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Effect of guar gum on stability and physical properties of orange juice
Accepted Manuscript Title: Effect of guar gum on stability and physical properties of orange juice Authors: Ruihuan Lv, Qing Kong, Haijin Mou, Xiaodan Fu PII: DOI: Reference:
S0141-8130(16)32471-0 http://dx.doi.org/doi:10.1016/j.ijbiomac.2017.02.031 BIOMAC 7086
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
16-11-2016 26-1-2017 8-2-2017
Please cite this article as: Ruihuan Lv, Qing Kong, Haijin Mou, Xiaodan Fu, Effect of guar gum on stability and physical properties of orange juice, International Journal of Biological Macromolecules http://dx.doi.org/10.1016/j.ijbiomac.2017.02.031 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.
Effect of guar gum on stability and physical properties of orange juice
Ruihuan Lv, Qing Kong*, Haijin Mou, Xiaodan Fu College of Food Science and Engineering, Ocean University of China, Qingdao, China *Corresponding author TEL: +86-532-8203-1851; FAX: +86-532-8203-2272; EMAIL: [email protected]
Highlights ·The influence of guar gum on orange juice was investigated. ·The optimal formulation in orange juice was 0.1% guar gum (584 mpa·s) combined with 0.03% CMC. ·Guar gum can significantly reduce the concentration of CMC in fruit juice.
Abstract The objective of current study was to determine the stability and physical properties of orange juice which was added with guar gum. The optimal formulation showed good stability and physical properties, in light of better indices on the serum
cloudiness (turbidity), sensory analysis, particle size distribution, aroma concentration analysis and rheological properties. By serum cloudiness (turbidity), the viscosity of optimal guar gum used in orange juice was 584 mpa·s; by the other four methods, the optimal formulation was determined: 0.1% guar gum (584 mpa·s) combined with 0.03% carboxymethyl cellulose (CMC). The results indicated that the guar gum can be used to partially replaced CMC and improve the stability and physical properties of orange juice.
Keywords Guar gum; orange juice; stability; physical properties
1. Introduction Colloids are a kind of important food additives, which are closely related to food quality and sensory quality. They function as foaming agents, edible coatings, thickeners, stabilizers, etc. The main reason for the wide use of colloids in the food
industry is their ability to absorb water and change the properties of food ingredients [1]. However, a large portion of the colloids used in the food industry is chemically synthesized, which poses potential hazards on public health. Guar is planted mainly in the semi-arid regions of South Asia with a large yield. Guar gum (GG), a natural polysaccharide, is obtained from the seed endosperm of the plant Cyamopsis tetragonolobus. It is a galactomannan, which consists of linear backbone chain of β-1,4-linked mannose units with α-1,6-linked galactose units (2:1) as a side chain [2]. Its unique chemical structure determines the GG has the ability of strong water absorption, a wide range of viscosity stability and good water solubility and crosslinking. Therefore, guar gum has wide applications in food products as a thickener, such as ice cream, sauces, instant foods, syrups, etc. GG can also be used as a soluble dietary fiber in food products, and the allowable daily intake (ADI) is 20 g [3,4]. Due to its high viscosity, the application of GG in food industry is limited, and physical properties of GG can be improved by the controlled partial enzymatic hydrolysis using acidic β-D-mannase, which hydrolyzes GG by selectively cutting mannose backbone chain, decreasing the molecular weight of GG significantly [3]. When dispersed in water, partial hydrolyzed guar gum (PHGG) with lower molecular weight gives low viscosity solution compared with its native chemical. Recently, GG, as a good source of water-soluble dietary fiber, has been studied extensively for its health benefits, like increase in defecating frequency and reduction in serum cholesterol, glucose concentration and free fatty acid [5,6], and it also can reduce glycemic response, inflammation and inflammatory bowel diseases [7,8]. Furthermore,
GG also can improve barrier properties and mechanical strength of nano-composites as biodegradable packaging film [9,10]. Orange, containing abundant organic chemicals and vitamin C, is one of the most productive fruits in the world, and orange juice is among the most popular and desirable products in the world. In order to maintain or increase the consistency and extend the shelf life of orange juice, carboxymethyl cellulose (CMC) is commonly used in fruit juice and other food industries due to its electrostatic repulsion between the CMC molecules so as to improve the stability [11]. However, most countries around the world have set up strict limits on chemically synthesized CMC. To the best of our knowledge, few studies related to the usage of GG in fruit juice are reported. The purpose of our study was to replace the partial amount of CMC by GG in fruit juice. In this context, the effect of GG on the physical stability, serum cloudiness (turbidity), sensory analysis, particle size distribution (PSD), aroma concentration and rheological properties of the orange juice were also evaluated.
2. Materials and methods 2.1 Materials GG used in this study was obtained from Romer Ltd. (Qingzhou, Shandong, China). Acidic β-D-mannase was obtained from Beijing micro-science Biotech Corp (Beijing, China). Xanthan gum, CMC and agar were obtained from Sangon Biotech Ltd (Shanghai, China). The oranges (Citrus sinensis) were purchased from Liqun Company of Qingdao and stored at the temperature of +7
and 80-90% humidity for
a maximum of 48 h before processing. 2.2 Enzymatic hydrolysis of GG GG was subjected to enzymatic hydrolysis using the acidic β-D-mannase (50,000 U) at 0.2 g/L. Firstly, distilled water was adjusted to pH 3 by adding citric acid [12]. After adding 20 g/L of GG powder into the solution, the solution was mixed under continuous magnetic stirring for 24 h at room temperature (25-28 ). After that, acidic β-D-mannase was added into the solution. During hydrolysis, GG solution was placed in a thermostatic water bath at 45
for 5, 25 and 40 min. And then the GG solution
was put into a thermostatic water bath at 80
for 20 min to terminate the enzymatic
reaction. Finally, a low viscous hydrolyzed GG solution was obtained and then lyophilized to get pure PHGG powder. 2.3 Determination of intrinsic viscosity and molecular weight The intrinsic viscosity was estimated using rheometer (AR2000ex, TA Instruments, USA) at 25
in a concentration of 2% for GG and PHGG. Before using
the rheometer, all of the solutions were prepared by dispersing GG powder and PHGG powder in a vortex of water under mild magnetic stirring for 30 min. After that, the solutions were placed for complete hydration for 12h at room temperature to reach maximum viscosity. When estimated the intrinsic viscosity, shear rate was set at 300s-1. The HPGPC-MALLS method was used to determine the molecular weight of GG and PHGG with different viscosity [13]. Three mg/ml aqueous solution of the samples were prepared, then filtered through 0.22 µm microporous membrane. The
determination of molecular weight was carried out using the Agilent Technologies 1260 HPLC (Agilent, Santa Clara, CA, USA). The flow rate was 0.6 ml/min, the injection volume was 100 µl, the mobile phase was sodium sulfate solution (0.1M), and the column temperature was set at 35 . The column consisted of two columns in tandem: HQSB 804 and HQSB 802.5 (Showa Denko Corporation, Tokyo, Japan). And the detector was DAWN HELEOS
eighteen angle laser instrument (Wyatt, Santa
Barbara, CA, USA). The standard curves of viscosity and molecular weight was made. 2.4 Preparation of orange juice samples Firstly, the oranges were washed and sliced. Secondly, the prepared oranges were divided into several parts and put into the electric juicer. Next, the orange juice was filtered through four layers of gauze to separate pulp suspensions and tissue components. Finally, the orange juice was poured into the 250 ml conical flask. 2.5 Effect of GG and PHGG on the stability of orange juice 2.5.1 Single factor The orange juice samples (150 ml) were placed in 250 ml conical flasks, respectively. 0.1%, 0.3%, and 0.5% of GG (584 mpa·s) and PHGG (3.3 mpa·s, 54 mpa·s, 151.4 mpa·s) were added to the samples, respectively. After homogenization for 1 min, the samples were put in refrigerators (4 ) for 24 h. The stability of orange juice was assessed by serum cloudiness (turbidity). Forty ml of the stored juice were added into 50 ml centrifuge tubes, and then centrifuged at 4000 r/min for 15min at 25
(Zhao Di Biological Technology, Shanghai, China). The
supernatant was diluted by 1 time and then measured by the UV-visible spectrophotometer (Shanghai Precision Scientific Instrument, Shanghai, China) calibrated with distilled water. The absorbance at 660 nm was directly related to the turbidity of orange juice [14]. 2.5.2 Effect of GG and other colloids on the stability of orange juice The orange juice samples (150 ml) were placed in conical flasks. GG (584 mpa·s) was combined with CMC (0.03%, 0.05%), agar (0.1%, 0.15%, 0.2%) and xanthan gum (0.03%, 0.06%), respectively. Then the mixture of colloids was added into the orange juice, homogenized for 1min, and put in refrigerators (4 ) for 24 h. The stability of orange juice was also assessed by the serum cloudiness (turbidity). 2.6 Effect of GG on physical properties and stability of orange juice 2.6.1 Sensory analysis Orange juice was prepared at room temperature with four different formulations and the other one was a control group with no colloid. The five orange juice samples were evaluated by a trained descriptive panel. This panel was composed of nine highly trained people (four males and five females, within the age of 20-30 years), each of them had more than 100 h of experience in evaluation of orange juice. The panelists were trained on flavor attributes before the actual evaluation. The different coded samples were tasted by each assessor. The acceptance testing of attributes (appearance, flavor, aroma, texture, overall impression) using a 20-point hedonic scale (1 means disliked very much and 20 means liked very much) was performed on the orange juice. Orange juice was evaluated in duplicate by every assessor. Drinking
water at room temperature to clean mouth before and between evaluations of the orange juice. Finally, the average score and total score were calculated. 2.6.2 Particle size distribution (PSD) The PSD of orange juice was determined by the Laser Particle Size Distribution Analyzer (Malvern Zetasizer, England). The aforementioned four formulations and the control group were diluted by taking one ml into nine ml water, after thoroughly mixing the samples were put into the Analyzer to measure the PSD. In addition to the particle size distribution, the volume-based mean diameter (D[4,3] Eq. (1)) was evaluated [14]. Through its particle size distribution and the volume-based mean diameter (D[4,3]), the stability of orange juice can be judged. D[4,3]= ΣniDi4/ΣniDi3
(1)
Where ni is the percentage of particles with a diameter Di. 2.6.3 Aroma analysis by Gas chromatography-mass spectrometry (GC-MS) A carboxen/polydimethylsiloxane fiber (100 µm PDMS Supelco, Bellefonte, USA) was selected for aroma analysis, as suggested in previous studies [15]. The solid-phase micro extraction (SPME) fiber was conditioned in the injector of an Agilent Technologies 6890N/5973i network (GC-MS) system (Agilent, Santa Clara, USA) at 250
for 1 h before starting extraction [16]. Five ml of the respective
aforementioned four samples was transferred into the 20 ml headspace vial, 1.8 g NaCl was added to facilitate the volatile components in the volatile sample, and internal standard (2 µl cyclohexanone) was also added to each vial before SPME analysis. The silicone PTFE septa was used to sealed the vials containing the mixtures
and held the vials on a magnetic stirrer at 40
for 15 min, after that the activated
SPME extraction head was inserted into the vial bottle, headspace absorbed for 40 min. After that, the fiber was then inserted into the injection port at a depth of 4 cm for the complete desorption, each test was run three times in parallel. The aroma analysis was carried out by a HP-5MS column (30 m×0.25 mm, 0.25 µm; Agilent, Santa Clara, CA, USA). The initial temperature of the GC oven was set
at 50
for 2 min, and was then increased at a speed of 5 /min until it reached 250 ,
where it was held for 5 min. The carrier gas was high-purity helium, and a flow rate was set at 1 ml/min under the constant flow mode. The injection port was heated at 250
under the splitless injection mode. The mass spectrometer was progressed
positive electron impact ionization mode (EI+, 70ev) and the mass scan range from 40 m/z to 450 m/z. The cyclohexanone was used as internal standard for quantitative analysis, to assume the response frequency of each aroma was the same as the internal standard, the amount of each substance was calculated by Eq. (2). M= (A1×M0)/ (A0×V)
(2)
Where M is the content of substance to be measured (µg/ml), A0 is the quality of the internal standard (µg), A1 is the peak area of the material to be measured, M0 is the peak area of the internal standard (µg), and V is the volume of sample (ml). 2.6.4 Rheological characteristic analysis of orange juice As the fruit juice are composed by an insoluble phase dispersed in a viscous solution, the rheological was carried out on orange juice. The rheological characteristic analysis of orange juice was carried out using the rheometer (AR2000ex,
TA Instruments, USA). The temperature of measured was maintained constantly at 25
using a Peltier system, and each sample was analyzed three times. The orange
juice samples were firstly placed in the rheometer and maintained for 1 min before shearing. After that, the shear stress and intrinsic viscosity were recorded with the shear rate changed from 0.1 s-1 to 100 s-1, the flow curve for orange juice with five different formulations was made and analyzed. 2.7 Statistical analysis All data analysis, including serum cloudiness, the score of sensory analysis, particle size distribution, aroma concentration and the rheological characteristics, were presented as the mean ± standard deviations (SD). Paired t-tests and linear regression were performed using IBM SPSS Statistics version 19.0. P≤0.05 was the level of significance. And each experiment was repeated at least three times.
3. Results and discussion 3.1 The determination of intrinsic viscosity and molecular weight By measuring the intrinsic viscosity and molecular weight of GG, the relationship between intrinsic viscosity and molecular weight was calculated. The intrinsic viscosity of GG exhibited a linear relationship with molecular weight of GG, and its linear equation was y=4.3145x+77.168 (R2=0.9978, where x was intrinsic viscosity (mpa·s), y was molecular weight (kDa)) (Fig. 1.). According to this equation, the intrinsic viscosity 3.3 mpa·s, 51.4 mpa·s, 154 mpa·s and 584 mpa·s were corresponded to 71 kDa, 275 kDa, 816 kDa and 2,580 kDa, respectively. 3.2 Single factor of GG and PHGG
To judge whether the orange juice was in a steady state, the serum cloudiness (turbidity) was used as the evaluation index. The greater the serum cloudiness, the better stability of the orange juice. Generally speaking, when the serum cloudiness at the range of 0.95~1.35, the stability of orange juice is commonly accepted. Table 1 showed the serum cloudiness (turbidity) of different concentration and viscosity of GG and PHGG, where significant variations of serum cloudiness in relation to the concentration and viscosity were observed (p<0.01). The serum cloudiness of the sample with a concentration of 0.1% and viscosity of 3.3 mpa·s was the lowest, the GG with a concentration of 0.5% and viscosity of 584 mpa·s was the biggest; furthermore, the turbidity increased with the increasing of GG concentration and viscosity. The stability of orange juice is reflected by the value of turbidity. Before the evaluation, the orange juice samples were centrifuged at first, and only the supernatant was put into the spectrophotometer to evaluate its absorbance [14]. The absorbance is only associated with the orange juice sample turbidity, being the suspended particles responsible for the absorption of radiation. According to the Stokes Law (Eq. (3)), the larger size particles are easier to precipitate, and the smaller size particles tend to remain in the supernatant after centrifugation. A good thickener can prevent the formation of large polymers. The different absorbance values were mainly influenced by the particles that remained in suspension, as observed in Table 1. In Table 1, it was obviously that GG with viscosity of 584 mpa·s was the best, and the greater the concentration of GG, the greater the serum cloudiness. So, the GG with the
viscosity of 584 mpa·s was chosen to be assessed in the next steps. V0= (dp2 (Ps-Pf) g)/18Vf
(3)
Where V0 is Settling velocity of particles (cm/s); dp is Diameter of particles (cm); Ps is Density of particles (g/cm3); Pf is Fluid density (g/cm3); Vf is Fluid viscosity (Pa); and g is Acceleration of gravity (9.8m/s2). 3.3 Effects of mixtures of GG and several colloids The effect of mixtures of GG and several colloids on orange juice was also evaluated by turbidity. It was obviously that the turbidity of 0.5% GG mixed with other colloid was the biggest of all the formulations (p<0.01), and 0.1% GG mixed with other colloid was the lowest (p<0.01) (Fig. 2). The turbidity was correlated with the concentration of GG. From Fig. 2, the serum cloudiness (turbidity) of orange juice with 0.5% GG was the biggest. However, the orange juice with 0.5% GG would make the juice sticky and affect the taste, so the 0.5% GG was abandoned. On the other hand, the serum cloudiness of orange juice with 0.12% CMC was 1.276, and 0.12% CMC was the amount that added in most of factories, so it was taken as the standard. The low turbidity reflected the characteristics of the orange juice that were unstable, but the high turbidity reflected orange juice were too sticky. Taking into account their stability and cost, four formulations were chosen at last, they were: (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum. All of the following experiments were carried out with the 4 formulations and a
control group which was only orange juice. 3.3 Sensory analysis The acceptance of orange juice formulations was shown in Table 2. The score of 0.1% GG combined with 0.03% CMC was the highest, and its effect was significantly better than the other formulations (p<0.01), indicating the orange juice which was added with 0.1% GG combined with 0.03% CMC was better than orange juice with no colloid, in terms of their appearance, flavor, or texture. In contrast, the presence of 0.3% GG combined with 0.03% xanthan gum was the worst, maybe because orange juice that added this formulation was too sticky and a large amount of bubbles existed on the juice liquid surface, these would affected people’s taste. Acceptance of the products with colloid is important because consumers aren’t interested in consuming orange juice which is stratification and has a large amount of bubbles. Acceptance scores for appearance was between 14 and 19 on a hedonic scale of 20 points, indicating that consumers liked the products. Since aroma of juice is the most important factor that affect the orange juice, all consumers like orange juice with good flavor and aroma. In terms of the texture, it is also an important factor, generally soft texture is easy to accept by human. However, the formulation of (C) and (D) made the orange juice sticky, therefore, the colloid that added to orange juice should keep the original taste of juice. It was obviously that (A), 0.1% GG combined with 0.03% CMC, was the best formulation, people liked this even than the orange juice with no colloid. Therefore, based on the sensory analysis, the best formulation was 0.1% GG combined with 0.03% CMC.
3.4 Particle size distribution Fig. 3 showed the particle size distribution (PSD) of the orange juice with five different formulations. It could be seen that the PSD of the samples (A), (B), (D) were similar, all of them had two peaks, and they were different from samples (C) and (E) which only had one peak. Fig. 4 showed the mean particle diameter based on the volume (D[4,3]) for the evaluated samples. It was noteworthy that the mean particle diameter of orange juice with colloid was higher than the orange juice with no colloid (p<0.01). And the mean particle diameter of orange juice with GG and xanthan gum were higher than the others (p<0.01). It is well-known that the main reason for fruit juice precipitation is the existence of some insoluble material such as pulp, because of the difference between the density of insoluble material and fruit juice, these substances are easier to precipitate under the influence of gravity. According to the Stokes Law (Eq. (3)), the downward gravity of each particle should be equal to the sum of the buoyancy force and the frictional resistance of the medium. The Eq. (3) is suitable for the particle diameter bigger than 2 µm, and the pulp is in line with the conditions of the formula particles. From this formula, settling velocity is related to particle diameter, particle density, medium viscosity and medium density. The main way to improve the stability of orange juice are to adjust the particle radium and increase the viscosity of liquid. From Fig. 3, it could be seen that (A), (B) and (D) had two peaks, one of the peak height was 1080 nm, the other was 4300 nm, and there was no overlap between the two peaks. However in terms of
samples (C) and (E), it only had one peak which peak height was 3600 nm. The differences between samples’ peak maybe due to the components of samples with good stability could distribute evenly and didn’t produce any precipitation, so each peak could represent the individual components of the sample. In contrast, the components of samples with bad stability could aggregate together and form a macromolecular polymer, so there was only one peak that represented the polymer peak. On the other hand, according to Eq. (3), the smaller particle size of the juice, the more stable it is. Although the mean particle diameter based on the volume (D[4,3]) of samples which added the GG were higher than the samples that added no colloid, the stability of them was also better than the samples that added no colloid. In conclusion, by adjusting the mean particle diameter and increasing the viscosity of liquid, 0.1% GG combined with 0.03% CMC (A) and 0.3% GG combined with 0.1% agar (B) would provide better formulations. 3.5 Aroma analysis in the 5 orange juice samples The SPME-GC-MS technology was used to detect the difference of aroma components in orange juice which added different formulations. Table 3 showed the content of main ion chromatograms of aroma compounds in the orange juice. A total of 31 aroma compounds were identified in the headspace of orange juice (Table S1). The most abundant aroma compound was 2-methyl-cyclopentanone, up to 50%. Analysis of the volatile composition of orange juice showed that ketones and alkenes were the most representative compounds aroma in all chromatographic profiles for all of the five different formulations, accounting for more than 90% of the total volatile
fraction. Previously, Tietel et al had reported that limonene, linalool, α-pinene, decanal and butanoic acid ethyl ester were the important aroma compounds [17]. Terpene is an important group of aroma compounds in orange juice, including limonene, α-pinene, α-panasinsen and caryophyllene. There is a large amount of limonene in orange juice which belongs to single terpenoids with a light lemon flavor and active chemical property. In this study, the content of limonene in the formulations of (A), (B), (C) and (D) were all lower than (E) (p<0.01), indicating that GG maybe inhibit the volatilizations of limonene. In considering to the α-pinene, its content in the formulation (A) was higher than that in the other 4 formulations (p<0.01), but the content of α-pinene in other 4 formulations were the same basically, indicating that GG maybe had no effect on the volatilizations of α-pinene. And in terms of α-panasinsen, the formulations of (A), (B) and (D) were higher than (E) (p<0.01), indicating that GG maybe promoted the volatilizations of it. And as for the caryophyllene was concerned, the content of it in formulations (A), (B), (C) and (D) were all higher than (E) (p<0.01), indicating that GG maybe also promoted the volatilizations of caryophyllene. Linalool is the main alcohol in orange juice with a mellow fragrance of flowers, it has an important contribution to the abundant aroma of orange juice. And its chemical property is active, it can produce α-terpineol by a series of reaction under certain conditions. The content of linalool in the formulations that was added with colloid was all higher than that in the control group (p<0.01), indicating that GG
maybe had a good effect on its release. Decanal is the characteristic aroma component of orange juice with a typical fruity, but it was only detected in formulation (A). And butanoic acid ethyl ester is a common aroma in orange juice, it is the most important ester aroma too. However, the content of butanoic acid ethyl ester in the formulations (A), (B), (C) and (D) were lower than the control group, but the difference of it was not obvious, indicating that GG maybe had a slight inhibitory effect on its release. Among the total aroma compounds isolated (31), 13 of them had no significant differences compared with the control group. The rest of compounds (18) were significantly influenced by GG, including limonene, linalool, α-pinene, decanal and butanoic acid ethyl ester. In general, most of the aroma compounds were presented at a low concentration. This showed the GG have an effect on the release of aroma compounds. Considering the differences aroma compounds between these formulations, it was obviously that the aroma compounds of formulation (A) was better than the others both on the characteristic aroma and other aroma compounds. 3.6 Rheological characteristic analysis of orange juice Rheological behavior of five different formulations orange juice was analyzed at 25 . The curve of shear stress-shear rate was shown in Fig. 5 and the curve of viscosity-shear rate was shown in Fig. 6, the 5 curves in those figures represented the 5 different formulations, respectively. All of the orange juices showed pseudo plastic behavior, indicating that added colloids to the orange juice won’t change the rheological properties of it. In Fig. 5, the rheological properties of different thickening agents could be clearly observed, the shear stress was also increasing with the
increase of the shear rate, but the ratio of shear stress and shear rate was decreasing with the increase of shear rate. Therefore, the orange juice that added thickening agent was a typical shear thinning system, and the juice with no colloid didn’t change significantly. The change of viscosity in different shear rate of orange juice with different thickening agents was shown in Fig. 6. In contrast to the shear stress, with the increase of shear rate, the viscosity of the orange juice became smaller. The viscosity of the orange juice that added 0.3% GG combined with 0.03% xanthan gum was the largest at the same shear rate, and the viscosity of the orange juice that added 0.1% GG combined with 0.03% CMC was the smallest. However, the viscosity of the control group had no change, and it belonged to newton fluid. Considering the effects of different thickening agents on several main aroma substances in orange juice, there was no direct relationship between the viscosity and the aroma released from the orange juice, which was the same with the other studies. Bylaite et al had reported that the acting force of the aroma compounds and the xanthan gum was determined by the physical and chemical properties of the aroma substance, but not with the viscosity of the solution, and added the thickener even promoted the volatilize of aroma substance [17,19]. In the same way, Siefarth et al also pointed out that the relationship between solution viscosity and aroma release was not significant in low viscosity solutions [20].
4. Conclusions The present work evaluated the effect of GG and its combination with other
colloids on the stability and physical properties of orange juice. Based on the results from serum cloudiness, sensory analysis, particle size distribution, aroma analysis and rheological characteristics analysis, it was concluded that 0.1% GG combined with 0.03% CMC will form the best formulation. It can be concluded that the GG may have the potential to be utilized as a thickening agents that added to the orange juice. So when it is added to the fruit juice, it can prevent the fruit juice from stratification and precipitation, and it also makes the product have a good creamy taste. On the other hand, the GG can successfully be used as a source of soluble dietary fiber due to its functional properties [12]. Therefore, the GG can be widely used in orange juice as it will not affect the quality of orange juice, and it can significantly reduce the concentration of CMC.
Acknowledgment This research was supported by the National Natural Science Foundation of China (31471657).
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Figure Captions: Fig. 1. The relationship between intrinsic viscosity and molecular weight distribution. Error range of all values were between ±5%- 20%. Vertical bars represent the standard deviation. Fig. 2. The serum cloudiness of different concentration GG with other colloid on orange juice. (A) 0.1% 584mpa·s GG; (B) 0.3% 584mpa·s GG; (C) 0.5% 584mpa·s GG. Vertical bars represent the standard deviation. Fig. 3. Particle Size Distribution of the orange juice with 5 different formulations. (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group. Fig. 4. Mean particle diameter for volume-based mean diameter (D[4,3]). Vertical bars represent the standard deviation. (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group. Fig. 5. Effect of shear rate on shear stress of orange juice with 5 different formulations. (█) 0.1% GG combined with 0.03% CMC; (●) 0.3% GG combined
with 0.1% agar; (▲) 0.3% GG combined with 0.03% xanthan gum; (★) 0.1% GG combined with 0.06% xanthan gum; (◆) control group. Fig. 6. Effect of shear rate on viscosity of orange juice with 5 different formulations. (█) 0.1% GG combined with 0.03% CMC; (●) 0.3% GG combined with 0.1% agar; (▲) 0.3% GG combined with 0.03% xanthan gum; (★) 0.1% GG combined with 0.06% xanthan gum; (◆) control group.
Fig. 1. The relationship between intrinsic viscosity and molecular weight distribution. Error range of all values were between ±5-20%. Vertical bars represent the standard deviation.
c
a
b e
d
f
e
d
e
c
a
f
b
f
a
d
d
c g
e
b
Fig. 2. The serum cloudiness of different concentration GG with other colloid on orange juice. (A) 0.1% 584mpa·s GG; (B) 0.3% 584mpa·s GG; (C) 0.5% 584mpa·s GG. Vertical bars represent the standard deviation.
Size Distribution by Volume
(A)
Volume (Percent)
20 15 10 5 0 0.1
1
10
100
1000
10000
Size (d.nm)
Record 1: 1 1
Size Distribution by Volume
(B)
Volume (Percent)
15
10
5
0 0.1
1
10
100
1000
10000
Size (d.nm)
Record 3: 2 2
Size Distribution by Volume
(C)
Volume (Percent)
30
20
10
0 0.1
1
10
100 Size (d.nm)
Record 7: 3 3
1000
10000
Size Distribution by Volume
(D)
Volume (Percent)
20 15 10 5 0 0.1
1
10
100
1000
10000
Size (d.nm)
Record 10: 4 3
Size Distribution by Volume
(E)
Volume (Percent)
20 15 10 5 0 0.1
1
10
100
1000
10000
Size (d.nm)
Record 14: 6 1
Fig. 3. Particle Size Distribution of the orange juice with 5 different formulations. Formulation: (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group.
b c
a
d e
Fig. 4. Mean particle diameter for volume-based mean diameter (D[4,3]). Vertical bars represent the standard deviation. (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group.
Fig. 5. Effect of shear rate on shear stress of orange juice with 5 different formulations. (█) 0.1% GG combined with 0.03% CMC; (●) 0.3% GG combined with 0.1% agar; (▲) 0.3% GG combined with 0.03% xanthan gum; (★) 0.1% GG combined with 0.06% xanthan gum; (◆) control group.
Fig. 6. Effect of shear rate on viscosity of orange juice with 5 different formulations. (█) 0.1% GG combined with 0.03% CMC; (●) 0.3% GG combined with 0.1% agar; (▲) 0.3% GG combined with 0.03% xanthan gum; (★) 0.1% GG combined with 0.06% xanthan gum; (◆) control group.
Table 1 The turbidity of different composition guar gum on the orange juice. Concentration Viscosity 0.1%
0.3%
0.5%
3.3 mpa·s
0.518±0.04Cd
0.631±0.02Bd
0.689±0.06Ad
51.4 mpa·s
0.713±0.05Cc
0.721±0.04Bc
0.750±0.03Ac
154 mpa·s
0.835±0.03Cb
0.865±0.07Bb
0.970±0.06Ab
584 mpa·s
1.042±0.03Ca
1.072±0.06Ba
1.429±0.05Aa
Data were shown as means ± standard deviation followed by different upper case and lower case letters indicate significant differences at p ≤ 0.05 between different rows and columns, respectively.
Table 2 Acceptance of the orange juice formulations.
Formulation Parameter (A)
(B)
(C)
(D)
(E)
Appearance
18.4±0.5a
17.2±0.4b
14.4±0.7c
14.4±0.3c
14.7±0.5c
Flavor
18.9±0.6a
17.2±0.3b
16.1±0.6c
14.8±0.5d
17.8±0.2b
Aroma
12±0.3b
10.1±0.5c
8.9±0.2d
10.3±0.3c
13.8±0.3a
Texture
13.9±0.8a
13.4±0.6a
10±0.3d
11.8±0.4c
13.1±0.7b
Overall impression
12.8±0.4a
10.6±0.4c
10.1±0.7c
11.2±0.6b
12.2±0.5a
Total score
76±0.3a
68.5±0.3c
59.5±0.8e
62.5±0.5d
71.6±0.7b
Hedonic values (appearance, flavor, aroma, texture and overall impression): 1-disliked very much; 20-liked very much. Formulation: (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group Data were shown as means ± standard deviation followed by different lower case letters indicate significant differences at p ≤ 0.05 between different columns.
Table 3 The main aroma compounds of orange juice formulations. Aroma
Formulation
compound
(A)
(B)
(C)
(D)
(E)
Butanoic acid, 2.19±0.16b
2.18±0.04b
2.26±0.03a
2.02±0.08c
2.29±0.05a
68.21±0.29a
41.58±0.12c
49.87±0.11b
35.11±0.05e
38.01±0.08d
0.36±0.07a
0.22±0.03b
0.24±0.04b
0.26±0.03b
0.23±0.03b
0.74±0.16a
0.48±0.05d
0.55±0.03c
0.47±0.04d
0.62±0.02b
45.24±0.39b
35.29±0.07d
34.87±0.06e
36.81±0.04c
53.19±0.05a
0.28±0.03a
0.21±0.02b
0.22±0.01b
0.21±0.03b
0.16±0.01c
Decanal
0.21±0.02
N/D
N/D
N/D
N/D
Caryophyllene
0.16±0.02b
0.13±0.01b
0.15±0.02b
0.21±0.03a
0.07±0.01c
Linalool
0.71±0.07a
0.44±0.07b
0.49±0.05b
0.41±0.08bc
0.35±0.03d
α-panasinsen
0.30±0.04b
0.27±0.02b
N/D
0.39±0.03a
0.19±0.02c
ethyl ester 2-methyl-cyclop entanone α-pinene Hexanoic acid,ethyl ester Limonene Octanoic acid, ethyl ester
Formulation: (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group Data were shown as means ± standard deviation followed by different lower case letters indicate significant differences at p ≤ 0.05 between different columns.
S0141-8130(16)32471-0 http://dx.doi.org/doi:10.1016/j.ijbiomac.2017.02.031 BIOMAC 7086
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
16-11-2016 26-1-2017 8-2-2017
Please cite this article as: Ruihuan Lv, Qing Kong, Haijin Mou, Xiaodan Fu, Effect of guar gum on stability and physical properties of orange juice, International Journal of Biological Macromolecules http://dx.doi.org/10.1016/j.ijbiomac.2017.02.031 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.
Effect of guar gum on stability and physical properties of orange juice
Ruihuan Lv, Qing Kong*, Haijin Mou, Xiaodan Fu College of Food Science and Engineering, Ocean University of China, Qingdao, China *Corresponding author TEL: +86-532-8203-1851; FAX: +86-532-8203-2272; EMAIL: [email protected]
Highlights ·The influence of guar gum on orange juice was investigated. ·The optimal formulation in orange juice was 0.1% guar gum (584 mpa·s) combined with 0.03% CMC. ·Guar gum can significantly reduce the concentration of CMC in fruit juice.
Abstract The objective of current study was to determine the stability and physical properties of orange juice which was added with guar gum. The optimal formulation showed good stability and physical properties, in light of better indices on the serum
cloudiness (turbidity), sensory analysis, particle size distribution, aroma concentration analysis and rheological properties. By serum cloudiness (turbidity), the viscosity of optimal guar gum used in orange juice was 584 mpa·s; by the other four methods, the optimal formulation was determined: 0.1% guar gum (584 mpa·s) combined with 0.03% carboxymethyl cellulose (CMC). The results indicated that the guar gum can be used to partially replaced CMC and improve the stability and physical properties of orange juice.
Keywords Guar gum; orange juice; stability; physical properties
1. Introduction Colloids are a kind of important food additives, which are closely related to food quality and sensory quality. They function as foaming agents, edible coatings, thickeners, stabilizers, etc. The main reason for the wide use of colloids in the food
industry is their ability to absorb water and change the properties of food ingredients [1]. However, a large portion of the colloids used in the food industry is chemically synthesized, which poses potential hazards on public health. Guar is planted mainly in the semi-arid regions of South Asia with a large yield. Guar gum (GG), a natural polysaccharide, is obtained from the seed endosperm of the plant Cyamopsis tetragonolobus. It is a galactomannan, which consists of linear backbone chain of β-1,4-linked mannose units with α-1,6-linked galactose units (2:1) as a side chain [2]. Its unique chemical structure determines the GG has the ability of strong water absorption, a wide range of viscosity stability and good water solubility and crosslinking. Therefore, guar gum has wide applications in food products as a thickener, such as ice cream, sauces, instant foods, syrups, etc. GG can also be used as a soluble dietary fiber in food products, and the allowable daily intake (ADI) is 20 g [3,4]. Due to its high viscosity, the application of GG in food industry is limited, and physical properties of GG can be improved by the controlled partial enzymatic hydrolysis using acidic β-D-mannase, which hydrolyzes GG by selectively cutting mannose backbone chain, decreasing the molecular weight of GG significantly [3]. When dispersed in water, partial hydrolyzed guar gum (PHGG) with lower molecular weight gives low viscosity solution compared with its native chemical. Recently, GG, as a good source of water-soluble dietary fiber, has been studied extensively for its health benefits, like increase in defecating frequency and reduction in serum cholesterol, glucose concentration and free fatty acid [5,6], and it also can reduce glycemic response, inflammation and inflammatory bowel diseases [7,8]. Furthermore,
GG also can improve barrier properties and mechanical strength of nano-composites as biodegradable packaging film [9,10]. Orange, containing abundant organic chemicals and vitamin C, is one of the most productive fruits in the world, and orange juice is among the most popular and desirable products in the world. In order to maintain or increase the consistency and extend the shelf life of orange juice, carboxymethyl cellulose (CMC) is commonly used in fruit juice and other food industries due to its electrostatic repulsion between the CMC molecules so as to improve the stability [11]. However, most countries around the world have set up strict limits on chemically synthesized CMC. To the best of our knowledge, few studies related to the usage of GG in fruit juice are reported. The purpose of our study was to replace the partial amount of CMC by GG in fruit juice. In this context, the effect of GG on the physical stability, serum cloudiness (turbidity), sensory analysis, particle size distribution (PSD), aroma concentration and rheological properties of the orange juice were also evaluated.
2. Materials and methods 2.1 Materials GG used in this study was obtained from Romer Ltd. (Qingzhou, Shandong, China). Acidic β-D-mannase was obtained from Beijing micro-science Biotech Corp (Beijing, China). Xanthan gum, CMC and agar were obtained from Sangon Biotech Ltd (Shanghai, China). The oranges (Citrus sinensis) were purchased from Liqun Company of Qingdao and stored at the temperature of +7
and 80-90% humidity for
a maximum of 48 h before processing. 2.2 Enzymatic hydrolysis of GG GG was subjected to enzymatic hydrolysis using the acidic β-D-mannase (50,000 U) at 0.2 g/L. Firstly, distilled water was adjusted to pH 3 by adding citric acid [12]. After adding 20 g/L of GG powder into the solution, the solution was mixed under continuous magnetic stirring for 24 h at room temperature (25-28 ). After that, acidic β-D-mannase was added into the solution. During hydrolysis, GG solution was placed in a thermostatic water bath at 45
for 5, 25 and 40 min. And then the GG solution
was put into a thermostatic water bath at 80
for 20 min to terminate the enzymatic
reaction. Finally, a low viscous hydrolyzed GG solution was obtained and then lyophilized to get pure PHGG powder. 2.3 Determination of intrinsic viscosity and molecular weight The intrinsic viscosity was estimated using rheometer (AR2000ex, TA Instruments, USA) at 25
in a concentration of 2% for GG and PHGG. Before using
the rheometer, all of the solutions were prepared by dispersing GG powder and PHGG powder in a vortex of water under mild magnetic stirring for 30 min. After that, the solutions were placed for complete hydration for 12h at room temperature to reach maximum viscosity. When estimated the intrinsic viscosity, shear rate was set at 300s-1. The HPGPC-MALLS method was used to determine the molecular weight of GG and PHGG with different viscosity [13]. Three mg/ml aqueous solution of the samples were prepared, then filtered through 0.22 µm microporous membrane. The
determination of molecular weight was carried out using the Agilent Technologies 1260 HPLC (Agilent, Santa Clara, CA, USA). The flow rate was 0.6 ml/min, the injection volume was 100 µl, the mobile phase was sodium sulfate solution (0.1M), and the column temperature was set at 35 . The column consisted of two columns in tandem: HQSB 804 and HQSB 802.5 (Showa Denko Corporation, Tokyo, Japan). And the detector was DAWN HELEOS
eighteen angle laser instrument (Wyatt, Santa
Barbara, CA, USA). The standard curves of viscosity and molecular weight was made. 2.4 Preparation of orange juice samples Firstly, the oranges were washed and sliced. Secondly, the prepared oranges were divided into several parts and put into the electric juicer. Next, the orange juice was filtered through four layers of gauze to separate pulp suspensions and tissue components. Finally, the orange juice was poured into the 250 ml conical flask. 2.5 Effect of GG and PHGG on the stability of orange juice 2.5.1 Single factor The orange juice samples (150 ml) were placed in 250 ml conical flasks, respectively. 0.1%, 0.3%, and 0.5% of GG (584 mpa·s) and PHGG (3.3 mpa·s, 54 mpa·s, 151.4 mpa·s) were added to the samples, respectively. After homogenization for 1 min, the samples were put in refrigerators (4 ) for 24 h. The stability of orange juice was assessed by serum cloudiness (turbidity). Forty ml of the stored juice were added into 50 ml centrifuge tubes, and then centrifuged at 4000 r/min for 15min at 25
(Zhao Di Biological Technology, Shanghai, China). The
supernatant was diluted by 1 time and then measured by the UV-visible spectrophotometer (Shanghai Precision Scientific Instrument, Shanghai, China) calibrated with distilled water. The absorbance at 660 nm was directly related to the turbidity of orange juice [14]. 2.5.2 Effect of GG and other colloids on the stability of orange juice The orange juice samples (150 ml) were placed in conical flasks. GG (584 mpa·s) was combined with CMC (0.03%, 0.05%), agar (0.1%, 0.15%, 0.2%) and xanthan gum (0.03%, 0.06%), respectively. Then the mixture of colloids was added into the orange juice, homogenized for 1min, and put in refrigerators (4 ) for 24 h. The stability of orange juice was also assessed by the serum cloudiness (turbidity). 2.6 Effect of GG on physical properties and stability of orange juice 2.6.1 Sensory analysis Orange juice was prepared at room temperature with four different formulations and the other one was a control group with no colloid. The five orange juice samples were evaluated by a trained descriptive panel. This panel was composed of nine highly trained people (four males and five females, within the age of 20-30 years), each of them had more than 100 h of experience in evaluation of orange juice. The panelists were trained on flavor attributes before the actual evaluation. The different coded samples were tasted by each assessor. The acceptance testing of attributes (appearance, flavor, aroma, texture, overall impression) using a 20-point hedonic scale (1 means disliked very much and 20 means liked very much) was performed on the orange juice. Orange juice was evaluated in duplicate by every assessor. Drinking
water at room temperature to clean mouth before and between evaluations of the orange juice. Finally, the average score and total score were calculated. 2.6.2 Particle size distribution (PSD) The PSD of orange juice was determined by the Laser Particle Size Distribution Analyzer (Malvern Zetasizer, England). The aforementioned four formulations and the control group were diluted by taking one ml into nine ml water, after thoroughly mixing the samples were put into the Analyzer to measure the PSD. In addition to the particle size distribution, the volume-based mean diameter (D[4,3] Eq. (1)) was evaluated [14]. Through its particle size distribution and the volume-based mean diameter (D[4,3]), the stability of orange juice can be judged. D[4,3]= ΣniDi4/ΣniDi3
(1)
Where ni is the percentage of particles with a diameter Di. 2.6.3 Aroma analysis by Gas chromatography-mass spectrometry (GC-MS) A carboxen/polydimethylsiloxane fiber (100 µm PDMS Supelco, Bellefonte, USA) was selected for aroma analysis, as suggested in previous studies [15]. The solid-phase micro extraction (SPME) fiber was conditioned in the injector of an Agilent Technologies 6890N/5973i network (GC-MS) system (Agilent, Santa Clara, USA) at 250
for 1 h before starting extraction [16]. Five ml of the respective
aforementioned four samples was transferred into the 20 ml headspace vial, 1.8 g NaCl was added to facilitate the volatile components in the volatile sample, and internal standard (2 µl cyclohexanone) was also added to each vial before SPME analysis. The silicone PTFE septa was used to sealed the vials containing the mixtures
and held the vials on a magnetic stirrer at 40
for 15 min, after that the activated
SPME extraction head was inserted into the vial bottle, headspace absorbed for 40 min. After that, the fiber was then inserted into the injection port at a depth of 4 cm for the complete desorption, each test was run three times in parallel. The aroma analysis was carried out by a HP-5MS column (30 m×0.25 mm, 0.25 µm; Agilent, Santa Clara, CA, USA). The initial temperature of the GC oven was set
at 50
for 2 min, and was then increased at a speed of 5 /min until it reached 250 ,
where it was held for 5 min. The carrier gas was high-purity helium, and a flow rate was set at 1 ml/min under the constant flow mode. The injection port was heated at 250
under the splitless injection mode. The mass spectrometer was progressed
positive electron impact ionization mode (EI+, 70ev) and the mass scan range from 40 m/z to 450 m/z. The cyclohexanone was used as internal standard for quantitative analysis, to assume the response frequency of each aroma was the same as the internal standard, the amount of each substance was calculated by Eq. (2). M= (A1×M0)/ (A0×V)
(2)
Where M is the content of substance to be measured (µg/ml), A0 is the quality of the internal standard (µg), A1 is the peak area of the material to be measured, M0 is the peak area of the internal standard (µg), and V is the volume of sample (ml). 2.6.4 Rheological characteristic analysis of orange juice As the fruit juice are composed by an insoluble phase dispersed in a viscous solution, the rheological was carried out on orange juice. The rheological characteristic analysis of orange juice was carried out using the rheometer (AR2000ex,
TA Instruments, USA). The temperature of measured was maintained constantly at 25
using a Peltier system, and each sample was analyzed three times. The orange
juice samples were firstly placed in the rheometer and maintained for 1 min before shearing. After that, the shear stress and intrinsic viscosity were recorded with the shear rate changed from 0.1 s-1 to 100 s-1, the flow curve for orange juice with five different formulations was made and analyzed. 2.7 Statistical analysis All data analysis, including serum cloudiness, the score of sensory analysis, particle size distribution, aroma concentration and the rheological characteristics, were presented as the mean ± standard deviations (SD). Paired t-tests and linear regression were performed using IBM SPSS Statistics version 19.0. P≤0.05 was the level of significance. And each experiment was repeated at least three times.
3. Results and discussion 3.1 The determination of intrinsic viscosity and molecular weight By measuring the intrinsic viscosity and molecular weight of GG, the relationship between intrinsic viscosity and molecular weight was calculated. The intrinsic viscosity of GG exhibited a linear relationship with molecular weight of GG, and its linear equation was y=4.3145x+77.168 (R2=0.9978, where x was intrinsic viscosity (mpa·s), y was molecular weight (kDa)) (Fig. 1.). According to this equation, the intrinsic viscosity 3.3 mpa·s, 51.4 mpa·s, 154 mpa·s and 584 mpa·s were corresponded to 71 kDa, 275 kDa, 816 kDa and 2,580 kDa, respectively. 3.2 Single factor of GG and PHGG
To judge whether the orange juice was in a steady state, the serum cloudiness (turbidity) was used as the evaluation index. The greater the serum cloudiness, the better stability of the orange juice. Generally speaking, when the serum cloudiness at the range of 0.95~1.35, the stability of orange juice is commonly accepted. Table 1 showed the serum cloudiness (turbidity) of different concentration and viscosity of GG and PHGG, where significant variations of serum cloudiness in relation to the concentration and viscosity were observed (p<0.01). The serum cloudiness of the sample with a concentration of 0.1% and viscosity of 3.3 mpa·s was the lowest, the GG with a concentration of 0.5% and viscosity of 584 mpa·s was the biggest; furthermore, the turbidity increased with the increasing of GG concentration and viscosity. The stability of orange juice is reflected by the value of turbidity. Before the evaluation, the orange juice samples were centrifuged at first, and only the supernatant was put into the spectrophotometer to evaluate its absorbance [14]. The absorbance is only associated with the orange juice sample turbidity, being the suspended particles responsible for the absorption of radiation. According to the Stokes Law (Eq. (3)), the larger size particles are easier to precipitate, and the smaller size particles tend to remain in the supernatant after centrifugation. A good thickener can prevent the formation of large polymers. The different absorbance values were mainly influenced by the particles that remained in suspension, as observed in Table 1. In Table 1, it was obviously that GG with viscosity of 584 mpa·s was the best, and the greater the concentration of GG, the greater the serum cloudiness. So, the GG with the
viscosity of 584 mpa·s was chosen to be assessed in the next steps. V0= (dp2 (Ps-Pf) g)/18Vf
(3)
Where V0 is Settling velocity of particles (cm/s); dp is Diameter of particles (cm); Ps is Density of particles (g/cm3); Pf is Fluid density (g/cm3); Vf is Fluid viscosity (Pa); and g is Acceleration of gravity (9.8m/s2). 3.3 Effects of mixtures of GG and several colloids The effect of mixtures of GG and several colloids on orange juice was also evaluated by turbidity. It was obviously that the turbidity of 0.5% GG mixed with other colloid was the biggest of all the formulations (p<0.01), and 0.1% GG mixed with other colloid was the lowest (p<0.01) (Fig. 2). The turbidity was correlated with the concentration of GG. From Fig. 2, the serum cloudiness (turbidity) of orange juice with 0.5% GG was the biggest. However, the orange juice with 0.5% GG would make the juice sticky and affect the taste, so the 0.5% GG was abandoned. On the other hand, the serum cloudiness of orange juice with 0.12% CMC was 1.276, and 0.12% CMC was the amount that added in most of factories, so it was taken as the standard. The low turbidity reflected the characteristics of the orange juice that were unstable, but the high turbidity reflected orange juice were too sticky. Taking into account their stability and cost, four formulations were chosen at last, they were: (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum. All of the following experiments were carried out with the 4 formulations and a
control group which was only orange juice. 3.3 Sensory analysis The acceptance of orange juice formulations was shown in Table 2. The score of 0.1% GG combined with 0.03% CMC was the highest, and its effect was significantly better than the other formulations (p<0.01), indicating the orange juice which was added with 0.1% GG combined with 0.03% CMC was better than orange juice with no colloid, in terms of their appearance, flavor, or texture. In contrast, the presence of 0.3% GG combined with 0.03% xanthan gum was the worst, maybe because orange juice that added this formulation was too sticky and a large amount of bubbles existed on the juice liquid surface, these would affected people’s taste. Acceptance of the products with colloid is important because consumers aren’t interested in consuming orange juice which is stratification and has a large amount of bubbles. Acceptance scores for appearance was between 14 and 19 on a hedonic scale of 20 points, indicating that consumers liked the products. Since aroma of juice is the most important factor that affect the orange juice, all consumers like orange juice with good flavor and aroma. In terms of the texture, it is also an important factor, generally soft texture is easy to accept by human. However, the formulation of (C) and (D) made the orange juice sticky, therefore, the colloid that added to orange juice should keep the original taste of juice. It was obviously that (A), 0.1% GG combined with 0.03% CMC, was the best formulation, people liked this even than the orange juice with no colloid. Therefore, based on the sensory analysis, the best formulation was 0.1% GG combined with 0.03% CMC.
3.4 Particle size distribution Fig. 3 showed the particle size distribution (PSD) of the orange juice with five different formulations. It could be seen that the PSD of the samples (A), (B), (D) were similar, all of them had two peaks, and they were different from samples (C) and (E) which only had one peak. Fig. 4 showed the mean particle diameter based on the volume (D[4,3]) for the evaluated samples. It was noteworthy that the mean particle diameter of orange juice with colloid was higher than the orange juice with no colloid (p<0.01). And the mean particle diameter of orange juice with GG and xanthan gum were higher than the others (p<0.01). It is well-known that the main reason for fruit juice precipitation is the existence of some insoluble material such as pulp, because of the difference between the density of insoluble material and fruit juice, these substances are easier to precipitate under the influence of gravity. According to the Stokes Law (Eq. (3)), the downward gravity of each particle should be equal to the sum of the buoyancy force and the frictional resistance of the medium. The Eq. (3) is suitable for the particle diameter bigger than 2 µm, and the pulp is in line with the conditions of the formula particles. From this formula, settling velocity is related to particle diameter, particle density, medium viscosity and medium density. The main way to improve the stability of orange juice are to adjust the particle radium and increase the viscosity of liquid. From Fig. 3, it could be seen that (A), (B) and (D) had two peaks, one of the peak height was 1080 nm, the other was 4300 nm, and there was no overlap between the two peaks. However in terms of
samples (C) and (E), it only had one peak which peak height was 3600 nm. The differences between samples’ peak maybe due to the components of samples with good stability could distribute evenly and didn’t produce any precipitation, so each peak could represent the individual components of the sample. In contrast, the components of samples with bad stability could aggregate together and form a macromolecular polymer, so there was only one peak that represented the polymer peak. On the other hand, according to Eq. (3), the smaller particle size of the juice, the more stable it is. Although the mean particle diameter based on the volume (D[4,3]) of samples which added the GG were higher than the samples that added no colloid, the stability of them was also better than the samples that added no colloid. In conclusion, by adjusting the mean particle diameter and increasing the viscosity of liquid, 0.1% GG combined with 0.03% CMC (A) and 0.3% GG combined with 0.1% agar (B) would provide better formulations. 3.5 Aroma analysis in the 5 orange juice samples The SPME-GC-MS technology was used to detect the difference of aroma components in orange juice which added different formulations. Table 3 showed the content of main ion chromatograms of aroma compounds in the orange juice. A total of 31 aroma compounds were identified in the headspace of orange juice (Table S1). The most abundant aroma compound was 2-methyl-cyclopentanone, up to 50%. Analysis of the volatile composition of orange juice showed that ketones and alkenes were the most representative compounds aroma in all chromatographic profiles for all of the five different formulations, accounting for more than 90% of the total volatile
fraction. Previously, Tietel et al had reported that limonene, linalool, α-pinene, decanal and butanoic acid ethyl ester were the important aroma compounds [17]. Terpene is an important group of aroma compounds in orange juice, including limonene, α-pinene, α-panasinsen and caryophyllene. There is a large amount of limonene in orange juice which belongs to single terpenoids with a light lemon flavor and active chemical property. In this study, the content of limonene in the formulations of (A), (B), (C) and (D) were all lower than (E) (p<0.01), indicating that GG maybe inhibit the volatilizations of limonene. In considering to the α-pinene, its content in the formulation (A) was higher than that in the other 4 formulations (p<0.01), but the content of α-pinene in other 4 formulations were the same basically, indicating that GG maybe had no effect on the volatilizations of α-pinene. And in terms of α-panasinsen, the formulations of (A), (B) and (D) were higher than (E) (p<0.01), indicating that GG maybe promoted the volatilizations of it. And as for the caryophyllene was concerned, the content of it in formulations (A), (B), (C) and (D) were all higher than (E) (p<0.01), indicating that GG maybe also promoted the volatilizations of caryophyllene. Linalool is the main alcohol in orange juice with a mellow fragrance of flowers, it has an important contribution to the abundant aroma of orange juice. And its chemical property is active, it can produce α-terpineol by a series of reaction under certain conditions. The content of linalool in the formulations that was added with colloid was all higher than that in the control group (p<0.01), indicating that GG
maybe had a good effect on its release. Decanal is the characteristic aroma component of orange juice with a typical fruity, but it was only detected in formulation (A). And butanoic acid ethyl ester is a common aroma in orange juice, it is the most important ester aroma too. However, the content of butanoic acid ethyl ester in the formulations (A), (B), (C) and (D) were lower than the control group, but the difference of it was not obvious, indicating that GG maybe had a slight inhibitory effect on its release. Among the total aroma compounds isolated (31), 13 of them had no significant differences compared with the control group. The rest of compounds (18) were significantly influenced by GG, including limonene, linalool, α-pinene, decanal and butanoic acid ethyl ester. In general, most of the aroma compounds were presented at a low concentration. This showed the GG have an effect on the release of aroma compounds. Considering the differences aroma compounds between these formulations, it was obviously that the aroma compounds of formulation (A) was better than the others both on the characteristic aroma and other aroma compounds. 3.6 Rheological characteristic analysis of orange juice Rheological behavior of five different formulations orange juice was analyzed at 25 . The curve of shear stress-shear rate was shown in Fig. 5 and the curve of viscosity-shear rate was shown in Fig. 6, the 5 curves in those figures represented the 5 different formulations, respectively. All of the orange juices showed pseudo plastic behavior, indicating that added colloids to the orange juice won’t change the rheological properties of it. In Fig. 5, the rheological properties of different thickening agents could be clearly observed, the shear stress was also increasing with the
increase of the shear rate, but the ratio of shear stress and shear rate was decreasing with the increase of shear rate. Therefore, the orange juice that added thickening agent was a typical shear thinning system, and the juice with no colloid didn’t change significantly. The change of viscosity in different shear rate of orange juice with different thickening agents was shown in Fig. 6. In contrast to the shear stress, with the increase of shear rate, the viscosity of the orange juice became smaller. The viscosity of the orange juice that added 0.3% GG combined with 0.03% xanthan gum was the largest at the same shear rate, and the viscosity of the orange juice that added 0.1% GG combined with 0.03% CMC was the smallest. However, the viscosity of the control group had no change, and it belonged to newton fluid. Considering the effects of different thickening agents on several main aroma substances in orange juice, there was no direct relationship between the viscosity and the aroma released from the orange juice, which was the same with the other studies. Bylaite et al had reported that the acting force of the aroma compounds and the xanthan gum was determined by the physical and chemical properties of the aroma substance, but not with the viscosity of the solution, and added the thickener even promoted the volatilize of aroma substance [17,19]. In the same way, Siefarth et al also pointed out that the relationship between solution viscosity and aroma release was not significant in low viscosity solutions [20].
4. Conclusions The present work evaluated the effect of GG and its combination with other
colloids on the stability and physical properties of orange juice. Based on the results from serum cloudiness, sensory analysis, particle size distribution, aroma analysis and rheological characteristics analysis, it was concluded that 0.1% GG combined with 0.03% CMC will form the best formulation. It can be concluded that the GG may have the potential to be utilized as a thickening agents that added to the orange juice. So when it is added to the fruit juice, it can prevent the fruit juice from stratification and precipitation, and it also makes the product have a good creamy taste. On the other hand, the GG can successfully be used as a source of soluble dietary fiber due to its functional properties [12]. Therefore, the GG can be widely used in orange juice as it will not affect the quality of orange juice, and it can significantly reduce the concentration of CMC.
Acknowledgment This research was supported by the National Natural Science Foundation of China (31471657).
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[12] D. Mudgil, S. Barak, B.S. Khatkar, Effect of enzymatic depolymerization on physicochemical and rheological properties of guar gum. Carbohydr. Polym. 90 (2012) 224-228. [13] C. Yang, Y. Gou, J. Chen, J. An, W. Chen, F. Hu, Structural characterization and antitumor activity of a pectic polysaccharide from Codonopsis pilosula. Carbohydr. Polym. 98 (2013) 886-895. [14] M.L. Rojas, T.S. Leite, M. Cristianini, I.D. Alvim, P.E.D. Augusto, Peach juice processed by the ultrasound technology: Changes in its microstructure improve its physical properties and stability. Food Res. Int. 82 (2016) 22-33. [15] R.B. Mastello, N.S. Janzantti, M. Monteiro, Volatile and odoriferous compounds changes during frozen concentrated orange juice processing. Food Res. Int. 77 (2015) 591-598. [16] M.K. Kim, M.Y. Kim, K.G. Lee, Determination of furan levels in commercial orange juice products and its correlation to the sensory and quality characteristics. Food. Chem. 211 (2016) 654-660 [17] Z. Tietel, R. Porat, K. Weiss, D. Ulrich, Identification of aroma-active compounds in fresh and stored ‘Mor’ mandarins. Int. J. Food Sci. Tech. 46 (2011) 2225-2231. [18] E. Bylaite, J. Adler-Nissen, A.S. Meyer, Effect of xanthan on flavor release from thickened viscous food model systems. J. Agric. Food Chem. 53 (2005) 3577-3583 [19] E. Bylaite, Z. Ilgunaite, A.S. Meyer, J. Alder-Nissen, Influence of λ-canageenan on the release of systematic series of volatile flavor compounds from viscous food
model systems. J. Agric. Food Chem. 52 (2004) 3542-3549. [20] C. Siefarth, O. Tyapkova, J. Beauchamp, U. Schweiggert, A. Buettner, S. Bader, Influence of polyols and bulking agents on flavor release from low-viscosity solutions. Food. Chem. 129 (2011) 1462-1468.
Figure Captions: Fig. 1. The relationship between intrinsic viscosity and molecular weight distribution. Error range of all values were between ±5%- 20%. Vertical bars represent the standard deviation. Fig. 2. The serum cloudiness of different concentration GG with other colloid on orange juice. (A) 0.1% 584mpa·s GG; (B) 0.3% 584mpa·s GG; (C) 0.5% 584mpa·s GG. Vertical bars represent the standard deviation. Fig. 3. Particle Size Distribution of the orange juice with 5 different formulations. (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group. Fig. 4. Mean particle diameter for volume-based mean diameter (D[4,3]). Vertical bars represent the standard deviation. (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group. Fig. 5. Effect of shear rate on shear stress of orange juice with 5 different formulations. (█) 0.1% GG combined with 0.03% CMC; (●) 0.3% GG combined
with 0.1% agar; (▲) 0.3% GG combined with 0.03% xanthan gum; (★) 0.1% GG combined with 0.06% xanthan gum; (◆) control group. Fig. 6. Effect of shear rate on viscosity of orange juice with 5 different formulations. (█) 0.1% GG combined with 0.03% CMC; (●) 0.3% GG combined with 0.1% agar; (▲) 0.3% GG combined with 0.03% xanthan gum; (★) 0.1% GG combined with 0.06% xanthan gum; (◆) control group.
Fig. 1. The relationship between intrinsic viscosity and molecular weight distribution. Error range of all values were between ±5-20%. Vertical bars represent the standard deviation.
c
a
b e
d
f
e
d
e
c
a
f
b
f
a
d
d
c g
e
b
Fig. 2. The serum cloudiness of different concentration GG with other colloid on orange juice. (A) 0.1% 584mpa·s GG; (B) 0.3% 584mpa·s GG; (C) 0.5% 584mpa·s GG. Vertical bars represent the standard deviation.
Size Distribution by Volume
(A)
Volume (Percent)
20 15 10 5 0 0.1
1
10
100
1000
10000
Size (d.nm)
Record 1: 1 1
Size Distribution by Volume
(B)
Volume (Percent)
15
10
5
0 0.1
1
10
100
1000
10000
Size (d.nm)
Record 3: 2 2
Size Distribution by Volume
(C)
Volume (Percent)
30
20
10
0 0.1
1
10
100 Size (d.nm)
Record 7: 3 3
1000
10000
Size Distribution by Volume
(D)
Volume (Percent)
20 15 10 5 0 0.1
1
10
100
1000
10000
Size (d.nm)
Record 10: 4 3
Size Distribution by Volume
(E)
Volume (Percent)
20 15 10 5 0 0.1
1
10
100
1000
10000
Size (d.nm)
Record 14: 6 1
Fig. 3. Particle Size Distribution of the orange juice with 5 different formulations. Formulation: (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group.
b c
a
d e
Fig. 4. Mean particle diameter for volume-based mean diameter (D[4,3]). Vertical bars represent the standard deviation. (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group.
Fig. 5. Effect of shear rate on shear stress of orange juice with 5 different formulations. (█) 0.1% GG combined with 0.03% CMC; (●) 0.3% GG combined with 0.1% agar; (▲) 0.3% GG combined with 0.03% xanthan gum; (★) 0.1% GG combined with 0.06% xanthan gum; (◆) control group.
Fig. 6. Effect of shear rate on viscosity of orange juice with 5 different formulations. (█) 0.1% GG combined with 0.03% CMC; (●) 0.3% GG combined with 0.1% agar; (▲) 0.3% GG combined with 0.03% xanthan gum; (★) 0.1% GG combined with 0.06% xanthan gum; (◆) control group.
Table 1 The turbidity of different composition guar gum on the orange juice. Concentration Viscosity 0.1%
0.3%
0.5%
3.3 mpa·s
0.518±0.04Cd
0.631±0.02Bd
0.689±0.06Ad
51.4 mpa·s
0.713±0.05Cc
0.721±0.04Bc
0.750±0.03Ac
154 mpa·s
0.835±0.03Cb
0.865±0.07Bb
0.970±0.06Ab
584 mpa·s
1.042±0.03Ca
1.072±0.06Ba
1.429±0.05Aa
Data were shown as means ± standard deviation followed by different upper case and lower case letters indicate significant differences at p ≤ 0.05 between different rows and columns, respectively.
Table 2 Acceptance of the orange juice formulations.
Formulation Parameter (A)
(B)
(C)
(D)
(E)
Appearance
18.4±0.5a
17.2±0.4b
14.4±0.7c
14.4±0.3c
14.7±0.5c
Flavor
18.9±0.6a
17.2±0.3b
16.1±0.6c
14.8±0.5d
17.8±0.2b
Aroma
12±0.3b
10.1±0.5c
8.9±0.2d
10.3±0.3c
13.8±0.3a
Texture
13.9±0.8a
13.4±0.6a
10±0.3d
11.8±0.4c
13.1±0.7b
Overall impression
12.8±0.4a
10.6±0.4c
10.1±0.7c
11.2±0.6b
12.2±0.5a
Total score
76±0.3a
68.5±0.3c
59.5±0.8e
62.5±0.5d
71.6±0.7b
Hedonic values (appearance, flavor, aroma, texture and overall impression): 1-disliked very much; 20-liked very much. Formulation: (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group Data were shown as means ± standard deviation followed by different lower case letters indicate significant differences at p ≤ 0.05 between different columns.
Table 3 The main aroma compounds of orange juice formulations. Aroma
Formulation
compound
(A)
(B)
(C)
(D)
(E)
Butanoic acid, 2.19±0.16b
2.18±0.04b
2.26±0.03a
2.02±0.08c
2.29±0.05a
68.21±0.29a
41.58±0.12c
49.87±0.11b
35.11±0.05e
38.01±0.08d
0.36±0.07a
0.22±0.03b
0.24±0.04b
0.26±0.03b
0.23±0.03b
0.74±0.16a
0.48±0.05d
0.55±0.03c
0.47±0.04d
0.62±0.02b
45.24±0.39b
35.29±0.07d
34.87±0.06e
36.81±0.04c
53.19±0.05a
0.28±0.03a
0.21±0.02b
0.22±0.01b
0.21±0.03b
0.16±0.01c
Decanal
0.21±0.02
N/D
N/D
N/D
N/D
Caryophyllene
0.16±0.02b
0.13±0.01b
0.15±0.02b
0.21±0.03a
0.07±0.01c
Linalool
0.71±0.07a
0.44±0.07b
0.49±0.05b
0.41±0.08bc
0.35±0.03d
α-panasinsen
0.30±0.04b
0.27±0.02b
N/D
0.39±0.03a
0.19±0.02c
ethyl ester 2-methyl-cyclop entanone α-pinene Hexanoic acid,ethyl ester Limonene Octanoic acid, ethyl ester
Formulation: (A) 0.1% GG combined with 0.03% CMC; (B) 0.3% GG combined with 0.1% agar; (C) 0.3% GG combined with 0.03% xanthan gum; (D) 0.1% GG combined with 0.06% xanthan gum; (E) control group Data were shown as means ± standard deviation followed by different lower case letters indicate significant differences at p ≤ 0.05 between different columns.