (a)), L-In (Fig. 1 (b)), CS-In (Fig. 1 11
ACCEPTED MANUSCRIPT (c)) and S-In (Fig. 1 (d)) were registered and compared. As shown in Fig. 1, the
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spectra of L-In and S-In showed almost the same results just as CL-In and CS-In. The
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peak at 933 cm-1、1031 cm-1、3400 cm-1 represent skeleton absorption peaks of inulin.
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L-In displayed a stretching vibrational absorption peak of glycosidic bond at 1132 cm
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−1
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indicated by arrows. Besides, the stretching vibrational peak at 3200 ~ 3600cm
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CL-In was significantly weaker than that of L-In, indicating that hydroxyl was
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involved in nucleophilic substitution reaction. These results confirmed the successful
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crosslinking of inulin in this experiment.
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−1
as
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of
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, and CL-In displayed relatively strong band of organic phosphate at 1280 cm
SEM was employed to characterize the morphologies of L-In, S-In, CS-In and
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CL-In. Fig. 2 showed that the morphology of S-In (Fig. 2(a)), L-In (Fig. 2(b)), CS-In
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(Fig. 2(c)) and CL-In (Fig. 2(d)) in SEM micrographs significantly differed after they
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were amplified by 10 3 times. SEM images showed that S-In (Fig. 2(a)) and L-In (Fig.
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2(b)) (Fig. 2(b)) were found to comprise relatively smooth microspheres. In contrast,
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CS-In (Fig. 2(c)) and CL-In (Fig. 2(d)) displayed significantly rougher and more
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uneven clusters of polymer rather beads. The size of L-In microspheres was obviously
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larger than that of S-In. Polymers of CS-In and CL-In were irregular in shape, with
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noticeable indentation and roughness on surface of polymers these shows the effect of
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inlet temperature and solvent on the morphology characteristics (García, Vega,
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Jimenez, Santos, & Robert, 2013). In addition, high viscosity of CL-In may cause the
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occurrence of adhesion between the polymers.
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3.2 Purity and molecular weight (Mw) of inulin Purity of S-In, L-In, CS-In and CL-In was evaluated by the method of 2.4, and as
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86.13±4.09 %, 90.91±2.77 %, 91.64±1.57 %, and 93.54±2.31 %, respectively. The
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purity of S-In was relatively lower than the others, due to the involvement of diffluent
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small molecular like reducing sugar. Furthermore, the HPGFC results indicated that
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the average molecular weights of S-In, L-In, CS-In and CL-In were 877, 2022, 1295
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and 2626 Da (shown in Table 1), respectively. S-In (average DP = 4.30) and L-In
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(average DP = 11.37) could be separated by alcohol precipitation, because inulin with
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small molecular weight had a better solubility in alcohol and had not been precipitated.
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The average molecular weight of CL-In was 2626 Da, more than that of L-In (2022
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Da), indicating that cross-linked inulin with greater molecular weight and higher DP
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than native inulin was obtained, which lies in the fact that small inulin molecules were
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cross-linked by cross-linker, leading to the formation of a larger inulin molecule.
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3.3 Solubility and intrinsic viscosity
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Solubility data for inulin in water at different temperatures are presented in Table 1.
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As can be observed, solubility at a particular temperature increases as: CL-In < L-In <
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CS-In < S-In, indicating that the solubility of inulin decreased significantly with the
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increase of inulin DP. Besides, with the temperature increasing, the solubility of inulin
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increased whereas the solubility increment of inulin with higher DP was obviously
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smaller.
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L-In < CL-In, indicating inulin with better intrinsic viscosity could be obtained
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through cross-linking. This could be explained by the increase of DP and introduction
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of hydrophilic phosphoric acid groups. With higher intrinsic viscosity, CL-In could be
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a potential food additive to improve food texture.
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3.4 Thermal and acid stability of inulin
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Thermal stability of S-In, L-In, CS-In and CL-In was investigated in temperature
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ranging from 20 °C to 100 °C. As shown in Fig. 3(a), the rising temperature within
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100 °C had significant effects on RRS (%). Besides, RRS (%) of CL-In was
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transparently lower than that of L-In at each temperature point, the trend was also
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applicable to S-In and CS-In, implying that crossed-linked inulin displayed stronger
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thermal stability than corresponding native inulin. The superior thermal stability of
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CL-In was attributed to the higher DP and greater molecular weight than S-In and
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L-In. This phenomenon may be simply explained as with the higher DP, thermal
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stability becomes stronger for intermolecular interaction of cross-linked inulin and
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harder for chemical bond to break when heated. The result obtained corresponded
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with that of Kim et al. (2001) who noticed an increase in reducing sugar content due
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to heating for the samples at neutral pH, from which they supposed that hydrolysis
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happened and inulin molecules were broken down into shorter chains. Besides, Bohm
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et al. (2005) also reported significant degradation of inulin was observed for
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found after 30 min of heating, increasing to nearly complete degradation after 60 min.
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However, these results did not corroborate with the study of Glibowski and Bukowska
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(2008), who showed that inulin was chemically stable even at 80 °C in the neutral
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environment. The different DP of inulin adopted may be the major contributor to the
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different results presented in different articles. In our work, only less than 2 % RRS
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(%) occurred for all four inulin under 100 °C, demonstrating only a very small
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amount of inulin were broken down into reducing sugar. An interesting find could be
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observed in Fig.3 (a) that S-In with the lowest DP (average DP = 4.30) exhibited
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highest RRS (%) whereas CL-In with highest DP (average DP = 15.10) exhibited
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lowest RRS (%), which showed that inulin with higher DP owned stronger ability to
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resist heating degradation. The average DP of inulin adopted by Glibowski and
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Bukowska (2008) was more than 23, so the inulin with an average DP of 23 was more
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difficult to break down to reducing sugar under the 80 °C.
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Acid stability of S-In, L-In, CS-In and CL-In was investigated in pH value ranging
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from 1 to 7. As shown in Fig. 3(b), the effect of pH value on inulin degradation was
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transparent when acidity rising. RRS (%) of inulin sharply rose with the decrease of
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pH value during pH value was under 6. This phenomenon indicated that inulin
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breakdown and hydrolysis occurred in an acidic environment (pH < 6). Similar with
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thermal stability test, RRS (%) of CL-In was lower than that of S-In, L-In and CS-In
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at every pH point, this indicated that the acid stability of inulin was markedly
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transform into reducing sugar under acidic conditions (Dan, Ghosh, & Moulik, 2010).
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3.5 Moisture absorption capability
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Moisture absorption capabilities of S-In, L-In, CS-In and CL-In were
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investigated at 81% RH (Fig. 4(a)). Fig. 4(a) showed that moisture absorption content
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of all four inulin steadily increased along with the time at room temperature. Basically,
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moisture absorption of all four inulin was quick in the first 24 h conditioning,
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afterwards all curves turned into level (Liu, Dong, Men, Jiang, Tong, & Zhou, 2012).
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Moisture absorption kinetics was also examined at 92% RH. The moisture absorption
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trend at 92% RH (Fig. 4(b)) was same as at 81% RH. However, for each kind of
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inulin, the equilibrium moisture content at 92% RH was clearly higher than that at 81%
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RH, which attributed to higher relative humidity at different conditions. The S-In
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exhibited marked higher moisture absorption ability than L-In at all the time, which
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also occurred between CS-In and CL-In. This phenomenon implied that inulin with
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lower DP owned stronger water-binding ability due to lots of external hydroxyl
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groups, which could explain the result obtained by Luo et al. (2017) that inulin with
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lower DP had the stronger influence on the pasting temperature and displayed
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stronger suppression on the retrogradation of wheat starch. Another interesting find
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was that after cross-linking, the cross-linked inulin (CS-In and CL-In) showed a
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notable higher moisture uptake than the corresponding native inulin (S-In and L-In) at
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to the enhancement of moisture uptake ability of cross-linked inulin.
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3.6 Rheological properties of inulin suspensions
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In order to understand the rheological properties, the steady shear viscoelastic
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properties of the dispersions of S-In, L-In, CS-In and CL-In were investigated. Fig. 5
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((a), (b), (c) and (d)) exhibited the dependent relationship between viscosity and shear
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rate at different inulin concentration. All of the flow curves of measured inulin
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dispersions presented shear-thinning behavior under the entire measured shear rates
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(1~500 s-1), because the viscosity remarkably declined as the shear rate increased.
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This phenomenon could be explained by the fact that shear action contributed to
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directional motion of inulin molecules in dispersions, so that the molecular orientation
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and flow direction tended to be the same, and the intermolecular interaction force was
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weakened, resulting in the decline of viscosity (Olivi-Tran, Botet, & Cabane, 1998).
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The shear-thinning behavior of cross-linked inulin could be applied in food
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processing. Due to the lower viscosity at high shear rate, the cross-linked inulin could
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be used in mixing and pumping operations to reduce energy consumption. Besides,
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the viscosities of all the four dispersions were dependent on the inulin concentration,
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the larger the inulin concentration, the higher were the viscosities. Higher density of
328
chain entanglements could possibly be the major contributor to higher viscosities.
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Moreover, we could observe that the viscosities of L-In and CL-In dispersions (Fig. 5
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CS-In (Fig. 5 ((a), (b)), and this trend still remained at low concentration (5%~20%)
332
but not very obviously. These demonstrated that inulin dispersion with greater DP
333
owned higher viscosities. This demonstration may provide another explanation for the
334
result revealed by Guimaraes et al. (2018b) that inulin with higher DP was more
335
effective for stabilization of prebiotic whey beverage, which authors attributed to the
336
stronger ability of higher DP inulin to form a three-dimensional network to stabilize
337
the two phases.
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The shear-thinning rheological behavior could be characterized by a power law constitutive equation. The power law equation may be written as
340
(4)
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where τ is the shear viscosity (Pa), K is the front consistency index, Υ is the shear rate,
342
and n is the power law exponent. When n is less than 1, it means the material is a
343
pseudoplastic fluid, when the exponent (n) is equal to 1, the material is a Newtonian
344
fluid and when n is higher than 1, the material is a dilatant fluid (Hong, Wu, Liu, &
345
Gu, 2015). The power law constitutive equation (4) was used to fit shear-thinning
346
viscosity values for all measured inulin dispersions. The results of these fit data are
347
summarized in Table 2. Overall, the values of n were all less than one for inulin
348
shear-thinning behavior, and the values of K increased with the increase of inulin
349
concentration and DP. The apparent viscosity (η100) at a given shear stress of 100 s-1
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351
increasing DP and concentration of inulin gave rise to the increase of the viscosity for
352
each type of inulin dispersions. The apparent viscosity at a given concentration of 40 %
353
was presented in Fig. 6(a). We observed that the inulin DP led to an increase of the
354
viscosity of the inulin dispersions as: S-In < CS-In < L-In < CL-In. The significant
355
increase of this viscosity was probably due to the enhanced interactions of inulin
356
molecular and flow resistance.
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The rheogram depicted in Fig. 6(b) showed the effect of temperature on the inulin
358
rheological properties at a steady shear rate of 50 s-1. We observed that the viscosity
359
of S-In and L-In decreased gradually with the increase of temperature. Viscosity of
360
CS-In as well as CL-In increased first and then decreased with the rise in temperature.
361
The reason for these may be that the increasing temperature enhanced intermolecular
362
motion, which led to increasing viscosity. However, as temperature increased further,
363
inulin solubility increased resulting in declining flow resistance and the decrease of
364
viscosity (Paula & Rodrigues, 1995).
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Fig. 6(c) showed the measurement results of dynamic frequency sweep for 40 %
366
dispersions of inulin (S-In, L-In, CS-In and CL-In). Viscoelastic properties of four
367
kinds of dispersions exhibited similar trend. Both G’ and G’’ moduli curves were
368
slightly dependent on frequency (w). The G’ for all S-In, L-In, CS-In and CL-In
369
dispersions were obviously greater than G’’ over the measured frequency sweep,
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371
and G’’ moduli for the CS-In and CL-In dispersions were correspondingly greater
372
than those of S-In and L-In dispersions, due to the higher DP with cross-linked inulin.
373
The G’ at entire measured frequency points increased as: S-In < CS-In < L-In < CL-In
374
(Fig. 6(c)). The result suggested that the CL-In dispersion exhibited most solid-like
375
viscoelastic behavior among the four types of dispersions, and CL-In dispersion
376
should be a strong gel-like material. These may be caused by the stronger
377
intermolecular interaction and greater molecular chain entanglements among
378
cross-linked inulin molecular (Tong, Liu, Veeramani, & Chung, 2002). The gel-like
379
behavior of the CL-In dispersion suggests many potential applications not only in
380
food processing, but also in cosmetic products and drug delivery. According to
381
Edwards’ theory (Doi & Edwards, 1986), the high-frequency moduli behavior of the
382
samples could display some information of the structure. The frequency moduli
383
behavior was determined by log–log complex moduli |G*| (|G| = (G’2 + G’’2)1/2) curve
384
slope at frequencies ranging from 1 to 100 rad/s. The frequency moduli for the L-In
385
and CL-In dispersions were all proportional to w1/2 well (Fig. 6(d)), indicating flexible
386
coil-like behavior of inulin (Ferry, 1980). Over the measured frequency range, the
387
S-In and CS-In dispersions did not show moduli proportional to w1/2 due to the
388
scattered experimental data points, which implied the S-In and CS-In couldn’t exhibit
389
the behavior of flexible chains.
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4. Conclusions
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392
different DP (CS-In and CL-In) was successfully prepared using SH as cross-linker in
393
this work. When compared with corresponding native S-In and L-In, we found that
394
CS-In and CL-In exhibited a higher intrinsic viscosity, moisture absorption capability,
395
thermal and acid stability, but with lower water solubility because of the higher DP.
396
Furthermore, in the study of rheological properties, all four inulin dispersions
397
exhibited shear-thinning behaviors, which could be described as a pseudoplastic fluid.
398
In addition, CL-In showed more solid viscoelastic properties due to the higher DP
399
when compared with the other three inulin dispersions. In summary, viscoelastic
400
behaviors of cross-linked dispersions were dependent on the DP and concentration of
401
inulin. Therefore, it is evident that cross-linked inulin can have potential applications
402
as a food addictive to regulate the rheology and texture of the products through using
403
inulin with different DP or different concentrations. Moreover, cross-linked inulin
404
prepared through this novel method could have significant application potential for
405
cosmetic gels and drug delivery carriers. Currently, further research has been done on
406
specific application of CL-In used as a stabilizer in set yoghurt processing.
407
Acknowledgments
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This work was financially supported by the special project for people's livelihood
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of Chongqing municipal science and technology commission [cstc2015shmszx0367];
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and national natural science foundation of China [31471581].
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References
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Barclay, T., Ginicmarkovic, M., Cooper, P., & Petrovsky, N. (2010). Inulin - a versatile polysaccharide with multiple pharmaceutical and food chemical uses.
414
Journal of Excipients & Food Chemicals, 1(3), 27 - 50.
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413
Balthazar C. F., Santillo, A., Figliola, L., Silva, H.L.A., Esmerino, E.A., Freitas, M. Q.,
416
et al. (2018a). Sensory evaluation of a novel prebiotic sheep milk strawberry
417
beverage. LWT - Food Science and Technology, 98, 94–98.
418
https://doi.org/10.1016/j.lwt.2018.08.017.
M AN U
SC
415
Balthazar, C.F., Silva, H.L.A., Cavalcanti, R.N., Esmerino, E.A., Cappato, L.P., Abud,
420
Y. K. D., et al. (2017). Prebiotics addition in sheep milk ice cream: A rheological,
421
microstructural and sensory study. Journal of Functional Foods, 35, 564–573.
422
http://dx.doi.org/10.1016/j.jff.2017.06.004.
Balthazar, C. F., Silva, H. L. A., Esmerino, E. A., Rocha, R. S., Moraes, J., Carmo, M.
EP
423
TE D
419
A.V., et al. (2018b). The addition of inulin and Lactobacillus casei 01 in sheep
425
milk ice cream. Food Chemistry, 246, 464–472.
426 427
AC C
424
https://doi.org/10.1016/j.foodchem.2017.12.002.
Bohm, A., Kaiser, I., Trebstein, A., & Henle, T. (2005). Heat-induced degradation of
428
inulin. European Food Research & Technology, 220, (5-6), 466-471.
429
https://doi.org/10.1007/s00217-004-1098-8. 22
ACCEPTED MANUSCRIPT 430
Canbulat, Z., & Ozcan, T. (2015). Effects of Short‐Chain and Long‐Chain Inulin on the Quality of Probiotic Yogurt Containing Lactobacillus rhamnosus. Journal
432
of Food Processing & Preservation, 39 (6), 1251–1260.
433
https://doi:10.1111/jfpp.12343.
436
University Press.
SC
435
Doi, M. & Edwards, S. F. (1986). The theory of polymer dynamics. London: Oxford
Dan A., Ghosh S., & Moulik S. P. (2010). Physicochemical studies on the biopolymer
M AN U
434
RI PT
431
437
inulin: a critical evaluation of its self-aggregation, aggregate-morphology,
438
interaction with water, and thermal stability. Biopolymers, 91 (9), 687-699.
439
http://dx.doi.org/10.1002/bip.21199.
Freitas, R. A., Gorin, P. A.J., Neves, J., & Sierakowski, M. R. (2003). A rheological
TE D
440
description of mixtures of a galactoxyloglucan with high amylose and waxy corn
442
starches. Carbohydrate Polymers, 51(1), 25 - 32.
443
http://dx.doi.org/10.1016/S0144-8617(02)00095-4.
445 446
Ferry, J. D. (1980). Viscoelastic properties of polymers (3rd ed.). New York: John
AC C
444
EP
441
Wiley & Sons.
García, P., Vega, J., Jimenez, P., Santos, J. & Robert, P. (2013). Alpha-tocopherol
447
microspheres with cross-linked and acetylated inulin and their release profile in a
448
hydrophilic model. European Journal of Lipid Science & Technology, 115(7), 23
ACCEPTED MANUSCRIPT 449 450
811-819. https://doi.org/10.1002/ejlt.201200109.
García, P., Vergara, C. & Robert, P., (2015). Release Kinetic in Yogurt from Gallic Acid Microparticles with Chemically Modified Inulin. Journal of Food Science,
452
80(10), 2147-2152. http://dx.doi.org/10.1111/1750-3841.13001.
RI PT
451
Glibowski, P., & Bukowska, A. (2011). The effect of pH, temperature and heating
454
time on inulin chemical stability. Acta Scientiarum Polonorum: Technologia
455
Alimentaria, 10 (2), 188-214.
M AN U
456
SC
453
Gibson, G. R., Hutkins, R., Sanders, M. E., Prescott, S. L., Reimer, R. A., Salminen, S. J., et al. (2017). The International Scientific Association for Probiotics and
458
Prebiotics ISAPP consensus statement on the definition and scope of prebiotics.
459
Nature Reviews Gastroenterology & Hepatology, 14, 491–502.
460
TE D
457
Guimarães, J. T., Silva, E. K., Alvarenga, V. O., Costa, A., Cunha, R. L., Freitas, M. Q., et al. (2018a). Physicochemical changes and microbial inactivation after
462
high-intensity ultrasound processing of prebiotic whey beverage applying
463
different ultrasonic power levels. Ultrasonics – Sonochemistry, 44, 251–260.
AC C
464
EP
461
https://doi.org/10.1016/j.ultsonch.2018.02.012.
465
Guimarães, J. T., Silva, E. K., Costa, A. L. R., Cunha, R. L., Freitas, M. Q., Meireles,
466
M. A. A., et al. (2018b). Manufacturing a prebiotic whey beverage exploring the
467
influence of degree of inulin polymerization. Food Hydrocolloids, 77, 787-795.
24
ACCEPTED MANUSCRIPT 468 469
https://doi.org/10.1016/j.foodhyd.2017.11.021.
Hong Y., Wu Y., Liu G. & Gu Z. (2015) Effect of amylose on pasting and rheological properties of corn starch/xanthan blends. Starch/Stärke, 67, 98–106.
471
http://dx.doi.org/10.1002/star.201400126.
472
RI PT
470
Kim, Y., Faqih, M.N., & Wang, S.S. (2001). Factors affecting gel formation of inulin. Carbohydrate Polymers, 46 (2), 135-145.
474
https://doi.org/10.1016/S0144-8617(00)00296-4.
M AN U
475
SC
473
Luo, D., Li, Y., Xu, B, Ren, G., Li, P., Li, X., et al. (2017). Effects of inulin with different degree of polymerization on gelatinization and retrogradation of wheat
477
starch. Food Chemistry, 229, 35–43.
478
http://dx.doi.org/10.1016/j.foodchem.2017.02.058.
479
TE D
476
Liu, Z., Dong, Y., Men, H., Jiang, M., Tong, J. & Zhou, J. (2012). Post-crosslinking modification of thermoplastic starch/PVA blend films by using sodium
481
hexametaphosphate. Carbohydrate Polymers, 89 (2), 473-477.
482
http://dx.doi.org/10.1016/j.carbpol.2012.02.076.
484
AC C
483
EP
480
Li, S.P., Hu, T., Chen, Y.L., Zheng, C.Y., Liu, T., Ma, G.H., et al. (2010). Cross-linked inulin as a potential plasma expander: Biochemical properties and physiological
485
characterization in a rabbit model. Carbohydrate Polymers, 82(4), 1054-1060.
486
https://doi.org/10.1016/j.carbpol.2010.06.018.
25
ACCEPTED MANUSCRIPT 487 488 489
Miller, G.L. (1959). Use of DinitrosaIicyIic acid reagent for determination of reducing sugar. Analytical Chemistry, 31(3), 426-428.
Naskar, B., Dan A., Ghosh S., & Moulik S. P. (2010). Characteristic physicochemical features of the biopolymer inulin in solvent added and depleted states.
491
Carbohydrate Polymers, 81, 700–706.
492
http://dx.doi.org/10.1016/j.carbpol.2010.03.041.
SC
493
RI PT
490
Naskar B., Dan A., Ghosh S., & Moulik S. P. (2010). Viscosity and Solubility Behavior of the Polysaccharide Inulin in Water, Water plus Dimethyl Sulfoxide,
495
and Water plus Isopropanol Media. Journal of Chemical & Engineering Data,
496
55(7), 2424-2427. http://dx.doi.org/10.1021/je900834c.
Olivi-Tran, N., Botet, R., & Cabane, B. (1998). Monte Carlo simulations of colloidal
TE D
497
M AN U
494
dispersions under shear. Physical Review E, 57 (57), 1997-2003.
499
http://dx.doi.org/10.1103/PhysRevE.57.1997.
501 502 503
Pawel, G., & Adam, W. (2008). Effect of thermochemical treatment on the structure of inulin and its gelling properties. International Journal of Food Science &
AC C
500
EP
498
Technology, 43(11), 2075-2082. http://dx.doi.org/10.1111/j.13652621.2008.01825.x.
504
Paula, R.C.M. & Rodrigues, J.F. (1995). Composition and rheological properties of
505
cashew tree gum, the exudate polysaccharide from Anacardium occidentale L.
26
ACCEPTED MANUSCRIPT 506
Carbohydrate Polymers, 26 (95), 177–181.
507
https://doi.org/10.1016/0144-8617(95)00006-S.
508
Palma, M., García, P., & Márquez, R. G., (2014). Vergara, C., Robert, P. Release kinetics of flavonoids in methyl linoleate from microparticles designed with
510
inulin and channelizing agent. Food Research International, 64, 99 – 105.
511
http://dx.doi.org/10.1016/j.foodres.2014.05.064.
SC
512
RI PT
509
Ren, L., Jiang, M., Wang, L., Zhou, J., & Tong, J. (2012). A method for improving dispersion of starch nanocrystals in water through crosslinking modification with
514
sodium hexametaphosphate. Carbohydrate Polymers, 87(2), 1874-1876.
515
https://doi.org/10.1016/j.carbpol.2011.08.070.
Shoaib M., Shehzad A., Omar M., Rakha A., Raza H., Sharif H.R., et al. (2016).
TE D
516
M AN U
513
Inulin: Properties, health benefits and food applications. Carbohydrate Polymers,
518
147, 444-454. http://dx.doi.org/10.1016/j.carbpol.2016.04.020.
520 521 522 523 524
Tong, Y., Liu, T. Veeramani, S., & Chung, T. (2002). Bulk Viscosity and Its Unstable Behavior upon Storage in Polyimide Precursor Solutions. Industrial &
AC C
519
EP
517
Engineering Chemistry Research, 41(17), 4266 - 4272. http://dx.doi.org/10.1021/ie020159f.
Vervoort L., Mooter G. V. d., Augustijns P., Busson R., Toppet S., & Kinget R. (1997) Inulin hydrogels as carriers for colonic drug targeting: I. Synthesis and
27
ACCEPTED MANUSCRIPT 525
characterization of methacrylated inulin and hydrogel formation. Pharmaceutical
526
Research, 14 (12), 1730-1737. http://dx.doi.org/10.1023/A:1012179813102.
Wang Z., Gu Z., Li Z., Hong Y., & Cheng L. (2013). Effects of urea on freeze–thaw
528
stability of starch-based wood adhesive. Carbohydrate Polymers, 95, 397- 403.
529
https://doi.org/10.1016/j.carbpol.2013.02.009.
Wang N., Fu Q., & Yang G. (2012). Determination of the solubility, dissolution
SC
530
RI PT
527
enthalpy and entropy of icariin in water, ethanol, and methanol. Fluid Phase
532
Equilibria, 324, 41– 43. http://dx.doi.org/10.1016/j.fluid.2012.03.022.
533
M AN U
531
Zhang, T., Tian, Y., Jiang, B., & Ming, M. (2014). Purification, preliminary structural characterization and in vitro antioxidant activity of polysaccharides from
535
Acanthus ilicifolius. LWT - Food Science and Technology, 56(1), 9-14.
536
https://doi.org/10.1016/j.lwt.2013.11.010.
Zhou J., Zhang J., Ma Y., & Tong J. (2008). Surface photo-crosslinking of corn starch
EP
537
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534
sheets. Carbohydrate Polymers, 74, 405 - 410.
539
http://dx.doi.org/10.1016/j.carbpol.2008.03.006.
540 541
AC C
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Zhang, F., Fang, L., Wang, C., Shi, L., Chang, T., Yang, H., & Cui, M. (2013). Effects of starches on the textural, rheological, and color properties of surimi–beef gels
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with microbial tranglutaminase. Meat Science, 93, 533–537.
543
http://dx.doi.org/10.1016/j.meatsci.2012.11.013.
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Table 1 Average Mw, average DP, intrinsic viscosity, and water solubility of S-In, L-In, CS-In and CL-In.
Average
Average DP
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Intrinsic
Solubility (g/100g)
Mw (Da)
40℃
60℃
80℃
26.86±0.82aD
40.82±0.31aC
46.79±0.21aB
49.62±0.88aA
8.30±0.48bD
14.61±0.13bC
21.36±0.06bB
32.35±0.07bA
877±21d
4.30±0.16d
1.53±0.11d
CS-In
1295±32c
6.88±0.19c
2.43±0.14c
L-In
2022±53b
11.37±0.33b
4.85±0.20b
1.97±0.16cD
7.68±0.20cC
11.76±0.25cB
20.70±0.93cA
CLNI
2626±58a
15.10±0.36a
1.21±0.02cC
4.08±0.10dB
7.39±0.16dA
7.68±0.01dA
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viscosity (dL/g)
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6.78±0.53a
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Mean values followed by the different letter (a−d) in each column are significantly different (p ≤ 0.05). Mean values followed by the different
546
letter (A−D) for temperature in each row are significantly different (p ≤ 0.05). 29
ACCEPTED MANUSCRIPT Table 2 Power law model-fitted parameters.
5%
0.0073
10%
n
R2
0.1528
0.3393
0.9718
0.0069
0.1134
0.3918
0.9759
20%
0.0088
0.2823
30%
0.0096
0.3019
40%
0.0115
0.3231
50%
0.0114
0.3283
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(Pa•s )
5%
0.0079
0.198
0.3
0.9926
10%
0.0097
0.2095
0.3337
0.9663
0.2467
0.9723
0.2508
0.9636
0.2756
0.9336
0.2702
0.9442
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n
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L-In
0.0339
0.7737
0.3209
0.9604
0.5376
29.0582
0.1336
0.9692
1.083
62.1779
0.1205
0.9754
3.093
170.4428
0.1294
0.9926
0.0077
0.1959
0.2972
0.9828
10%
0.0208
0.4444
0.3353
0.971
20%
0.0207
0.4533
0.3297
0.9753
30%
0.0223
0.5776
0.2935
0.9697
40%
0.0205
0.516
0.2997
0.9726
50%
0.0286
0.7474
0.2912
0.9624
5%
0.0115
0.6878
0.112
0.9655
10%
0.0123
0.5904
0.1593
0.9312
20%
0.0351
1.16
0.2405
0.9314
30%
0.5953
37.2853
0.1016
0.976
40%
1.6531
117.1904
0.0747
0.9583
50%
4.0509
218.8529
0.1337
0.9762
30% 40% 50%
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CL-In
K
(Pa•s)
S-In
CS-In
η100
Concentration (%)
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Fig. Captions
549
Fig.1 IR spectra of CL-In (a), L-In (b), CS-In (c) and S-In (d).
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Fig.2 SEM images of S-In powder (a), L-In powder (b), CS-In powder (c) and CL-In
552
powder (d).
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Fig.3 Thermal stability of four kinds of inulin (a), acid stability of four kinds of inulin
555
(b). (Coordinate values followed by the different letter (A−C) for different inulin at
556
same condition are significantly different (p ≤ 0.05). Coordinate values followed by
557
the different letter (a−f) for each inulin at different conditions are significantly
558
different (p ≤ 0.05)).
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Fig.4 The moisture absorption content of four kinds of inulin at 81 % RH (a), and 92 %
561
RH (b). (Coordinate values followed by the different letter (A−D) for different inulin
562
at same time are significantly different (p ≤ 0.05). Coordinate values followed by the
563
different letter (a−c) for each inulin at different time are significantly different (p ≤
564
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Fig.5 The viscoelastic properties of the steady shear measurements for S-In (a), CS-In
567
(b), L-In (c) and CL-In (d) dispersions of 5%, 10%, 20%, 30%, 40%, and 50% (w/v)
568
at a temperature of 25 °C.
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Fig.6 The viscoelastic properties of the steady shear measurements for S-In, L-In,
571
CS-In and CL-In dispersions of 40% (w/v) at a temperature of 25 °C (a); Temperature
572
dependence of viscosity for S-In, L-In, CS-In and CL-In dispersions of 40 % (w/v) at
573
a steady shear rate of 50 s-1 (b); The viscoelastic properties of dynamic frequency
574
sweep measurements for the 40% dispersions of inulin at a temperature of 25 °C (c);
575
The viscoelastic properties of dynamic frequency sweep measurements (values of
576
complex modulus (G*) vs. frequency) for the 40% dispersions of S-In, L-In, CS-In
577
and CL-In at a temperature of 25 °C (d).
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ACCEPTED MANUSCRIPT Research highlights (1) Cross-linked inulin was prepared using sodium hexametaphosphate as cross-linker.
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(2) Polymerization degree has marked effects on physicochemical properties of cross-linked inulin.
(3) Cross-linked inulin exhibited as a pseudoplastic fluid and more solid viscoelastic
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properties.