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Effects of soluble dietary fiber on the crystallinity, pasting, rheological, and morphological properties of corn resistant starch
Accepted Manuscript Effects of soluble dietary fiber on the crystallinity, pasting, rheological, and morphological properties of corn resistant starch Xiane Liu, Suchen Liu, Huiting Xi, Junjun Xu, Danwen Deng, Ganhui Huang PII:
S0023-6438(19)30070-2
DOI:
https://doi.org/10.1016/j.lwt.2019.01.059
Reference:
YFSTL 7801
To appear in:
LWT - Food Science and Technology
Received Date: 30 November 2018 Revised Date:
28 January 2019
Accepted Date: 29 January 2019
Please cite this article as: Liu, X., Liu, S., Xi, H., Xu, J., Deng, D., Huang, G., Effects of soluble dietary fiber on the crystallinity, pasting, rheological, and morphological properties of corn resistant starch, LWT - Food Science and Technology (2019), doi: https://doi.org/10.1016/j.lwt.2019.01.059. 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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Effects of soluble dietary fiber on the crystallinity,
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pasting, rheological, and morphological properties of corn resistant starch
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Xiane Liu, Suchen Liu, Huiting Xi, Junjun Xu, Danwen Deng, Ganhui Huang*,
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State Key Laboratory of Food Science and Technology, Nanchang University,
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Nanchang, 330047, China
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* Corresponding author: Professor Ganhui Huang, PhD, State Key Laboratory of
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Food Science and Technology, Nanchang University, No. 235 Nanjing East Road,
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Nanchang 330047, Jiangxi, China.
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Tel: +86-136 0708 8530;
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E-mail address: (G. Huang) [email protected]
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Abstract In this research, corn resistant starch (CRS) was mixed with four kinds of soluble
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dietary fibers (chitosan, flaxseed gum, xanthan gum, and konjac gum). The pasting and
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rheological properties, microstructure, and X-ray diffraction spectrum of the mixed
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system were investigated by rapid viscosity analyzer (RVA), rheometer, scanning
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electron microscopy (SEM), and X-ray diffractometer (XRD). The pasting curves
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showed that the addition of chitosan could reduce the viscosity of CRS paste, while the
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flaxseed gum, xanthan gum and konjac gum increased the viscosity. All complex
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systems had shear thinning properties in the rheological steady flow experiments.
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Soluble dietary fibers significantly increased the value of viscosity coefficient (K) of the
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CRS, however, the value of flow characteristic index (n) was decreased with increasing
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concentration of soluble dietary fibers. Soluble dietary fibers addition resulted in higher
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storage modulus and loss modulus (G' and G'') of CRS paste, as well as giving rise to
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high viscoelasticity. SEM confirmed that the addition of soluble dietary fibers made the
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starch granules more easily aggregated in the mixed systems. X-ray diffraction spectrum
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analysis showed that the addition of soluble dietary fibers did not change the B and V
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type crystalline pattern of CRS, and both the concentrations and types of soluble dietary
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fibers had significant effects on the crystallinity of mixed systems. This study reported
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four mixtures with CRS and provided useful information for functional food.
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Keywords: resistant starch, soluble dietary fiber, pasting, rheology, morphology
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1. Introduction With the development of food nutriology, resistant starch is widely used in food
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processing as a new type of dietary fiber. On the one hand, resistant starch in food
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industry can increase the content of dietary fiber, overcome some of the deficiencies of
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traditional dietary fiber on the taste, formability and texture of the product, simplify the
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food processing and make food quality better (Marlatt et al., 2017). On the other
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hand, resistant starch containing high dietary fiber is often used to develop new food
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supplements as functional factors, as it can prevent the gastrointestinal diseases and
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cardiovascular disease, reduce postprandial glycemic and insulinemic responses, modify
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colonic micro-florato form short-chain fatty acids, and promote bacterial growth and
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mineral absorption (Brouns, Kettlitz, & Arrigoni, 2002; Kendall et al., 2008;
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Fuentes-Zaragoza, Riquelme-Navarrete, Sánchez-Zapata, & Pérez-Álvarez, 2010).
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Soluble dietary fiber is often used in starch-based product as thickener and
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emulsifier to control the flow of water and improve the quality and storage performance.
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Meanwhile, the effects of soluble dietary fiber on starch mainly depend on the sources,
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species, molecular weight, and compounding ratio of soluble dietary fiber. Extracted
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from different sources, chitosan, flaxseed gum, xanthan gum and konjac gum have
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different ionic properties and molecular weights and are commonly used as additives in
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food processing. Chitosan, exploited from shrimp and crabs, is the only positively
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charged alkaline cationic linear polysaccharide in nature (Rinaudo, 2007). Josiane et al.,
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(2016) pointed that the presence of chitosan hindered the formation of starch gel to
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some extent, and the influences of chitosan on starch were mainly attributed to the
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competition for water available between biopolymers, thus delaying granule swelling
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and decreasing the amount of leached amylose for gel formation. Flaxseed gum,
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neutral linseed polysaccharide (Ziolkovska, 2012). Wang et al., (2008) reported that the
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apparent viscosities and the values of G' and G'' of samples increased with flaxseed gum
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addition increasing, and the flaxseed gum-maize starch mixtures had a gel-like structure.
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Xanthan gum, obtained from the bacterium Xanthomonas campestris, is a microbial
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polysaccharide with a primary structure having repeated pentasaccharide units. Xanthan
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gum is broadly used as a food additive in food industry such as stabilizer and thickener
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because of its good water solubility, high viscosity, and pseudoplastic rheological
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properties (Palaniraj, & Jayaraman, 2011; Garcíaochoa, Santos, Casas, & Gómez, 2000).
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The ddition of xanthan gum in starch was widely reported to control and improve the
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pasting and rheological properties of starch (Bemiller, 2011; Nawab, Alam, Haq, &
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Hasnain, 2016; Heyman, Vos, Depypere, Meeren, & Dewettinck, 2014; Heyman, Vos,
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Meeren, & Dewettinck, 2014). Konjac gum is a non-ionic water-soluble neutral
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polysaccharide extracted from the underground tuber of herbaceous konjac. It is rich in
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hydroxyl and carbonyl groups, and has good thickening, emulsification, film formation
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and stability (Zhang, Chen, & Yang, 2014). Konjac gum was mainly used to
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synergistically interact with certain gums (Brenner, Wang, Achayuthakan, Nakajima, &
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Nishinari, 2013; Cui, Eskin, Wu, & Ding, 2006; Lin, & Huang, 2003) and replace fat
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(Dai, Jiang, Corke, & Shah, 2018).
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Previous studies reported that mixtures of starch/soluble dietary fiber were mixed
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with native starch and soluble dietary fiber, while limited information has been covered
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on the mixtures properties of soluble dietary fiber with resistant starch. In this study, the
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effects of four different kinds of soluble dietary fiber on the crystallinity, pasting,
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rheological, and morphological properties of corn resistant starch were investigated by
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and X-ray diffractometer (XRD).
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2. Materials and methods
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2.1. Materials
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The chitosan (CT), flaxseed gum (FG), xanthan gum (XG), and konjac gum (KG)
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were of food grade and obtained from Hebei Baiwei Biotechnology Corporation
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(Handan, China). Corn resistant starch (CRS) (total dietary fiber content: 65.40%;
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resistant starch content: 40.95 ± 1.26%) was acquired from American National Starch
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Corporation (USA). Glucoamylase (100,000 U/ml), and α-amylase (100,000 U/ml) were
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purchased from Aladdin Reagent Corporation (Shanghai, China). All other chemicals
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and reagents used in this study were of analytical grade.
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2.2. Determination of resistant starch (RS) content
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The RS content was determined by means of an enzymatic method (AOAC
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2002.02) with a modification. 100 mg CRS (dry basis) was weighed accurately, and
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suspended in distilled water. Then, the suspensions were incubated with α-amylase (500
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U/g) in a water bath at 93 °C and pH 6.5 for 30 min after aging. The non-resistant starch
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was solubilised and hydrolyzed to glucose by the action of enzyme during the time. The
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reaction was terminated by mixing it with anhydrous ethanol and the indigested
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resistant starch was recovered by centrifugation (4800 rpm, 10 min). Then, the
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centrifuged RS was suspended in distilled water. Subsequently, Glucoamylase (5000
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U/g) was added to the above prepared paste, and the paste was incubated in a water bath
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at 60 °C for 30 min after adjusting the pH to 4.5 with a hydrochloric acid solution (1
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activity. The suspensions were centrifuged at 4800 rpm for 15 min by using a centrifuge
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(TGL-15B, Shanghai Anting Scientific Instrument Factory, Shanghai, China). The
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pellet containing the RS was purified with ethanol and solubilized with 2 mol/L KOH.
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The concentration of RS was measured at 510 nm in a spectrophotometer (Shanghai
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Jingke Industrial Co., Ltd, Shanghai, China). Resistant starch content was calculated as
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the amount of glucose × 0.9. The results were obtained in analytical triplicate and are
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presented as the mean ± the standard deviation.
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2.3. Preparation of suspensions of CRS/SDF
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CRS (60.0 mg/mL) with different concentrations of SDF (0 mg/mL; 0.5 mg/mL;
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1.0 mg/mL; 2.0 mg/mL; 3.0 mg/mL; 5.0 mg/mL) mixtures were prepared as follows.
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Briefly, CT, FG, XG, and KG powder were firstly dissolved in distilled water with
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continuous stirring for 30 min with 150 rpm, respectively. Then the CRS (60.0 mg/mL)
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was dispersed into CT, FG, XG, and KG solutions by magnetic stirring for 10 min with
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150 rpm at room temperature to prepare the mixed suspensions. All suspensions were
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stored for 3 min at room temperature to perform the following determinations.
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2.4. Pasting properties
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Pasting properties of CRS and the mixtures of CRS/CT, CRS/FG, CRS/XG, and
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CRS/KG suspensions were determined by using Rapid Visco Analyzer (RVA, Newport
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Scientific, NSW, Australia). The mixed samples (25 mL) were prepared as described in
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section 2.3. The slurries were poured into aluminium canisters and manually stirred
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using plastic paddles for 20-30 s before insertion into the RVA. The RVA Standard 1
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viscosity (TV), breakdown viscosity (BV), final viscosity (FV), setback viscosity (SV)
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and peak time (PeT) were calculated by RVA system software. And the pasting curve of
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samples were obtained by means of RVA program. The hot paste of samples were
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cooled to room temperature, and stored in the refrigerator (5 °C) for 24 h to perform the
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following determinations.
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2.5. Rheological measurements
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All samples were prepared by RVA (section 2.4) and evaluated using a rheometer
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(ARES-G2, TA Instruments Inc., USA) with a stainless steel parallel plate (40 mm
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diameter, 0.5 mm gap). The relationship between the apparent viscosity and shear stress
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of samples was measured in the shear rate ranging from 1 to 1000 s-1 at 25 °C. The shear
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stress data was fitted to the power law model expressed by equation (1) (Sun, & Yoo,
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2015; Liu et al., 2018):
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τ = Kγn
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where τ is shear stress (Pa), K is consistency coefficient (Pa·sn), γ is shear rate (s-1), and n is flow behaviour index, R2 is determination coefficient (dimensionless).
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The oscillatory rheological measurements of samples were performed to obtain the
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storage modulus (G'), loss modulus (G''), and loss tangent (tan δ= G″/ G′) at the angular
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frequency sweeps ranging from 0.1 to 126 rad/s in strain 1.0% at 25 °C.
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2.6. Scanning electron microscopy (SEM)
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All samples were obtained as described in section 2.4 and freeze-dried in the
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-80 °C lyophilizer (Labconco Co., USA). The dried samples were finely ground, and
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coated with a thin layer of gold to avoid charging under the electron beam (Garcia-Diaz,
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sample at magnification of 1000× by using SEM (SEM, JSM6701F, Japan) with
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accelerating potential of 5.0 kV.
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2.7. X-ray diffraction (XRD)
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The powder was obtained as described in section 2.6 and measured in an X-ray
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diffractometer (D8 Advance; Bruker Inc., Germany) by using Cu Kα at a speed of
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10 °/min (Koteswara, Vidya, & Haripriya, 2015). All samples were scanned through the
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diffraction angle of 2θ from 5 ° to 60 ° at a voltage of 40 kV and filament current of 40
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mA. The area under the crystalline peak curve and the area under the amorphous peak
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were measured with Jade 6.0 software and the relative crystallinity (RC) was estimated
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with Jade 6.0 software according to the following formula (2) :
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AC × 100 % AC + Aα
where AC is the area of the crystalline peak and Aα is the area of the amorphous peak.
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2.8. Statistical analysis
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All measurements were made in triplicate for each sample. All of the graphs were
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plotted by using OriginPro 8.0 software (Stat-Ease Inc., Minneapolis, USA). One-way
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analysis of variance(ANOVA) and the mean separations were analyzed by Tukey’s
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HSD test (p < 0.05) with the SPSS 22.0 Statistical Software Program.
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3. Results and discussion
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3.1. Pasting properties The pasting of starch is the swelling of starch granules at a certain temperature to
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destroy the hydrogen bonds associated with starch granules in the crystallization and the
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amorphous zone (Chen, et al., 2015). The pasting profiles of mixtures of corn resistant
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starch (CRS) and different soluble dietary fiber (SDF) are presented in Fig. 1. The
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pasting parameters of mixtures are shown in Table 1.
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CRS had a low viscosity during pasting due to the fact that high amylose content
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could limit the swelling of starch (Tester & Morrison, 1990). The addition of flaxseed
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gum (FG), xanthan gum (XG), and konjac gum (KG) could increase the apparent
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viscosity of CRS during the pasting process, and the KG had the most significant effect
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on CRS. The increase in viscosity was mainly attributed to the reduction in available
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water molecules for starch granules caused by the competition of water absorption from
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high amount of FG, XG, and KG (Bemiller, 2011). CT could slightly decrease the
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viscosity of CRS. The different behavior between CT and KG was obviously visible.
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This might be due to the fact that CT is the only positively charged alkaline cationic
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polysaccharide in nature, which could limit the swelling of starch granules during the
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pasting. In addition, viscosity increase of CRS resulting from addition of FG, XG, and
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KG were probably due to a higher molar mass (Singh, Gevekeal, & Yadav, 2017). The
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effects of different SDF on the viscosity of CRS were slight at a level of 0.5 - 1.0
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mg/mL during pasting, however, that of 3.0 - 5.0 mg/mL SDF was significant. It
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indicated that the high concentration of FG, XG, and KG played an important role in
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starch swelling and could form hydration film by coating around the starch granules to
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it demonstrated that the factors which could affect viscosity of mixtures were complex,
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and the pasting properties were strongly dependent on the type of SDF for given
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SDF/CRS ratio.
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As shown in Table 1, compared to CRS, the addition of SDF (without CT)
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significantly (p < 0.05) increased the peak viscosity (PV), trough viscosity (TV),
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breakdown viscosity (BV), final viscosity (FV), and setback viscosity (SV). The
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opposite result has been reported by Qiu, Yadav, Chen, Liu, Tatsumi, & Yin. (2015),
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which suggested that values of PV and BV of native maize starch decreased with the
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addition of corn fiber gum (CFG). The value of PV represented the point of maximum
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granular swelling and reflected water absorption capacity of starch granules, and the
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increase of PV on starch mixtures was often reported in polysaccharides/starch (Kong,
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Zhu, Sui, & Bao, 2015; Bemiller, 2011). The increase in the value of PV might be due
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to an increased effective molecular size, resulting from physical or chemical interaction
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between the RS and SDF (Liu, Nam, & Cui, 2003). BV values, calculated with the
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magnitudes of PV and TV of samples, reflects the stability of starch paste. The addition
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of KG significantly increased the value of BV of CRS from 4.67 to 244.33 mPa.s,
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suggesting that KG could promote the fragmentation of starch granules during heating
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process. FV values represent the gel or paste forming capability of starch after cooking
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and cooling, which were changed between 4.67 and 1000.37 mPa.s at a level of 5.0
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mg/mL addition. SV represents the differences between TV and FV, and the addition of
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FG, XG and KG significantly increased SV of CRS (p < 0.05) in the order of KG >
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FG > XG, which indicated that the addition of FG, XG and KG markedly affected the
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retrogradation of CRS at the cooling stage (Zhou, Zhang, Chen, & Chen, 2017).
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3.2. Rheological properties
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3.2.1. Steady flow The flow behaviors of mixtures under steady shear conditions at 25 °C are
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presented in Fig. 2. The consistency coefficient (K), flow behavior index (n), and
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determination coefficient (R2) for each flow curve were summarized in Table 2. As
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shown in Fig. 2, the viscosity decreased with the shear rate increasing, illustrating that
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the internal structure of the mixed systems was destroyed or formed a new structure and
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all samples exhibited shear thinning behavior under the current experimental conditions
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(Samutsri, & Suphantharika, 2012). The results in Table 2 demonstrated that the power
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law model was well fitted to the profile of rheological characteristics of all samples
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according to the value of R2 ranging from 0.9845 to 0.9999. The values of K of
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mixtures in the presence of FG, XG, and KG were higher than CRS alone, suggesting
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that the addition of FG, XG, and KG resulted in more resistance to flow (Kumar,
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Brennan, Zheng, & Brennan, 2018), which was consistent with the discussion in RVA
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(Table 1). In this study, the n value of CRS was 1.0435, which indicated that the CRS
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fluid was similar with Newtonian fluid. And, the SDF significantly (p < 0.05) decreased
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the value of n of CRS ranging from 0.1620 to 0.9223, suggesting that the mixed systems
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were the typical pseudoplastic fluid. The CRS/XG at a level of 5.0 mg/mL addition had
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the lowest n value, which indicated that the 5.0 mg/mL CRS/XG mixture could induce
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the formation of the strongest gel. Similar results were previously reported by Yuvaret,
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Piyada, & Manop, (2008), in which they suggested that XG had high shear stability, it
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could obviously promote re-association of damaged structure induced by high shear rate.
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The 5.0 mg/mL CRS/KG had the highest K, followed by XG, FG, and CT, respectively.
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3.2.2. Dynamic rheological properties The dynamic viscoelastic properties of sample had considerable significance in the
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practical application of processing performance and quality control. The loss modulus
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(G'') represents the viscous behavior of sample and the storage modulus (G') represents
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elastic behavior of sample. From Fig. 3, it can be seen that the storage modulus (G') of
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CRS was greater than its loss modulus (G'') during the entire frequency range,
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indicating that the 60.0 mg/mL CRS paste had a elastic behavior superior to viscous
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behavior (Chen, Tong, Ren, & Zhu, 2014; Herrera, Vasanthan, & Chen, 2016). It
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demonstrated that amylose is dominant in swelling of starch and high amylose content
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could increase the brittleness and strength of starch (Singh, Kaur, & Mccarthy. 2007).
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The storage modulus (G′) and loss modulus (G″) of mixtures were increased with the
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increasing of angular frequency (Fig. 3). The addition of SDF obviously increased the
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dynamic modulus (G′, G″) of CRS, which revealed that the addition of SDF influenced
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the structure of paste of CRS. In the case of adding CT, XG, and KG, the G′ was
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obviously higher than G″ and the dynamic modulus (G′, G″) were frequency-dependent.
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There was’t a crossover between G′ and G″ during the whole frequency range, which
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suggested that these mixed systems were typical weak gel classified by Clark &
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Ross-Murphy (1987) in rheology. Similar results were also reported in previous studies
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on composite system of tapioca starches and xanthan gum (Chaisawang, &
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Suphantharika, 2006). The addition of 0 - 2.0 mg/mL FG/CRS made mixtures with
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elastic behavior. However, at the concentration of 3.0 and 5.0 mg/mL FG/CRS, a
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crossover between the dynamic modulus (G′, G″) was observed in70.5 and 14.1 rad/s,
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respectively (Fig. 3B).
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3.3. Scanning electron microscopy (SEM) The particle morphology and surface characteristics of all mixtures are shown in
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Fig. 4. The results obtained by SEM illustrated that the shape of the CRS granules was
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sphere or oval, the surface was smooth with a slight roughness, and the size ranged from
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5 to 20 µm in length and from 5 to 10 µm in width. A similar result was observed by
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Mao, Lu, & Huang, et al. (2018) who studied the morphology of winged yam (Dioscorea
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alata L.) resistant starch granules. The addition of SDF had no effect on the shape of
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CRS granules, but the degree of aggregation of CRS granules was significantly affected.
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The aggregation degree of mixed systems became more pronounced as the amount of
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SDF increased. When added with different concentration of SDF in CRS, the
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arrangement of granules was out-of-order. In the case of adding FG, XG, and KG, most
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of the CRS were tightly wrapped by an adhering gum layer in the continuous phase as
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shown in Fig. 4. Moreover, the FG, XG, and KG could swell well which resulted in a
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significant (p < 0.05) increase in PV, TV, BV, FV, and SV during pasting as compared
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with those obtained form the addition of CT (Table 1). This might be due to the fact that
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FG, XG, and KG are hydrocolloids which could cross link with leached or gelatinized
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CRS. It is noteworthy that a protective layer was formed on the surface of CRS and the
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network structure was enhanced between the CRS and hydrocolloids with the increasing
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addition of hydrocolloids. The KG/CRS was the most dense aggregation with addition
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concentration of 5.0 mg/mL, followed by XG, and FG, respectively.
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3.4. X-ray diffraction (XRD)
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The X-ray diffraction patterns of all samples are presented in Fig. 5. It indicated
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CRS exhibited strong diffraction peaks at 5.6°, 7.4°, 13.2°, 17.2°, 20.1°, 22.2°, and
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13.2°~24.0°. The mixed systems exhibited diffraction peaks at 7.4°, 13.2°, 17.2°, 20.1°,
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22.2°, 23.4°, 25.5°, 23.9°, and 30.5° 2θ compared with CRS. X-ray diffraction patterns
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of all samples displayed a mixture of B and V-type, although some peaks disappeared
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and new peaks appeared, which suggested that the cross link of the mixed systems
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mainly occurred in the amorphous region (Tang, & Copelang, 2007). The intensity and
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peak width of the diffraction peak were related to the relative crystallinity (RC, %) of
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the crystallization region. The relative crystallinity (RC, %) of all samples was obtained
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by formula (2) and shown in Table 3. It illustrated that different concentrations and
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types of SDF had different effects on the RC (%) of CRS, which indicated that the
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effects of SDF on CRS were not unique but related to concentrations. The RC (%) of
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CRS/KG mixtures was the highest at a level of 5.0 mg/mL addition, followed by
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CRS/XG, CRS/FG, and CRS/CT, respectively. The effects of KG on the crystalline
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structure of CRS might be due to the reduction of amylose content in the amorphous
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region and the rearrangement of double helix structure of the amylopectin side chains
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(Israkarn, Nakornpanom, & Hongsprabhas, 2014).
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4. Conclusions
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In this study, the effects of soluble dietary fibers on corn resistant starch were
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evaluated by RVA, rheometer, SEM, and XRD. The viscosity of CRS significantly
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increased with the increase of amount of FG, XG and KG during the pasting, and konjac
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gum had the highest viscosity (1000.37 mPa.s), whereas chitosan had the lowest
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viscosity (1.67 mPa.s). At the addition of 3.0 and 5.0 mg/mL of FG, these mixtures
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presented a crossover between the dynamic modulus (G′, G″) at angular frequency of
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could improve the pasting, rheological and morphological properties, and konjac gum
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was the most effective. In general, this study will be useful for formulating desirable
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pasting, rheological properties, and microstructure, as well as designing and developing
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new RS-based products at high ratios of soluble dietary fibers.
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Acknowledgements
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The Graduate Innovative Special Fund Projects of Nanchang University (No.
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CX2017135) and the First Class Open Fund Projects of Food Science and Engineering
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of Zhejiang Province (JYTsp20142015) supported this study.
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Abbreviations
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CRS, corn resistant starch; SDF, soluble dietary fibers; CT, chitosan; FG, flaxseed gum;
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XG, xanthan gum; KG, konjac gum; RVA, viscosity analyzer; SEM, scanning electron
318
microscopy; XRD, X-ray diffraction; PV, TV, BV, FV, and SV, peak, trough,
319
breakdown, final, and setback viscosity; PeT, peak time; RC, relative crystallinity; G',
320
storage modulus; G'', loss modulus
321
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ACCEPTED MANUSCRIPT Table 1
PV (mPa.s)
TV (mPa.s)
BV (mPa.s)
FV (mPa.s)
SV (mPa.s)
PeT (min)
CRS
8.66 ± 0.94ab
3.67 ± 0.47a
4.67 ± 0.47a
5.67 ± 0.47a
2.00 ± 0.00a
1.07 ± 0.00a
0.5 CT
4.33 ± 0.47a
0.00 ± 0.00a
4.33 ± 0.47a
1.67 ± 0.47a
1.67 ± 0.47a
1.11 ± 0.06a
1.0 CT
4.00 ± 0.82a
0.00 ± 0.00a
4.67 ± 0.47a
1.67 ± 0.47a
2.33 ± 0.47a
1.07 ± 0.00a
2.0 CT
5.00 ± 0.00a
0.00 ± 0.00a
4.67 ± 0.47a
2.67 ± 0.47a
2.33 ± 0.47a
1.09 ± 0.03a
3.0 CT
5.33 ± 0.94a
0.67 ± 0.47a
5.00 ± 0.82a
3.33 ± 1.25a
3.00 ± 0.82a
1.13 ± 0.00a
5.0 CT
5.33 ± 0.47a
1.33 ± 0.47a
4.67 ± 0.47a
4.67 ± 0.47a
4.00 ± 0.82a
1.11 ± 0.06a
0.5 FG
9.00 ± 0.82ab
4.67 ± 0.47ab
4.67 ± 0.94a
7.33 ± 0.94ab
3.33 ± 0.47a
1.11 ± 0.06a
1.0 FG
9.67 ± 0.47ab
5.67 ± 0.47abc
4.00 ± 0.00a
9.33 ± 0.47abc
3.67 ± 0.47a
1.07 ± 0.00a
2.0 FG
16.33 ± 0.47ab
10.33 ± 0.47abcd
6.00 ± 0.82a
24.00 ± 0.82cd
13.67 ± 0.94abc
1.18 ± 0.16a
3.0 FG
37.67 ± 0.47e
18.00 ± 0.82d
9.33 ± 0.47ab
44.67 ± 1.25e
26.67 ± 1.25c
1.31 ± 0.21ab
5.0 FG
100.67 ± 2.49g
64.67 ± 5.44gh
18.67 ± 1.25bcd
119.00 ± 6.38g
51.00 ± 5.10d
1.67 ± 0.22bcd
0.5 XG
21.67 ± 1.70bc
20.33 ± 0.47de
2.33 ± 0.47a
21.33 ± 1.70bcd
2.33 ± 0.47a
1.11 ± 0.06a
1.0 XG
35.33 ± 3.86cde
30.67 ± 1.89ef
5.67 ± 0.94a
31.67 ± 1.89de
1.00 ± 0.00a
1.07 ± 0.00a
2.0 XG
68.33 ± 6.18f
57.00 ± 4.32g
13.00 ± 0.82abc
67.67 ± 3.30f
12.33 ± 2.36ab
1.40 ± 0.34abc
3.0 XG
118.67 ± 2.06h
86.33 ± 3.86i
29.00 ± 2.83d
106.33 ± 2.06g
17.33 ± 1.70bc
1.13 ± 0.05a
5.0 XG
221.67 ± 8.38j
199.00 ± 6.98k
26.00 ± 3.74d
221.00 ± 8.83i
25.33 ± 1.25bc
1.29 ± 0.13ab
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Sample
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Pasting properties of CRS (60.0 mg/mL), CRS/CT, CRS/FG, CRS/XG, and CRS/KG mixtures.
22.67 ± 4.50bcd
16.67 ± 3.40cd
8.33 ± 0.47ab
36.00 ± 4.55de
19.67 ± 1.70bc
1.16 ± 0.06a
37.00 ± 4.55de
16.33 ± 0.94bcd
21.67 ± 3.09cd
69.67 ± 1.25f
53.33 ± 0.47d
1.82 ±0.14cde
57.33 ± 3.40f
35.33 ± 2.06f
22.00 ± 1.41cd
187.67 ± 6.24h
153.00 ± 3.56e
1.89 ± 0.03de
3.0 KG
149.00 ± 9.63i
69.00 ± 5.89h
80.00 ± 5.10e
440.33 ± 6.94j
364.67 ± 13.02f
2.18 ± 0.07e
5.0 KG
363.33 ± 4.99k
152.33 ± 5.91j
244.33 ± 10.66f
1000.67± 8.18k
862.33 ± 4.50g
2.16 ± 0.20e
0.5 KG 1.0 KG 2.0 KG
Values are means ± SD of triplicates. Values in the same column with different superscript are significantly different (p < 0.05).
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Table 2 Steady flow parameters for CRS (60.0 mg/mL), CRS/CT, CRS/FG, CRS/XG, and
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CRS/KG mixtures. R2
K
n
CRS
0.0010a
1.0435u
0.9956
0.5 CT
0.0152g
0.9223o
0.9973
1.0 CT
0.0188h
0.9861t
0.9990
2.0 CT
0.0032b
0.9598s
0.9995
3.0 CT
0.0038c
0.9505r
0.9856
5.0 CT
0.0062e
0.9452q
0.9988
0.5 FG
0.0050d
0.9266p
0.9962
1.0 FG
0.0133f
0.8876n
0.9999
2.0 FG
0.0855k
0.7031l
0.9999
3.0 FG
0.3442m
0.5652k
0.9991
5.0 FG
1.9601p
0.4214i
0.9954
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0.0671j
0.5623j
0.9901
1.0 XG
0.2341l
0.4209h
0.9845
2.0 XG
0.9850o
0.2521f
0.9896
3.0 XG
2.3843q
0.1765c
0.9848
5.0 XG
5.2080s
0.1620a
0.9920
0.5 KG
0.0287i
0.7089m
0.9905
1.0 KG
0.4896n
0.4124g
0.9898
2.0 KG
4.0578r
0.2365e
0.9804
3.0 KG
13.1255t
0.1889d
0.9806
5.0 KG
43.1247u
0.1685b
0.9805
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0.5 XG
Values in the same column with different superscript are significantly different (p < 0.05). K is consistence coefficient; n is flow behavior index; R2 is determination coefficient.
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Table 3 The relative crystallinity of CRS (60.0 mg/mL), CRS/CT, CRS/FG, CRS/XG, and
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CRS/KG mixtures. CRS/CT
CRS/FG
CRS/XG
CRS/KG
0
35.98%
35.98%
35.98%
35.98%
0.5
35.81%
34.77%
33.48%
35.06%
1.0
34.85%
37.34%
34.62%
36.33%
2.0
34.33%
37.38%
3.0
31.45%
38.68%
5.0
30.19%
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Concentration
37.54%
38.32%
38.89%
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37.65%
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38.96%
3
38.84%
39.16%
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3.0 mg/mL SDF; ★ 5.0 mg/mL SDF). Fig. 2 Steady flow curves of CRS/CT (A), CRS/FG (B), CRS/XG (C), and CRS/KG (D) mixtures. (■ no SDF; ● 0.5 mg/mL SDF; ▲ 1.0 mg/mL SDF; ◆ 2.0 mg/mL SDF;
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3.0 mg/mL SDF; ★ 5.0 mg/mL SDF).
Fig. 3 Storage modulus (G′) and loss modulus (G″) of CRS/CT (A), CRS/FG (B),
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CRS/XG (C), and CRS/KG (D) mixtures as a function of frequency. The solid symbols represent the storage modulus (G′) and the open symbols represent the loss modulus (G″). (■ no SDF; ● 0.5 mg/mL SDF; ▲ 1.0 mg/mL SDF; ◆ 2.0 mg/mL SDF; mg/mL SDF; ★ 5.0 mg/mL SDF).
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Fig. 4 SEM photographs of of CRS/CT (A), CRS/FG (B), CRS/XG (C), and CRS/KG (D) mixtures. (×1000, Bar=10µm). (0) no SDF; (1) 0.5 mg/mL SDF; (2) 1.0 mg/mL SDF; (3) 2.0 mg/mL SDF; (4) 3.0 mg/mL SDF; (5) 5.0 mg/mL SDF).
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Fig. 5 The X-ray diffraction of CRS/CT (A), CRS/FG (B), CRS/XG (C), and CRS/KG
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(D) mixtures. (no SDF; 0.5 mg/mL SDF; 1.0 mg/mL SDF; 2.0 mg/mL SDF; 3.0 mg/mL SDF; 5.0 mg/mL SDF, from bottom to up ).
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Fig. 1
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Fig. 2
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Fig. 3
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A-1
A-2
A-3
B-0
B-1
B-2
B-3
C-0
C-1
C-2
D-0
D-1
A-4
SC
A-0
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Fig. 4
B-4
B-5
C-3
C-4
C-5
D-3
D-4
D-5
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D-2
5
A-5
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Fig. 5
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Highlights
In the presence of FG, XG and KG, the value of FV increased significantly.
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The 5.0 mg/mL CRS/XG mixtures had strong gel strength. Soluble dietary fibers addition result in higher viscoelasticity of CRS.
The 5.0 mg/mL CRS/KG was the most dense aggregation and had the highest
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relative crystallinity.
S0023-6438(19)30070-2
DOI:
https://doi.org/10.1016/j.lwt.2019.01.059
Reference:
YFSTL 7801
To appear in:
LWT - Food Science and Technology
Received Date: 30 November 2018 Revised Date:
28 January 2019
Accepted Date: 29 January 2019
Please cite this article as: Liu, X., Liu, S., Xi, H., Xu, J., Deng, D., Huang, G., Effects of soluble dietary fiber on the crystallinity, pasting, rheological, and morphological properties of corn resistant starch, LWT - Food Science and Technology (2019), doi: https://doi.org/10.1016/j.lwt.2019.01.059. 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.
ACCEPTED MANUSCRIPT
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Effects of soluble dietary fiber on the crystallinity,
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pasting, rheological, and morphological properties of corn resistant starch
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Xiane Liu, Suchen Liu, Huiting Xi, Junjun Xu, Danwen Deng, Ganhui Huang*,
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State Key Laboratory of Food Science and Technology, Nanchang University,
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Nanchang, 330047, China
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* Corresponding author: Professor Ganhui Huang, PhD, State Key Laboratory of
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Food Science and Technology, Nanchang University, No. 235 Nanjing East Road,
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Nanchang 330047, Jiangxi, China.
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Tel: +86-136 0708 8530;
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E-mail address: (G. Huang) [email protected]
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Abstract In this research, corn resistant starch (CRS) was mixed with four kinds of soluble
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dietary fibers (chitosan, flaxseed gum, xanthan gum, and konjac gum). The pasting and
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rheological properties, microstructure, and X-ray diffraction spectrum of the mixed
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system were investigated by rapid viscosity analyzer (RVA), rheometer, scanning
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electron microscopy (SEM), and X-ray diffractometer (XRD). The pasting curves
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showed that the addition of chitosan could reduce the viscosity of CRS paste, while the
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flaxseed gum, xanthan gum and konjac gum increased the viscosity. All complex
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systems had shear thinning properties in the rheological steady flow experiments.
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Soluble dietary fibers significantly increased the value of viscosity coefficient (K) of the
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CRS, however, the value of flow characteristic index (n) was decreased with increasing
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concentration of soluble dietary fibers. Soluble dietary fibers addition resulted in higher
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storage modulus and loss modulus (G' and G'') of CRS paste, as well as giving rise to
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high viscoelasticity. SEM confirmed that the addition of soluble dietary fibers made the
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starch granules more easily aggregated in the mixed systems. X-ray diffraction spectrum
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analysis showed that the addition of soluble dietary fibers did not change the B and V
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type crystalline pattern of CRS, and both the concentrations and types of soluble dietary
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fibers had significant effects on the crystallinity of mixed systems. This study reported
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four mixtures with CRS and provided useful information for functional food.
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Keywords: resistant starch, soluble dietary fiber, pasting, rheology, morphology
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1. Introduction With the development of food nutriology, resistant starch is widely used in food
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processing as a new type of dietary fiber. On the one hand, resistant starch in food
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industry can increase the content of dietary fiber, overcome some of the deficiencies of
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traditional dietary fiber on the taste, formability and texture of the product, simplify the
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food processing and make food quality better (Marlatt et al., 2017). On the other
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hand, resistant starch containing high dietary fiber is often used to develop new food
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supplements as functional factors, as it can prevent the gastrointestinal diseases and
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cardiovascular disease, reduce postprandial glycemic and insulinemic responses, modify
42
colonic micro-florato form short-chain fatty acids, and promote bacterial growth and
43
mineral absorption (Brouns, Kettlitz, & Arrigoni, 2002; Kendall et al., 2008;
44
Fuentes-Zaragoza, Riquelme-Navarrete, Sánchez-Zapata, & Pérez-Álvarez, 2010).
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Soluble dietary fiber is often used in starch-based product as thickener and
46
emulsifier to control the flow of water and improve the quality and storage performance.
47
Meanwhile, the effects of soluble dietary fiber on starch mainly depend on the sources,
48
species, molecular weight, and compounding ratio of soluble dietary fiber. Extracted
49
from different sources, chitosan, flaxseed gum, xanthan gum and konjac gum have
50
different ionic properties and molecular weights and are commonly used as additives in
51
food processing. Chitosan, exploited from shrimp and crabs, is the only positively
52
charged alkaline cationic linear polysaccharide in nature (Rinaudo, 2007). Josiane et al.,
53
(2016) pointed that the presence of chitosan hindered the formation of starch gel to
54
some extent, and the influences of chitosan on starch were mainly attributed to the
55
competition for water available between biopolymers, thus delaying granule swelling
56
and decreasing the amount of leached amylose for gel formation. Flaxseed gum,
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58
neutral linseed polysaccharide (Ziolkovska, 2012). Wang et al., (2008) reported that the
59
apparent viscosities and the values of G' and G'' of samples increased with flaxseed gum
60
addition increasing, and the flaxseed gum-maize starch mixtures had a gel-like structure.
61
Xanthan gum, obtained from the bacterium Xanthomonas campestris, is a microbial
62
polysaccharide with a primary structure having repeated pentasaccharide units. Xanthan
63
gum is broadly used as a food additive in food industry such as stabilizer and thickener
64
because of its good water solubility, high viscosity, and pseudoplastic rheological
65
properties (Palaniraj, & Jayaraman, 2011; Garcíaochoa, Santos, Casas, & Gómez, 2000).
66
The ddition of xanthan gum in starch was widely reported to control and improve the
67
pasting and rheological properties of starch (Bemiller, 2011; Nawab, Alam, Haq, &
68
Hasnain, 2016; Heyman, Vos, Depypere, Meeren, & Dewettinck, 2014; Heyman, Vos,
69
Meeren, & Dewettinck, 2014). Konjac gum is a non-ionic water-soluble neutral
70
polysaccharide extracted from the underground tuber of herbaceous konjac. It is rich in
71
hydroxyl and carbonyl groups, and has good thickening, emulsification, film formation
72
and stability (Zhang, Chen, & Yang, 2014). Konjac gum was mainly used to
73
synergistically interact with certain gums (Brenner, Wang, Achayuthakan, Nakajima, &
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Nishinari, 2013; Cui, Eskin, Wu, & Ding, 2006; Lin, & Huang, 2003) and replace fat
75
(Dai, Jiang, Corke, & Shah, 2018).
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Previous studies reported that mixtures of starch/soluble dietary fiber were mixed
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with native starch and soluble dietary fiber, while limited information has been covered
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on the mixtures properties of soluble dietary fiber with resistant starch. In this study, the
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effects of four different kinds of soluble dietary fiber on the crystallinity, pasting,
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rheological, and morphological properties of corn resistant starch were investigated by
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and X-ray diffractometer (XRD).
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2. Materials and methods
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2.1. Materials
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The chitosan (CT), flaxseed gum (FG), xanthan gum (XG), and konjac gum (KG)
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were of food grade and obtained from Hebei Baiwei Biotechnology Corporation
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(Handan, China). Corn resistant starch (CRS) (total dietary fiber content: 65.40%;
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resistant starch content: 40.95 ± 1.26%) was acquired from American National Starch
89
Corporation (USA). Glucoamylase (100,000 U/ml), and α-amylase (100,000 U/ml) were
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purchased from Aladdin Reagent Corporation (Shanghai, China). All other chemicals
91
and reagents used in this study were of analytical grade.
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2.2. Determination of resistant starch (RS) content
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The RS content was determined by means of an enzymatic method (AOAC
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2002.02) with a modification. 100 mg CRS (dry basis) was weighed accurately, and
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suspended in distilled water. Then, the suspensions were incubated with α-amylase (500
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U/g) in a water bath at 93 °C and pH 6.5 for 30 min after aging. The non-resistant starch
97
was solubilised and hydrolyzed to glucose by the action of enzyme during the time. The
98
reaction was terminated by mixing it with anhydrous ethanol and the indigested
99
resistant starch was recovered by centrifugation (4800 rpm, 10 min). Then, the
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centrifuged RS was suspended in distilled water. Subsequently, Glucoamylase (5000
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U/g) was added to the above prepared paste, and the paste was incubated in a water bath
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at 60 °C for 30 min after adjusting the pH to 4.5 with a hydrochloric acid solution (1
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activity. The suspensions were centrifuged at 4800 rpm for 15 min by using a centrifuge
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(TGL-15B, Shanghai Anting Scientific Instrument Factory, Shanghai, China). The
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pellet containing the RS was purified with ethanol and solubilized with 2 mol/L KOH.
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The concentration of RS was measured at 510 nm in a spectrophotometer (Shanghai
108
Jingke Industrial Co., Ltd, Shanghai, China). Resistant starch content was calculated as
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the amount of glucose × 0.9. The results were obtained in analytical triplicate and are
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presented as the mean ± the standard deviation.
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2.3. Preparation of suspensions of CRS/SDF
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CRS (60.0 mg/mL) with different concentrations of SDF (0 mg/mL; 0.5 mg/mL;
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1.0 mg/mL; 2.0 mg/mL; 3.0 mg/mL; 5.0 mg/mL) mixtures were prepared as follows.
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Briefly, CT, FG, XG, and KG powder were firstly dissolved in distilled water with
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continuous stirring for 30 min with 150 rpm, respectively. Then the CRS (60.0 mg/mL)
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was dispersed into CT, FG, XG, and KG solutions by magnetic stirring for 10 min with
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150 rpm at room temperature to prepare the mixed suspensions. All suspensions were
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stored for 3 min at room temperature to perform the following determinations.
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2.4. Pasting properties
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Pasting properties of CRS and the mixtures of CRS/CT, CRS/FG, CRS/XG, and
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CRS/KG suspensions were determined by using Rapid Visco Analyzer (RVA, Newport
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Scientific, NSW, Australia). The mixed samples (25 mL) were prepared as described in
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section 2.3. The slurries were poured into aluminium canisters and manually stirred
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using plastic paddles for 20-30 s before insertion into the RVA. The RVA Standard 1
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viscosity (TV), breakdown viscosity (BV), final viscosity (FV), setback viscosity (SV)
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and peak time (PeT) were calculated by RVA system software. And the pasting curve of
128
samples were obtained by means of RVA program. The hot paste of samples were
129
cooled to room temperature, and stored in the refrigerator (5 °C) for 24 h to perform the
130
following determinations.
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2.5. Rheological measurements
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All samples were prepared by RVA (section 2.4) and evaluated using a rheometer
133
(ARES-G2, TA Instruments Inc., USA) with a stainless steel parallel plate (40 mm
134
diameter, 0.5 mm gap). The relationship between the apparent viscosity and shear stress
135
of samples was measured in the shear rate ranging from 1 to 1000 s-1 at 25 °C. The shear
136
stress data was fitted to the power law model expressed by equation (1) (Sun, & Yoo,
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2015; Liu et al., 2018):
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where τ is shear stress (Pa), K is consistency coefficient (Pa·sn), γ is shear rate (s-1), and n is flow behaviour index, R2 is determination coefficient (dimensionless).
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The oscillatory rheological measurements of samples were performed to obtain the
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storage modulus (G'), loss modulus (G''), and loss tangent (tan δ= G″/ G′) at the angular
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frequency sweeps ranging from 0.1 to 126 rad/s in strain 1.0% at 25 °C.
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2.6. Scanning electron microscopy (SEM)
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All samples were obtained as described in section 2.4 and freeze-dried in the
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-80 °C lyophilizer (Labconco Co., USA). The dried samples were finely ground, and
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coated with a thin layer of gold to avoid charging under the electron beam (Garcia-Diaz,
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sample at magnification of 1000× by using SEM (SEM, JSM6701F, Japan) with
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accelerating potential of 5.0 kV.
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2.7. X-ray diffraction (XRD)
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The powder was obtained as described in section 2.6 and measured in an X-ray
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diffractometer (D8 Advance; Bruker Inc., Germany) by using Cu Kα at a speed of
154
10 °/min (Koteswara, Vidya, & Haripriya, 2015). All samples were scanned through the
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diffraction angle of 2θ from 5 ° to 60 ° at a voltage of 40 kV and filament current of 40
156
mA. The area under the crystalline peak curve and the area under the amorphous peak
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were measured with Jade 6.0 software and the relative crystallinity (RC) was estimated
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with Jade 6.0 software according to the following formula (2) :
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AC × 100 % AC + Aα
where AC is the area of the crystalline peak and Aα is the area of the amorphous peak.
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2.8. Statistical analysis
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All measurements were made in triplicate for each sample. All of the graphs were
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plotted by using OriginPro 8.0 software (Stat-Ease Inc., Minneapolis, USA). One-way
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analysis of variance(ANOVA) and the mean separations were analyzed by Tukey’s
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HSD test (p < 0.05) with the SPSS 22.0 Statistical Software Program.
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3. Results and discussion
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3.1. Pasting properties The pasting of starch is the swelling of starch granules at a certain temperature to
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destroy the hydrogen bonds associated with starch granules in the crystallization and the
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amorphous zone (Chen, et al., 2015). The pasting profiles of mixtures of corn resistant
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starch (CRS) and different soluble dietary fiber (SDF) are presented in Fig. 1. The
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pasting parameters of mixtures are shown in Table 1.
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CRS had a low viscosity during pasting due to the fact that high amylose content
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could limit the swelling of starch (Tester & Morrison, 1990). The addition of flaxseed
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gum (FG), xanthan gum (XG), and konjac gum (KG) could increase the apparent
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viscosity of CRS during the pasting process, and the KG had the most significant effect
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on CRS. The increase in viscosity was mainly attributed to the reduction in available
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water molecules for starch granules caused by the competition of water absorption from
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high amount of FG, XG, and KG (Bemiller, 2011). CT could slightly decrease the
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viscosity of CRS. The different behavior between CT and KG was obviously visible.
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This might be due to the fact that CT is the only positively charged alkaline cationic
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polysaccharide in nature, which could limit the swelling of starch granules during the
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pasting. In addition, viscosity increase of CRS resulting from addition of FG, XG, and
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KG were probably due to a higher molar mass (Singh, Gevekeal, & Yadav, 2017). The
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effects of different SDF on the viscosity of CRS were slight at a level of 0.5 - 1.0
187
mg/mL during pasting, however, that of 3.0 - 5.0 mg/mL SDF was significant. It
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indicated that the high concentration of FG, XG, and KG played an important role in
189
starch swelling and could form hydration film by coating around the starch granules to
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it demonstrated that the factors which could affect viscosity of mixtures were complex,
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and the pasting properties were strongly dependent on the type of SDF for given
193
SDF/CRS ratio.
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As shown in Table 1, compared to CRS, the addition of SDF (without CT)
195
significantly (p < 0.05) increased the peak viscosity (PV), trough viscosity (TV),
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breakdown viscosity (BV), final viscosity (FV), and setback viscosity (SV). The
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opposite result has been reported by Qiu, Yadav, Chen, Liu, Tatsumi, & Yin. (2015),
198
which suggested that values of PV and BV of native maize starch decreased with the
199
addition of corn fiber gum (CFG). The value of PV represented the point of maximum
200
granular swelling and reflected water absorption capacity of starch granules, and the
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increase of PV on starch mixtures was often reported in polysaccharides/starch (Kong,
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Zhu, Sui, & Bao, 2015; Bemiller, 2011). The increase in the value of PV might be due
203
to an increased effective molecular size, resulting from physical or chemical interaction
204
between the RS and SDF (Liu, Nam, & Cui, 2003). BV values, calculated with the
205
magnitudes of PV and TV of samples, reflects the stability of starch paste. The addition
206
of KG significantly increased the value of BV of CRS from 4.67 to 244.33 mPa.s,
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suggesting that KG could promote the fragmentation of starch granules during heating
208
process. FV values represent the gel or paste forming capability of starch after cooking
209
and cooling, which were changed between 4.67 and 1000.37 mPa.s at a level of 5.0
210
mg/mL addition. SV represents the differences between TV and FV, and the addition of
211
FG, XG and KG significantly increased SV of CRS (p < 0.05) in the order of KG >
212
FG > XG, which indicated that the addition of FG, XG and KG markedly affected the
213
retrogradation of CRS at the cooling stage (Zhou, Zhang, Chen, & Chen, 2017).
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3.2. Rheological properties
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3.2.1. Steady flow The flow behaviors of mixtures under steady shear conditions at 25 °C are
217
presented in Fig. 2. The consistency coefficient (K), flow behavior index (n), and
218
determination coefficient (R2) for each flow curve were summarized in Table 2. As
219
shown in Fig. 2, the viscosity decreased with the shear rate increasing, illustrating that
220
the internal structure of the mixed systems was destroyed or formed a new structure and
221
all samples exhibited shear thinning behavior under the current experimental conditions
222
(Samutsri, & Suphantharika, 2012). The results in Table 2 demonstrated that the power
223
law model was well fitted to the profile of rheological characteristics of all samples
224
according to the value of R2 ranging from 0.9845 to 0.9999. The values of K of
225
mixtures in the presence of FG, XG, and KG were higher than CRS alone, suggesting
226
that the addition of FG, XG, and KG resulted in more resistance to flow (Kumar,
227
Brennan, Zheng, & Brennan, 2018), which was consistent with the discussion in RVA
228
(Table 1). In this study, the n value of CRS was 1.0435, which indicated that the CRS
229
fluid was similar with Newtonian fluid. And, the SDF significantly (p < 0.05) decreased
230
the value of n of CRS ranging from 0.1620 to 0.9223, suggesting that the mixed systems
231
were the typical pseudoplastic fluid. The CRS/XG at a level of 5.0 mg/mL addition had
232
the lowest n value, which indicated that the 5.0 mg/mL CRS/XG mixture could induce
233
the formation of the strongest gel. Similar results were previously reported by Yuvaret,
234
Piyada, & Manop, (2008), in which they suggested that XG had high shear stability, it
235
could obviously promote re-association of damaged structure induced by high shear rate.
236
The 5.0 mg/mL CRS/KG had the highest K, followed by XG, FG, and CT, respectively.
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3.2.2. Dynamic rheological properties The dynamic viscoelastic properties of sample had considerable significance in the
239
practical application of processing performance and quality control. The loss modulus
240
(G'') represents the viscous behavior of sample and the storage modulus (G') represents
241
elastic behavior of sample. From Fig. 3, it can be seen that the storage modulus (G') of
242
CRS was greater than its loss modulus (G'') during the entire frequency range,
243
indicating that the 60.0 mg/mL CRS paste had a elastic behavior superior to viscous
244
behavior (Chen, Tong, Ren, & Zhu, 2014; Herrera, Vasanthan, & Chen, 2016). It
245
demonstrated that amylose is dominant in swelling of starch and high amylose content
246
could increase the brittleness and strength of starch (Singh, Kaur, & Mccarthy. 2007).
247
The storage modulus (G′) and loss modulus (G″) of mixtures were increased with the
248
increasing of angular frequency (Fig. 3). The addition of SDF obviously increased the
249
dynamic modulus (G′, G″) of CRS, which revealed that the addition of SDF influenced
250
the structure of paste of CRS. In the case of adding CT, XG, and KG, the G′ was
251
obviously higher than G″ and the dynamic modulus (G′, G″) were frequency-dependent.
252
There was’t a crossover between G′ and G″ during the whole frequency range, which
253
suggested that these mixed systems were typical weak gel classified by Clark &
254
Ross-Murphy (1987) in rheology. Similar results were also reported in previous studies
255
on composite system of tapioca starches and xanthan gum (Chaisawang, &
256
Suphantharika, 2006). The addition of 0 - 2.0 mg/mL FG/CRS made mixtures with
257
elastic behavior. However, at the concentration of 3.0 and 5.0 mg/mL FG/CRS, a
258
crossover between the dynamic modulus (G′, G″) was observed in70.5 and 14.1 rad/s,
259
respectively (Fig. 3B).
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3.3. Scanning electron microscopy (SEM) The particle morphology and surface characteristics of all mixtures are shown in
262
Fig. 4. The results obtained by SEM illustrated that the shape of the CRS granules was
263
sphere or oval, the surface was smooth with a slight roughness, and the size ranged from
264
5 to 20 µm in length and from 5 to 10 µm in width. A similar result was observed by
265
Mao, Lu, & Huang, et al. (2018) who studied the morphology of winged yam (Dioscorea
266
alata L.) resistant starch granules. The addition of SDF had no effect on the shape of
267
CRS granules, but the degree of aggregation of CRS granules was significantly affected.
268
The aggregation degree of mixed systems became more pronounced as the amount of
269
SDF increased. When added with different concentration of SDF in CRS, the
270
arrangement of granules was out-of-order. In the case of adding FG, XG, and KG, most
271
of the CRS were tightly wrapped by an adhering gum layer in the continuous phase as
272
shown in Fig. 4. Moreover, the FG, XG, and KG could swell well which resulted in a
273
significant (p < 0.05) increase in PV, TV, BV, FV, and SV during pasting as compared
274
with those obtained form the addition of CT (Table 1). This might be due to the fact that
275
FG, XG, and KG are hydrocolloids which could cross link with leached or gelatinized
276
CRS. It is noteworthy that a protective layer was formed on the surface of CRS and the
277
network structure was enhanced between the CRS and hydrocolloids with the increasing
278
addition of hydrocolloids. The KG/CRS was the most dense aggregation with addition
279
concentration of 5.0 mg/mL, followed by XG, and FG, respectively.
280
3.4. X-ray diffraction (XRD)
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The X-ray diffraction patterns of all samples are presented in Fig. 5. It indicated
282
CRS exhibited strong diffraction peaks at 5.6°, 7.4°, 13.2°, 17.2°, 20.1°, 22.2°, and
13
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284
13.2°~24.0°. The mixed systems exhibited diffraction peaks at 7.4°, 13.2°, 17.2°, 20.1°,
285
22.2°, 23.4°, 25.5°, 23.9°, and 30.5° 2θ compared with CRS. X-ray diffraction patterns
286
of all samples displayed a mixture of B and V-type, although some peaks disappeared
287
and new peaks appeared, which suggested that the cross link of the mixed systems
288
mainly occurred in the amorphous region (Tang, & Copelang, 2007). The intensity and
289
peak width of the diffraction peak were related to the relative crystallinity (RC, %) of
290
the crystallization region. The relative crystallinity (RC, %) of all samples was obtained
291
by formula (2) and shown in Table 3. It illustrated that different concentrations and
292
types of SDF had different effects on the RC (%) of CRS, which indicated that the
293
effects of SDF on CRS were not unique but related to concentrations. The RC (%) of
294
CRS/KG mixtures was the highest at a level of 5.0 mg/mL addition, followed by
295
CRS/XG, CRS/FG, and CRS/CT, respectively. The effects of KG on the crystalline
296
structure of CRS might be due to the reduction of amylose content in the amorphous
297
region and the rearrangement of double helix structure of the amylopectin side chains
298
(Israkarn, Nakornpanom, & Hongsprabhas, 2014).
299
4. Conclusions
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In this study, the effects of soluble dietary fibers on corn resistant starch were
301
evaluated by RVA, rheometer, SEM, and XRD. The viscosity of CRS significantly
302
increased with the increase of amount of FG, XG and KG during the pasting, and konjac
303
gum had the highest viscosity (1000.37 mPa.s), whereas chitosan had the lowest
304
viscosity (1.67 mPa.s). At the addition of 3.0 and 5.0 mg/mL of FG, these mixtures
305
presented a crossover between the dynamic modulus (G′, G″) at angular frequency of
14
ACCEPTED MANUSCRIPT 70.5 and 14.1 rad/s, respectively. Adding soluble dietary fibers into corn resistant starch
307
could improve the pasting, rheological and morphological properties, and konjac gum
308
was the most effective. In general, this study will be useful for formulating desirable
309
pasting, rheological properties, and microstructure, as well as designing and developing
310
new RS-based products at high ratios of soluble dietary fibers.
311
Acknowledgements
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The Graduate Innovative Special Fund Projects of Nanchang University (No.
313
CX2017135) and the First Class Open Fund Projects of Food Science and Engineering
314
of Zhejiang Province (JYTsp20142015) supported this study.
315
Abbreviations
316
CRS, corn resistant starch; SDF, soluble dietary fibers; CT, chitosan; FG, flaxseed gum;
317
XG, xanthan gum; KG, konjac gum; RVA, viscosity analyzer; SEM, scanning electron
318
microscopy; XRD, X-ray diffraction; PV, TV, BV, FV, and SV, peak, trough,
319
breakdown, final, and setback viscosity; PeT, peak time; RC, relative crystallinity; G',
320
storage modulus; G'', loss modulus
321
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Koteswara, R. C., Vidya, P. V., & Haripriya, S. (2015). Effect of chemical modification
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ACCEPTED MANUSCRIPT Table 1
PV (mPa.s)
TV (mPa.s)
BV (mPa.s)
FV (mPa.s)
SV (mPa.s)
PeT (min)
CRS
8.66 ± 0.94ab
3.67 ± 0.47a
4.67 ± 0.47a
5.67 ± 0.47a
2.00 ± 0.00a
1.07 ± 0.00a
0.5 CT
4.33 ± 0.47a
0.00 ± 0.00a
4.33 ± 0.47a
1.67 ± 0.47a
1.67 ± 0.47a
1.11 ± 0.06a
1.0 CT
4.00 ± 0.82a
0.00 ± 0.00a
4.67 ± 0.47a
1.67 ± 0.47a
2.33 ± 0.47a
1.07 ± 0.00a
2.0 CT
5.00 ± 0.00a
0.00 ± 0.00a
4.67 ± 0.47a
2.67 ± 0.47a
2.33 ± 0.47a
1.09 ± 0.03a
3.0 CT
5.33 ± 0.94a
0.67 ± 0.47a
5.00 ± 0.82a
3.33 ± 1.25a
3.00 ± 0.82a
1.13 ± 0.00a
5.0 CT
5.33 ± 0.47a
1.33 ± 0.47a
4.67 ± 0.47a
4.67 ± 0.47a
4.00 ± 0.82a
1.11 ± 0.06a
0.5 FG
9.00 ± 0.82ab
4.67 ± 0.47ab
4.67 ± 0.94a
7.33 ± 0.94ab
3.33 ± 0.47a
1.11 ± 0.06a
1.0 FG
9.67 ± 0.47ab
5.67 ± 0.47abc
4.00 ± 0.00a
9.33 ± 0.47abc
3.67 ± 0.47a
1.07 ± 0.00a
2.0 FG
16.33 ± 0.47ab
10.33 ± 0.47abcd
6.00 ± 0.82a
24.00 ± 0.82cd
13.67 ± 0.94abc
1.18 ± 0.16a
3.0 FG
37.67 ± 0.47e
18.00 ± 0.82d
9.33 ± 0.47ab
44.67 ± 1.25e
26.67 ± 1.25c
1.31 ± 0.21ab
5.0 FG
100.67 ± 2.49g
64.67 ± 5.44gh
18.67 ± 1.25bcd
119.00 ± 6.38g
51.00 ± 5.10d
1.67 ± 0.22bcd
0.5 XG
21.67 ± 1.70bc
20.33 ± 0.47de
2.33 ± 0.47a
21.33 ± 1.70bcd
2.33 ± 0.47a
1.11 ± 0.06a
1.0 XG
35.33 ± 3.86cde
30.67 ± 1.89ef
5.67 ± 0.94a
31.67 ± 1.89de
1.00 ± 0.00a
1.07 ± 0.00a
2.0 XG
68.33 ± 6.18f
57.00 ± 4.32g
13.00 ± 0.82abc
67.67 ± 3.30f
12.33 ± 2.36ab
1.40 ± 0.34abc
3.0 XG
118.67 ± 2.06h
86.33 ± 3.86i
29.00 ± 2.83d
106.33 ± 2.06g
17.33 ± 1.70bc
1.13 ± 0.05a
5.0 XG
221.67 ± 8.38j
199.00 ± 6.98k
26.00 ± 3.74d
221.00 ± 8.83i
25.33 ± 1.25bc
1.29 ± 0.13ab
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Pasting properties of CRS (60.0 mg/mL), CRS/CT, CRS/FG, CRS/XG, and CRS/KG mixtures.
22.67 ± 4.50bcd
16.67 ± 3.40cd
8.33 ± 0.47ab
36.00 ± 4.55de
19.67 ± 1.70bc
1.16 ± 0.06a
37.00 ± 4.55de
16.33 ± 0.94bcd
21.67 ± 3.09cd
69.67 ± 1.25f
53.33 ± 0.47d
1.82 ±0.14cde
57.33 ± 3.40f
35.33 ± 2.06f
22.00 ± 1.41cd
187.67 ± 6.24h
153.00 ± 3.56e
1.89 ± 0.03de
3.0 KG
149.00 ± 9.63i
69.00 ± 5.89h
80.00 ± 5.10e
440.33 ± 6.94j
364.67 ± 13.02f
2.18 ± 0.07e
5.0 KG
363.33 ± 4.99k
152.33 ± 5.91j
244.33 ± 10.66f
1000.67± 8.18k
862.33 ± 4.50g
2.16 ± 0.20e
0.5 KG 1.0 KG 2.0 KG
Values are means ± SD of triplicates. Values in the same column with different superscript are significantly different (p < 0.05).
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Table 2 Steady flow parameters for CRS (60.0 mg/mL), CRS/CT, CRS/FG, CRS/XG, and
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CRS/KG mixtures. R2
K
n
CRS
0.0010a
1.0435u
0.9956
0.5 CT
0.0152g
0.9223o
0.9973
1.0 CT
0.0188h
0.9861t
0.9990
2.0 CT
0.0032b
0.9598s
0.9995
3.0 CT
0.0038c
0.9505r
0.9856
5.0 CT
0.0062e
0.9452q
0.9988
0.5 FG
0.0050d
0.9266p
0.9962
1.0 FG
0.0133f
0.8876n
0.9999
2.0 FG
0.0855k
0.7031l
0.9999
3.0 FG
0.3442m
0.5652k
0.9991
5.0 FG
1.9601p
0.4214i
0.9954
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0.0671j
0.5623j
0.9901
1.0 XG
0.2341l
0.4209h
0.9845
2.0 XG
0.9850o
0.2521f
0.9896
3.0 XG
2.3843q
0.1765c
0.9848
5.0 XG
5.2080s
0.1620a
0.9920
0.5 KG
0.0287i
0.7089m
0.9905
1.0 KG
0.4896n
0.4124g
0.9898
2.0 KG
4.0578r
0.2365e
0.9804
3.0 KG
13.1255t
0.1889d
0.9806
5.0 KG
43.1247u
0.1685b
0.9805
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Values in the same column with different superscript are significantly different (p < 0.05). K is consistence coefficient; n is flow behavior index; R2 is determination coefficient.
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Table 3 The relative crystallinity of CRS (60.0 mg/mL), CRS/CT, CRS/FG, CRS/XG, and
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CRS/KG mixtures. CRS/CT
CRS/FG
CRS/XG
CRS/KG
0
35.98%
35.98%
35.98%
35.98%
0.5
35.81%
34.77%
33.48%
35.06%
1.0
34.85%
37.34%
34.62%
36.33%
2.0
34.33%
37.38%
3.0
31.45%
38.68%
5.0
30.19%
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Concentration
37.54%
38.32%
38.89%
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37.65%
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38.96%
3
38.84%
39.16%
ACCEPTED MANUSCRIPT Figure Captions Fig. 1 Pasting behaviors of CRS/CT (A), CRS/FG (B), CRS/XG (C), and CRS/KG (D) mixtures. (■ no SDF; ● 0.5 mg/mL SDF; ▲ 1.0 mg/mL SDF; ◆ 2.0 mg/mL SDF;
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3.0 mg/mL SDF; ★ 5.0 mg/mL SDF). Fig. 2 Steady flow curves of CRS/CT (A), CRS/FG (B), CRS/XG (C), and CRS/KG (D) mixtures. (■ no SDF; ● 0.5 mg/mL SDF; ▲ 1.0 mg/mL SDF; ◆ 2.0 mg/mL SDF;
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3.0 mg/mL SDF; ★ 5.0 mg/mL SDF).
Fig. 3 Storage modulus (G′) and loss modulus (G″) of CRS/CT (A), CRS/FG (B),
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CRS/XG (C), and CRS/KG (D) mixtures as a function of frequency. The solid symbols represent the storage modulus (G′) and the open symbols represent the loss modulus (G″). (■ no SDF; ● 0.5 mg/mL SDF; ▲ 1.0 mg/mL SDF; ◆ 2.0 mg/mL SDF; mg/mL SDF; ★ 5.0 mg/mL SDF).
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Fig. 4 SEM photographs of of CRS/CT (A), CRS/FG (B), CRS/XG (C), and CRS/KG (D) mixtures. (×1000, Bar=10µm). (0) no SDF; (1) 0.5 mg/mL SDF; (2) 1.0 mg/mL SDF; (3) 2.0 mg/mL SDF; (4) 3.0 mg/mL SDF; (5) 5.0 mg/mL SDF).
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Fig. 5 The X-ray diffraction of CRS/CT (A), CRS/FG (B), CRS/XG (C), and CRS/KG
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(D) mixtures. (no SDF; 0.5 mg/mL SDF; 1.0 mg/mL SDF; 2.0 mg/mL SDF; 3.0 mg/mL SDF; 5.0 mg/mL SDF, from bottom to up ).
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A-1
A-2
A-3
B-0
B-1
B-2
B-3
C-0
C-1
C-2
D-0
D-1
A-4
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B-4
B-5
C-3
C-4
C-5
D-3
D-4
D-5
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Highlights
In the presence of FG, XG and KG, the value of FV increased significantly.
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The 5.0 mg/mL CRS/XG mixtures had strong gel strength. Soluble dietary fibers addition result in higher viscoelasticity of CRS.
The 5.0 mg/mL CRS/KG was the most dense aggregation and had the highest
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relative crystallinity.