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Preparation and properties of granular cold-water-soluble porous starch
Journal Pre-proof Preparation and properties of granular cold-water-soluble porous starch
Yun Chen, Guifang Dai, Qunyu Gao PII:
S0141-8130(19)39367-5
DOI:
https://doi.org/10.1016/j.ijbiomac.2019.12.060
Reference:
BIOMAC 14087
To appear in:
International Journal of Biological Macromolecules
Received date:
17 November 2019
Revised date:
2 December 2019
Accepted date:
7 December 2019
Please cite this article as: Y. Chen, G. Dai and Q. Gao, Preparation and properties of granular cold-water-soluble porous starch, International Journal of Biological Macromolecules(2019), https://doi.org/10.1016/j.ijbiomac.2019.12.060
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© 2019 Published by Elsevier.
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Preparation and properties of granular cold-water-soluble porous starch Yun Chen, Guifang Dai, Qunyu Gao* Carbohydrate Laboratory, School of Food Science and Engineering, South China University of Technology, No. 381, Wushan Road, Guangzhou 510640, China
*
Corresponding author. Tel: +86-13660261703; Fax: +86-20-87113848
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Email: [email protected], [email protected]
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Journal Pre-proof Highlights 1. Granular cold-water soluble porous starch was prepared from porous waxy corn starch 2. PS was easier to prepare P-GCWS than WS prepared N-GCWS 3. The surface area of P-GCWS was higher than that of N-GCWS
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4. The oil absorption capacity of P-GCWS was higher than that of N-GCWS
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Journal Pre-proof Abstract: In this work, granular cold-water soluble waxy corn starch (N-GCWS) and granular coldwater soluble porous waxy corn starch (P-GCWS) were prepared by waxy corn starch (WS) treated with alcohol-alkali. Starch morphologies, crystal structures, turbidity, cold water viscosity, freeze-thaw stability and oil absorption capacity of N-GCWS and P-GCWS starches were compared. The results showed porous waxy corn starch (PS) was easier to prepare P-GCWS starch than WS to prepare N-GCWS. SEM showed that PS and WS became dent-twisted and tended to flatten with the increase of CWS. After alcohol-alkali treatment, the X-ray diffraction pattern of PS and WS changed from A type to amorphous and pores were remained on the surface of P-GCWS starches granular.
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Turbidity, freeze-thaw stability, viscosity, oil absorption capacity of N-GCWS and P-GCWS starches
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was shown higher than that of WS and PS. The oil absorption capacity of P-GCWS was higher than
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that of N-GCWS.
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Keywords: waxy corn starch, porous starch, granular cold-water soluble starch, absorption capacity
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Introduction Starch is the most important carbohydrate which widely used in the human nutrition and industry such as gelling agent, thickening agent, bulking agent, stabilizer and Pickering emulsions [1-3]. Although starch is hydrophilic because it contains a large amount of hydroxyl groups, the native starch is water insoluble at room temperature thus native starch cannot play as thickener, gelling agent and water binder. Therefore, many studies have been focused on the development of starch denaturation and its derivatives. Cold-water-soluble starches, such as pregelatinized starches
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which would absorb water and promote viscosity at room temperature, are being developed to broaden the application of starch [4, 5]. Drum drying and extrusion are often used to prepare
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pregelatinized starches [6, 7]. However, the pregelatinized starches made by drum drying show
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rough and poor flexibility which not match the quality of instant foods. Granular cold-water soluble (GCWS) starches are also one of the cold-water-soluble starches. Compared with the pregelatinized
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starches, GCWS starches give higher viscosity and smoother texture.
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Jane et al. [8] described a process for preparing GCWS starches using aqueous alcohol treatment at high temperature. Dries ed al [9] treated the maize starch starches with aqueous ethanol
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treatments at elevated temperatures and atmospheric pressure to prepare GCWS starches and found that ethanol concentrations had great influence on the preparation of the GCWS starches. The
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ethanol-alkali method is widely used to preparing GCWS starches, because it can be used to various native starch to prepare GCWS starches at ambient temperature and pressure [10, 11]. The hydroxyl group on the starch molecule has a negative charge in the strong alkali environment. When the concentration of the alkali solution is gradually increased, more and more negatively charged hydroxyl bands cause the hydrogen bond between the starch molecules to break, and double helical of the starches becomes a single helix [12]. The presence of alcohol not only restricts swelling of starch granules by decreasing the effective water concentration but also acts as a complexing agent to stabilize the dissociated starch chains [13]. During the drying process, the volatilization of ethanol causes a cavity to form inside the starch, then GCWS starches have intact particles and good solubility. GCWS starches can be used in many food products as thickening agents. Moreover, GCWS starches can also be used to encapsulating materials, such as encapsulation of ethylene gas [14] and encapsulation of atrazine [15]. 4
Journal Pre-proof Porous starch has abundant micro-sized pores from the surface extending to the center. The porous starch exhibits a "sponge" structure which allows the starch to have a large specific surface area and specific pore volume, so the adsorption capacity is greater than that of the native starch [16]. Substance can easily adhere firmly to the inner wall of the porous starch, moreover some substances that are unstable to temperature, light and oxygen can be protected by porous starch. Therefore, porous starch can be used as an adsorbent in many areas such as food, medicine, chemical industry and agriculture. Zhang ed. al [16] had been used the porous corn starch which prepared by α-amylase and glucoamylase hydrolysis as adsorbent adsorbing methyl violet. Glen ed al [17] described that
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porous starch microspheres prepared from high-amylose corn starch encapsulate essential plant oils
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and yet remain an easily dispersed powder. Porous starch can also encapsulate grape seed proanthocyanidins and Lactobacillus plantarum [18, 19].
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Here, P-GCWS starches were prepared from porous waxy corn starch by ethanol-alkali
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treatment. To the best of our knowledge, this is the first report on the preparation and properties of
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P-GCWS starches. After treated by alcohol-alkali, not only the encapsulation but also the water solubility of the porous starch would be significantly improved. Thereby the range of porous starch
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in the food industry would be significant expanded. Starch morphologies, crystal structures, turbidity, freeze-thaw stability, cold water viscosity and oil absorption capacity of N-GCWS and P-GCWS
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starches were comparative studied in this work. The results show that after treated by alcohol-alkali, there were still many porous in the surface of the porous starch granules. PS was easier to prepare P-GCWS starches than WS because of higher surface area. Oil absorption capacity of P-GCWS starches was higher than that of N-GCWS starches. This means the large specific surface area and excellent encapsulation of porous starch can be maintained after alcohol-alkali treatment.
2 Materials and methods 2.1 Materials Waxy corn starch was donated by Qinhuangdao Lihua Starch Co., Ltd, China. Amyloglucosidase (23 units/mg) and α-amylase (16 units/mg) were purchased from Sigma-Aldrich Chemical Company, USA. Absolute ethanol, hydrochloric acid and sodium hydroxide were sought from Guangzhou Chemical Reagent Factory. Sodium acetate and glacial acetic acid were purchased from Shanghai Runjie Chemical Reagent Co., Ltd. Chemicals and solvents used in this work were 5
Journal Pre-proof analytical grade. 2.2 Preparation of N-GCWS and P-GCWS The waxy maize porous starch were prepared according to Zhang [16] with some modifications. Briefly, waxy maize starch suspensions (100 g, 30%) were prepared with sodium acetate buffer (pH=5.5). The suspensions were kept under 100 rpm mechanical stirring at 50 °C for 1h, then 1.5g mixed enzyme (α-amylase: amyloglucosidase = 3:1) was added to the suspensions. After 12 h of reaction at 50 °C, the solution was adjusted to pH = 10 with NaOH (1 M) solution. The suspensions
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were washed by successive centrifugation with distilled water to pH nearly 7. The N-GCWS and P-GCWS starch were prepared according to Chen et al.[15]. Typically,
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waxy maize starch (5g, dry weight basis) suspensions and porous starch (5g, dry weight basis)
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suspensions were prepared with absolute ethanol. After the prepared suspension was placed in a 25 ° C water bath and stirred uniformly, sodium hydroxide solution (3M) was added slowly to the
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suspensions (4 mL/min). After the required NaOH was added, continue stirring for a certain period
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of time, then pour out the supernatant. 80% ethanol solution was added to the sample and the pH was adjusted to neutral with hydrochloric acid solution. The sample was washed with anhydrous ethanol
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several times. 2.3 Cold water solubility
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The method of determined cold water solubility (CWS) was according to Eastman and Moore [20] with some modification. Typical, 100 mL distilled water was added to a bender beaker. The starch samples were added into the blender operated at a low speed (500 rpm) for 30 s. Then the blender was switched to a high speed (1000rpm) for 2 min. The starch suspension was transferred to a centrifuge cup and centrifuge at 3100 rpm for 15 min. 25 mL aliquot of the supernatant was transferred to a tared petri dish and dried in an oven at 120℃ to constant weight. The CWS was calculated by eqn. (1): CWS(%) =
grams of solids in supernatant×4 grams of samples
× 100%
(1)
2.4 Polarized light microscopy Native and GCWS starch suspensions (water-glycerol 50:50 v/v) were observed under crossed polarized light (magnification 200×) using a binocular microscope (Eclipse 80i, Nikon Inc., Melville, 6
Journal Pre-proof NY, USA) equipped with real time viewing (Q-capture Pro, Q-Imaging, BC, Japan). A Q-Imaging digital camera (QICAM fast 1394, BC, Japan) was used for image capture. 2.5 Scanning Electron Microscopy (SEM) Scanning electron microscopy (SEM) was used to analyze the micro-morphology of native and modified maize starch. Starch samples were scattered on double-sided adhesive tape attached to a circular aluminum stub, and coated with 20 NS gold under vacuum. After then, the samples were viewed and photographed with a scanning electron microscope (model EVO 18, Zeiss, Germany) at
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an acceleration potential of 20 kV.
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2.6 X-ray diffraction (XRD) pattern
The samples were first placed in a dryer at a relative humidity of 15% for 24 h to ensure that all
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samples had the same moisture content. The X-ray diffraction (XRD) patterns of different samples
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were obtained with a D/Max-2200 X-ray diffraction (Rigaku Denki Co., Tokyo, Japan) using Cu Kα radiation at 44 kV and 26 mA. The diffraction angle ranged from 4° to 40° (2θ) at the rate of 5°/min
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(Yanika, Chureerat, Vilai, & Dudsadee, 2009). Relative crystallinity was calculated based on the
Komiya, 1983).
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2.7 Turbidity measurements
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method described by the ratio of crystalline area to total diffractogram area (Nara, Sakakura, &
The measurement of turbidity was according to Perera et al. [21]. The native starch and porous starch were added to water to prepare starch suspensions with different concentrations (1% w/w, 2% w/w, 3% w/w), and the mixture was heated in a boiling water bath for 30 minutes under constant stirring. N-GCWS and P-GCWS starches was slowly added to distilled water under low-speed stirring for 10min, and then stirred under high-speed stirring for 20 min to dissolve in water to prepare starch dispersion with different concentrations (1% w/w, 2% w/w, 3% w/w). The prepared mixture was kept in a water bath for 1 h at 25 °C. The turbidity was determined by measuring absorbance at 640 nm against a water blank. 2.8 Freeze-thaw stability Freeze-thaw stability was according to Hoover and Senanayake [22] with some modifications. The NS (1% w/w), PS slurry (1% w/w), N-GCWS (1%w/w) and P-GCWS (1%w/w) were prepared 7
Journal Pre-proof constituents in Turbidity measurements. In a typical experiment, the aqueous starch (40 g) was placed in a 50 mL centrifugal tube. The tube was stored at -20 °C for 16 h followed by thawing at 30 °C for 8 h in a water bath incubator. Then the tubes were centrifuged at 4000 rpm for 10 min. Remove and weigh the supernatant of the samples. This value was the percentage of water separated to the initial gel weight. This freeze–thaw cycle (FTC) was repeated up to six times. 2.9 Cold water viscosity Cold water viscosity of starches was determined by the method of Luis A. Bello-Pe´rez et al.
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[23]. The native starch (6% w/w), porous starch slurry (6% w/w), GCWS (6% w/w) and P-GCWS (6%
2.10 Determination of oil absorption capacity
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determined using spindle No. 2 and No. 3 at 25 °C.
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w/w) starches were prepared constituents in turbidity measurements. Cold paste viscosity was
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The oil absorption capacity of the samples was determined according to the Sathe and Salunkhe [24] with some modifications. In a typical experiment, 60 mL soybean oil was drop into the starch (4
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g) under vortex mixer. The mixture was placed at room temperature (25℃) for 30 min, and then centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was poured out and the
estimated using eqn. (2)
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mass of the mixture was weighed. The oil absorption capacity of the samples was calculated and
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Oil absorption capacity (g/g) =
𝑚1 −𝑚2 𝑚2
Where, m1 is the weight of starch, m2 is the weight of mixture after centrifuged. 2.11. Statistical analysis
All the analytical determinations were carried out in triplicate. Statistical significance analysis was performed using SPSS 17.0 Statistical Software Program (SPSS Inc., Chicago, United States). Mean values and standard deviations were analyzed and reported by using the Origin Program 8.0 (Origin Lab Company, USA). Duncan's multiple range test was applied to evaluate the difference of the means at a significance level of 95% (P < 0.05).
3. Results and discussion 3.1 Cold water-solubility The cold water-solubility obtained for the samples is shown in Table 1. The addition of alkali 8
Journal Pre-proof and ethanol had a great influence on CWS of N-GCWS and P-GCWS starches. N-GCWS and P-GCWS starches with different CWS were prepared by different addition of alkali and ethanol. When starch was in contact with a high concentration of alkali, H3O+ was formed in the starch through OH- in the strong base combined with a specific site of the starch [25], the hydrogen bond and double helix structure inside the starch were destroyed, which causing swell of starch granules [26]. Therefore, as the amount of alkali increased, the CWS of starch was greatly improved. The presence of alcohol not only restricted swelling of starch granules by decreasing the effective water concentration but also acted as a complexing agent to stabilize the dissociated starch chains [13]. In
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the similar CWS, the preparation of P-GCWS starches required less alkali than the preparation of
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N-GCWS. This likely due to the specific surface area of the porous starch was larger than that of the native starch [27], and the contact area of the porous starch with the reactant was greatly increased,
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so the reaction efficiency was improved. The results showed PS was easier to prepare P-GCWS
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starches than WS.
60%N-GCWS
90%N-GCWS
30%P-GCWS
60%P-GCWS
90%P-GCWS
NaOH
17.5g
20g
20g
12.5g
17.5g
17.5g
Ethanol
45g
45g
42.5g
45g
45g
42.5g
CWS
32.54%
58.88%
90.54%
28.22%
62.18%
92.24%
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30%N-GCWS
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Table. 1 The CWS, sodium hydroxide dosage, ethanol dosage of the N-GCWS and P-GCWS
3.2 Polarized light microscopy
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Fig. 1 The polarized crosses (500×) of starch samples (a) WS, (b) 30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.
The starch particles have birefringence under a polarizing microscope because of starch is alternately stacked with semi-crystalline growth rings and amorphous growth rings. The polarized light microscopy of the samples was shown in Fig.1. WS had many clear polarized crosses. However, after enzymatic hydrolysis, the amounts of polarized crosses were reduced and the clarity was also declined. The polarized crosses of the 30%N-GCWS starches was still existed, but the intensity of 10
Journal Pre-proof the birefringence was much less than WS. The cross-polarized crosses of the 60%N-GCWS and 90%N-GCWS starches were completely disappeared. The crystalline region of starch was composed of double helices which were formed by hydrogen bonds between linear portion of amylopectin and an amylose [28]. The strong base would break the hydrogen bond between the double helices of the starch. Therefore, after the ethanol-alkali treatment, the crystalline region of the starch was destroyed. The polarized cross had a tendency to gradually disappear from the umbilical point with the solubility of N-GCWS starches increased. There a natural B-type crystal in the center of the umbilical point of the starch, and a more stable type A crystal was on the surrounding of the starch
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[29]. In addition, some polarized cross of porous waxy corn starch was disappeared, which due to the
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structural fragmentation of starch caused by excessive enzymatic hydrolysis [30]. There was more polarized cross of the N-GCWS than that of P-GCWS starches. This was mainly because the
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presence of the porous structure affected the polarized cross of the sample.
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3.3 Scanning electron microscopy
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The SEM of the samples was showed in Fig.2. Granules of WS appeared with round and polygonal granular shape, and their surface was smooth with some hollows. After enzymatically
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treated, the granular shape of PS was also round and polygonal. However, there were many porous in the surface of PS and the surface became rough. These structural properties were contributed to
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offering a large specific surface area for PS. N-GCWS granules treatment by ethanol-alkali had a dimple in the middle, likely due to starch shrinkage after swelling during treatment. 30% N-GCWS starches preserved their granular structure but their size increased dramatically and had wrinkled surface. This result in agreement with the finding of [10]. As the increased of CWS, surface of N-GCWS granules became more and more shriveled and the granules became completely deformed. The SEM of PS was showed in Fig.2e. After treatment by the ethanol-alkali, hollows were showed in P-GCWS granules, and as the GWS increased, P-GCWS granules became shriveled and completely deformed. It was shown from the Fig.2, under the similar GWS, P-GCWS granules had be more shriveled than N-GCWS granules. Porous were also appeared on the surface of P-GCWS granules. However, as CWS increased, the pores on the surface of P-GCWS starches gradually decreased. This result indicated that the ethanol-alkali treatment would influence but not completely destroy the pores on the surface of PS. These pores increased the specific surface area of P-GCWS starches, 11
Journal Pre-proof which was beneficial to the adsorption of oil by P-GCWS starches. The interaction of the alcohol and the alkali caused the starch to swelling but retained the granular morphology. During drying, the water inside P-GCWS starches was evaporated to form deformed and twisted granule. The morphology of P-GCWS granules with high CWS tended to be flat. It may be caused by excessive
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alkali which will cause the starch granules to break and flat [31].
Fig.2. Scanning electron microphotograph (30000×) of starch samples (a) WS, (b) 30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.
3.4 X-ray diffraction pattern Starches with relatively short average branch lengths (dp23-29), such as waxy corn, corn, rice, wheat, taro, cassava and sweet potato, exhibit type A X-ray diffraction pattern [32]. The X-ray 12
Journal Pre-proof diffraction pattern of different CWS of N-GCWS and P-GCWS was shown in Fig.3 (A). WS and PS exhibited strong reflections at 2θ = 13.05, 23.07, 17.99 and 22.95, which was A-type pattern. N-GCWS and P-GCWS starches treated by ethanol-alkali showed amorphous crystal form. Chen et al. [13] studied the properties of corn starch with different amylose content after ethanol-alkali treatment. It showed that X-ray diffraction pattern of the corn starch and high linear corn starch were changed to V-type by ethanol-alkali treatment. However, WS was changed to an amorphous diffraction peak after being treated by ethanol-alkali. Zhang et al. [16] treated starch alcohol solution at high temperature to obtain GCWS starches. It was found that WS showed amorphous crystal form
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without gelatinization, while corn starch and potato starch were converted into V Type, indicating
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that amylose was very important for the conversion of starch crystal form. Jane et al. [8] proposed that V-complex was formed by amylopectin and amylose combined with alcohol after the starch
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double helix structure was dissociated by heating. When ethanol was removed from the V-complex,
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starch was in a metastable state and can be dissolved in cold water. The amylopectin content of waxy
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corn starch in this work was more than 98%, therefore X-ray diffraction patterns of N-GCWS and P-GCWS starches were shown as amorphous crystal forms. As showed in Fig.3, as CWS increased,
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the peak height of this "Taro Peak" was decreasing because of the action of alkali on starch.
Fig. 3 A: X-ray diffractogram of (a)WS, (b)30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS. B: Turbidimetric of (a)WS, (b)30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS. 3.5 Turbidimetric analysis The turbidity of the samples was presented in Fig.3 (B). The initial turbidity of WS was low and 13
Journal Pre-proof increased rapidly with storage time, indicating that the stability of WS paste was poor. The initial turbidity of N-GCWS starches was higher than that of WS, and the initial turbidity decreased slowly with the increase of GWS. Moreover, N-GCWS starches had good turbidity stability, and storage time had little effect on its turbidity. The initial turbidity of PS was smaller than that of WS, but the stability was higher than that of WS. The initial turbidity of P-GCWS starches was higher than that of PS, and the initial turbidity gradually decreased with the increase of GWS. Therefore, 30% P-GCWS had the highest turbidity; PS had the smallest turbidity; which indicating that the ethanol-alkali process had a great influence on the turbidity of waxy porous corn starch.
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Turbidity effects had their origin in refractive index fluctuation over a distance scale
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comparable to the wavelength of observation. In a polymer-solvent system this was caused by density fluctuations over the same distance scale and was most likely due to extensive
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polymer-polymer aggregation [33]. The change of starch turbidity was caused by starch aging, and
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the aging of starch was affected by the molecular weight, concentration, temperature and non-starch
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components (salts, sugars, lipids, acids, hydrocolloids, surfactants) of starch [34, 35]. The aging of the starch paste was also affected by the molecular chain length in the starch hydrolysate, and the
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longer the chain length, the faster the aging rate [36]. The turbidity of starch increased with the increase of the molecular weight of starch, and the molecular weight of PS was reduced after
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enzymatic hydrolysis, so its initial turbidity was lower than that of WS. The alpha-amylase could hydrolyze alpha-1.4 glycosidic linkages in the starch molecule. Glucose amylase, also known as glucoamylase, can hydrolyze starch from the non-reducing end to produce α-1.4 glucose oxime bond to produce glucose. After enzymatic hydrolysis, the chain length of PS was lower than that of waxy corn. Therefore, the aging rate was slowed down and the turbidity changed slowly. In addition, the turbidity of N-SGWC and P-SGWC starches was higher than that of WS and PS, which was most likely due to the ethanol-alkali treatment to change the starch from a double helix to a single helix, so that water penetrated into the interior of the particle to swell and the amylopectin molecule was dissolved [37]. 3.6 Freeze-thaw stability
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Journal Pre-proof Frozen ready-to eat food products are convenient to use since they require less time to prepare than raw food. However, when this frozen food is thawed for consumption, the moisture readily separates from the matrix and causes a change in the texture, drip loss, and often deterioration in the overall quality [38]. Some modified starch can be used as a food additive to improve the freeze-thaw
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starch [10, 39].
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stability of starch. Studies have shown that GCWS starches can improve the freeze-thaw stability of
Fig.4. Freeze-thaw stability of (a)WS, (b)30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f)
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30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.
The results of the freeze-thaw stability of N-GCWS starches with different CWS were shown in Fig.4. It was shown from the Fig.4. that the freeze-thaw stability of the WS was higher than PS, and the freeze-thaw stability of WS and PS starch was improved after ethanol-alkali treatment. As the CWS increased, the freeze-thaw stability gradually decreased. The WS particles were broken after the gelatinization, but N-GCWS starches still maintained the granular, and the outer wall of the particle had good toughness and strong water retention, so the freeze-thaw stability of N-GCWS starches was better. With the increased of the CWS, the freeze-thaw stability of starch was deteriorated. It was probably due to the presence of starch granules in the N-GCWS starch that were not completely swollen, which inhibited the aging of starch [13], so the freeze-thaw stability was improved. The lower CWS, the more particles that were not completely swollen, so as the CWS increased, the freeze-thaw stability of the N-GCWS decreased. 15
Journal Pre-proof 3.7 Cold paste viscosity The cold paste viscosity of the starches was shown in Fig.5 (A). It shown from the Fig.5, the cold paste viscosity of the PS was lower than that of the WS. After the ethanol-alkali treatment, the cold paste viscosity of the WS and PS increased, and as CWS increased, the cold paste viscosity of
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Fig.5. A: Cold paste viscosity of (a)WS, (b)30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.B: Oil absorption capacity of (a)WS, (b)30%N-GCWS, (c)
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60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.
The cold paste viscosity of N-GCWS starches was higher than that of WS, and this result was
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consistent with the results of Bello-Pérez et al. and Lee et al. [13, 40]. This may be due to the changes in the molecular structure of starch. It was well known that the starch would completely lose its crystalline structure after being heated and gelatinized, and the higher the temperature, the lower the viscosity. Therefore, the cold paste viscosity of WS after the heat treated was the lowest in all the samples. The viscosity was also related to the molecular weight. After treatment by enzyme, the molecular weight of the corn starch became small, so the cold paste viscosity of the PS was lower than that of the WS, and the cold paste viscosity of P-GCWS starches was also lower than that of N-GCWS starches 3.8 Oil absorption capacity The oil absorption capacity of samples was shown in Fig.5 (B). It can be seen from Fig.5 (B) that the oil absorption capacity of N-GCWS starch was higher than that of WS. As CWS increased, 16
Journal Pre-proof the oil absorption capacity of starch was decreased. Under the same CWS, P-GCWS starches had a higher oil absorption capacity than that of N-GCWS. Studies have shown that N-GCWS starches also had the ability to adsorb substances [15]. The oil absorption capacity of N-GCWS starches as higher than that of waxy corn starch, and the oil absorption capacity of P-GCWS starches was higher than that of porous waxy corn starch. This may be related to the swelling of starch after alkali treatment which increased the surface area of starch and increased the area of contact with oil. As the CWS increased, the oil absorption capacity of N-GCWS and P-GCWS starches was gradually decreased. This may be as CWS increased, the surface changes from expansion to flat structure, and
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the surface area decreases, so the oil absorption capacity decreased. In addition, after enzymatic
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hydrolysis, the oil absorption capacity of the starch was increased, and oil absorption capacity of P-GCWS starches was also higher than that of the N-GCWS, which because the pores were formed
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and the adsorption capacity was improved.
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4. Conclusions
The properties of granular cold-water soluble waxy corn starch (N-GCWS) and granular cold-
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water soluble porous waxy corn starch (P-GCWS) were systematically investigated in this work. P-GCWS starches were obtained from PS treated by ethanol-alkali. After alcohol-alkali treatment,
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the polarized crosses of P-GCWS starches and N-GCWS starches would gradually disappear with the increase of CWS. There were many porous in P-GCWS, but as CWS increased, the pores on the surface of the P-GCWS starches gradually decreased. Which means ethanol-alkali treatment would influence but not completely destroy the pores on the surface of the PS. After alcohol-alkali treatment, the X-ray diffraction pattern of the PS and WS changed from A type to amorphous. The N-GCWS and P-GCWS were shown lower initial turbidity, but higher turbidity stability than that of the WS and PS. Cold paste viscosity, freeze-thaw stability and oil absorption capacity of N-GCWS and P-GCWS starches was higher than that of the WS and PS. Moreover, under the similar CWS, P-GCWS starches had a higher oil absorption capacity than that of N-GCWS starches. P-GCWS starches had better water solubility than PS, and had a larger specific surface area and adsorption capacity than N-GCWS starches. Therefore, P-GWSC starches prepared in this paper has great potential in encapsulate various functional items in beverages and water-soluble drugs. Conflict-of-interest statement 17
Journal Pre-proof No conflict of interest exists in the submission of this manuscript, and the manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and is not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is enclosed.
Acknowledge The authors gratefully acknowledge financial support from the National Natural Science Foundation
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of China (Grant No.31230057).
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[31] M.N. Nadiha, A. Fazilah, R. Bhat, A.A. Karim, Comparative susceptibilities of sago, potato and corn starches to alkali treatment, Food Chem. 121(4) (2010) 1053-1059. [32] J.-l. Jane, K.-s. Wong, A.E. McPherson, Branch-structure difference in starches of A-and B-type X-ray patterns revealed by their Naegeli dextrins, Carbohydr. Res. 300(3) (1997) 219-227. [33] Gidley, M. J., Molecular mechanisms underlying amylose aggregation and gelation, Macromolecules 22(1) (1989) 351-358. [34] K.S. Sandhu, N. Singh, Some properties of corn starches II: Physicochemical, gelatinization, retrogradation, pasting and gel textural properties, Food Chem. 101(4) (2007) 1499-1507. [35] E. Durán, A. León, B. Barber, C.B. de Barber, Effect of low molecular weight dextrins on gelatinization and retrogradation of starch, Eur. Food Res. Technol. 212(2) (2001) 203-207. [36] A. Smits, P. Kruiskamp, J. Van Soest, J. Vliegenthart, The influence of various small plasticisers and malto-oligosaccharides on the retrogradation of (partly) gelatinised starch, Carbohydr. Polym. 51(4) (2003) 417-424. 19
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Yun Chen, Guifang Dai, Qunyu Gao PII:
S0141-8130(19)39367-5
DOI:
https://doi.org/10.1016/j.ijbiomac.2019.12.060
Reference:
BIOMAC 14087
To appear in:
International Journal of Biological Macromolecules
Received date:
17 November 2019
Revised date:
2 December 2019
Accepted date:
7 December 2019
Please cite this article as: Y. Chen, G. Dai and Q. Gao, Preparation and properties of granular cold-water-soluble porous starch, International Journal of Biological Macromolecules(2019), https://doi.org/10.1016/j.ijbiomac.2019.12.060
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Journal Pre-proof
Preparation and properties of granular cold-water-soluble porous starch Yun Chen, Guifang Dai, Qunyu Gao* Carbohydrate Laboratory, School of Food Science and Engineering, South China University of Technology, No. 381, Wushan Road, Guangzhou 510640, China
*
Corresponding author. Tel: +86-13660261703; Fax: +86-20-87113848
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Email: [email protected], [email protected]
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Journal Pre-proof Highlights 1. Granular cold-water soluble porous starch was prepared from porous waxy corn starch 2. PS was easier to prepare P-GCWS than WS prepared N-GCWS 3. The surface area of P-GCWS was higher than that of N-GCWS
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4. The oil absorption capacity of P-GCWS was higher than that of N-GCWS
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Journal Pre-proof Abstract: In this work, granular cold-water soluble waxy corn starch (N-GCWS) and granular coldwater soluble porous waxy corn starch (P-GCWS) were prepared by waxy corn starch (WS) treated with alcohol-alkali. Starch morphologies, crystal structures, turbidity, cold water viscosity, freeze-thaw stability and oil absorption capacity of N-GCWS and P-GCWS starches were compared. The results showed porous waxy corn starch (PS) was easier to prepare P-GCWS starch than WS to prepare N-GCWS. SEM showed that PS and WS became dent-twisted and tended to flatten with the increase of CWS. After alcohol-alkali treatment, the X-ray diffraction pattern of PS and WS changed from A type to amorphous and pores were remained on the surface of P-GCWS starches granular.
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Turbidity, freeze-thaw stability, viscosity, oil absorption capacity of N-GCWS and P-GCWS starches
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was shown higher than that of WS and PS. The oil absorption capacity of P-GCWS was higher than
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that of N-GCWS.
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Keywords: waxy corn starch, porous starch, granular cold-water soluble starch, absorption capacity
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Introduction Starch is the most important carbohydrate which widely used in the human nutrition and industry such as gelling agent, thickening agent, bulking agent, stabilizer and Pickering emulsions [1-3]. Although starch is hydrophilic because it contains a large amount of hydroxyl groups, the native starch is water insoluble at room temperature thus native starch cannot play as thickener, gelling agent and water binder. Therefore, many studies have been focused on the development of starch denaturation and its derivatives. Cold-water-soluble starches, such as pregelatinized starches
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which would absorb water and promote viscosity at room temperature, are being developed to broaden the application of starch [4, 5]. Drum drying and extrusion are often used to prepare
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pregelatinized starches [6, 7]. However, the pregelatinized starches made by drum drying show
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rough and poor flexibility which not match the quality of instant foods. Granular cold-water soluble (GCWS) starches are also one of the cold-water-soluble starches. Compared with the pregelatinized
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starches, GCWS starches give higher viscosity and smoother texture.
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Jane et al. [8] described a process for preparing GCWS starches using aqueous alcohol treatment at high temperature. Dries ed al [9] treated the maize starch starches with aqueous ethanol
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treatments at elevated temperatures and atmospheric pressure to prepare GCWS starches and found that ethanol concentrations had great influence on the preparation of the GCWS starches. The
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ethanol-alkali method is widely used to preparing GCWS starches, because it can be used to various native starch to prepare GCWS starches at ambient temperature and pressure [10, 11]. The hydroxyl group on the starch molecule has a negative charge in the strong alkali environment. When the concentration of the alkali solution is gradually increased, more and more negatively charged hydroxyl bands cause the hydrogen bond between the starch molecules to break, and double helical of the starches becomes a single helix [12]. The presence of alcohol not only restricts swelling of starch granules by decreasing the effective water concentration but also acts as a complexing agent to stabilize the dissociated starch chains [13]. During the drying process, the volatilization of ethanol causes a cavity to form inside the starch, then GCWS starches have intact particles and good solubility. GCWS starches can be used in many food products as thickening agents. Moreover, GCWS starches can also be used to encapsulating materials, such as encapsulation of ethylene gas [14] and encapsulation of atrazine [15]. 4
Journal Pre-proof Porous starch has abundant micro-sized pores from the surface extending to the center. The porous starch exhibits a "sponge" structure which allows the starch to have a large specific surface area and specific pore volume, so the adsorption capacity is greater than that of the native starch [16]. Substance can easily adhere firmly to the inner wall of the porous starch, moreover some substances that are unstable to temperature, light and oxygen can be protected by porous starch. Therefore, porous starch can be used as an adsorbent in many areas such as food, medicine, chemical industry and agriculture. Zhang ed. al [16] had been used the porous corn starch which prepared by α-amylase and glucoamylase hydrolysis as adsorbent adsorbing methyl violet. Glen ed al [17] described that
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porous starch microspheres prepared from high-amylose corn starch encapsulate essential plant oils
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and yet remain an easily dispersed powder. Porous starch can also encapsulate grape seed proanthocyanidins and Lactobacillus plantarum [18, 19].
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Here, P-GCWS starches were prepared from porous waxy corn starch by ethanol-alkali
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treatment. To the best of our knowledge, this is the first report on the preparation and properties of
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P-GCWS starches. After treated by alcohol-alkali, not only the encapsulation but also the water solubility of the porous starch would be significantly improved. Thereby the range of porous starch
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in the food industry would be significant expanded. Starch morphologies, crystal structures, turbidity, freeze-thaw stability, cold water viscosity and oil absorption capacity of N-GCWS and P-GCWS
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starches were comparative studied in this work. The results show that after treated by alcohol-alkali, there were still many porous in the surface of the porous starch granules. PS was easier to prepare P-GCWS starches than WS because of higher surface area. Oil absorption capacity of P-GCWS starches was higher than that of N-GCWS starches. This means the large specific surface area and excellent encapsulation of porous starch can be maintained after alcohol-alkali treatment.
2 Materials and methods 2.1 Materials Waxy corn starch was donated by Qinhuangdao Lihua Starch Co., Ltd, China. Amyloglucosidase (23 units/mg) and α-amylase (16 units/mg) were purchased from Sigma-Aldrich Chemical Company, USA. Absolute ethanol, hydrochloric acid and sodium hydroxide were sought from Guangzhou Chemical Reagent Factory. Sodium acetate and glacial acetic acid were purchased from Shanghai Runjie Chemical Reagent Co., Ltd. Chemicals and solvents used in this work were 5
Journal Pre-proof analytical grade. 2.2 Preparation of N-GCWS and P-GCWS The waxy maize porous starch were prepared according to Zhang [16] with some modifications. Briefly, waxy maize starch suspensions (100 g, 30%) were prepared with sodium acetate buffer (pH=5.5). The suspensions were kept under 100 rpm mechanical stirring at 50 °C for 1h, then 1.5g mixed enzyme (α-amylase: amyloglucosidase = 3:1) was added to the suspensions. After 12 h of reaction at 50 °C, the solution was adjusted to pH = 10 with NaOH (1 M) solution. The suspensions
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were washed by successive centrifugation with distilled water to pH nearly 7. The N-GCWS and P-GCWS starch were prepared according to Chen et al.[15]. Typically,
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waxy maize starch (5g, dry weight basis) suspensions and porous starch (5g, dry weight basis)
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suspensions were prepared with absolute ethanol. After the prepared suspension was placed in a 25 ° C water bath and stirred uniformly, sodium hydroxide solution (3M) was added slowly to the
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suspensions (4 mL/min). After the required NaOH was added, continue stirring for a certain period
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of time, then pour out the supernatant. 80% ethanol solution was added to the sample and the pH was adjusted to neutral with hydrochloric acid solution. The sample was washed with anhydrous ethanol
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several times. 2.3 Cold water solubility
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The method of determined cold water solubility (CWS) was according to Eastman and Moore [20] with some modification. Typical, 100 mL distilled water was added to a bender beaker. The starch samples were added into the blender operated at a low speed (500 rpm) for 30 s. Then the blender was switched to a high speed (1000rpm) for 2 min. The starch suspension was transferred to a centrifuge cup and centrifuge at 3100 rpm for 15 min. 25 mL aliquot of the supernatant was transferred to a tared petri dish and dried in an oven at 120℃ to constant weight. The CWS was calculated by eqn. (1): CWS(%) =
grams of solids in supernatant×4 grams of samples
× 100%
(1)
2.4 Polarized light microscopy Native and GCWS starch suspensions (water-glycerol 50:50 v/v) were observed under crossed polarized light (magnification 200×) using a binocular microscope (Eclipse 80i, Nikon Inc., Melville, 6
Journal Pre-proof NY, USA) equipped with real time viewing (Q-capture Pro, Q-Imaging, BC, Japan). A Q-Imaging digital camera (QICAM fast 1394, BC, Japan) was used for image capture. 2.5 Scanning Electron Microscopy (SEM) Scanning electron microscopy (SEM) was used to analyze the micro-morphology of native and modified maize starch. Starch samples were scattered on double-sided adhesive tape attached to a circular aluminum stub, and coated with 20 NS gold under vacuum. After then, the samples were viewed and photographed with a scanning electron microscope (model EVO 18, Zeiss, Germany) at
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an acceleration potential of 20 kV.
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2.6 X-ray diffraction (XRD) pattern
The samples were first placed in a dryer at a relative humidity of 15% for 24 h to ensure that all
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samples had the same moisture content. The X-ray diffraction (XRD) patterns of different samples
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were obtained with a D/Max-2200 X-ray diffraction (Rigaku Denki Co., Tokyo, Japan) using Cu Kα radiation at 44 kV and 26 mA. The diffraction angle ranged from 4° to 40° (2θ) at the rate of 5°/min
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(Yanika, Chureerat, Vilai, & Dudsadee, 2009). Relative crystallinity was calculated based on the
Komiya, 1983).
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2.7 Turbidity measurements
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method described by the ratio of crystalline area to total diffractogram area (Nara, Sakakura, &
The measurement of turbidity was according to Perera et al. [21]. The native starch and porous starch were added to water to prepare starch suspensions with different concentrations (1% w/w, 2% w/w, 3% w/w), and the mixture was heated in a boiling water bath for 30 minutes under constant stirring. N-GCWS and P-GCWS starches was slowly added to distilled water under low-speed stirring for 10min, and then stirred under high-speed stirring for 20 min to dissolve in water to prepare starch dispersion with different concentrations (1% w/w, 2% w/w, 3% w/w). The prepared mixture was kept in a water bath for 1 h at 25 °C. The turbidity was determined by measuring absorbance at 640 nm against a water blank. 2.8 Freeze-thaw stability Freeze-thaw stability was according to Hoover and Senanayake [22] with some modifications. The NS (1% w/w), PS slurry (1% w/w), N-GCWS (1%w/w) and P-GCWS (1%w/w) were prepared 7
Journal Pre-proof constituents in Turbidity measurements. In a typical experiment, the aqueous starch (40 g) was placed in a 50 mL centrifugal tube. The tube was stored at -20 °C for 16 h followed by thawing at 30 °C for 8 h in a water bath incubator. Then the tubes were centrifuged at 4000 rpm for 10 min. Remove and weigh the supernatant of the samples. This value was the percentage of water separated to the initial gel weight. This freeze–thaw cycle (FTC) was repeated up to six times. 2.9 Cold water viscosity Cold water viscosity of starches was determined by the method of Luis A. Bello-Pe´rez et al.
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[23]. The native starch (6% w/w), porous starch slurry (6% w/w), GCWS (6% w/w) and P-GCWS (6%
2.10 Determination of oil absorption capacity
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determined using spindle No. 2 and No. 3 at 25 °C.
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w/w) starches were prepared constituents in turbidity measurements. Cold paste viscosity was
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The oil absorption capacity of the samples was determined according to the Sathe and Salunkhe [24] with some modifications. In a typical experiment, 60 mL soybean oil was drop into the starch (4
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g) under vortex mixer. The mixture was placed at room temperature (25℃) for 30 min, and then centrifuged at 5000 rpm for 10 min. After centrifugation, the supernatant was poured out and the
estimated using eqn. (2)
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mass of the mixture was weighed. The oil absorption capacity of the samples was calculated and
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Oil absorption capacity (g/g) =
𝑚1 −𝑚2 𝑚2
Where, m1 is the weight of starch, m2 is the weight of mixture after centrifuged. 2.11. Statistical analysis
All the analytical determinations were carried out in triplicate. Statistical significance analysis was performed using SPSS 17.0 Statistical Software Program (SPSS Inc., Chicago, United States). Mean values and standard deviations were analyzed and reported by using the Origin Program 8.0 (Origin Lab Company, USA). Duncan's multiple range test was applied to evaluate the difference of the means at a significance level of 95% (P < 0.05).
3. Results and discussion 3.1 Cold water-solubility The cold water-solubility obtained for the samples is shown in Table 1. The addition of alkali 8
Journal Pre-proof and ethanol had a great influence on CWS of N-GCWS and P-GCWS starches. N-GCWS and P-GCWS starches with different CWS were prepared by different addition of alkali and ethanol. When starch was in contact with a high concentration of alkali, H3O+ was formed in the starch through OH- in the strong base combined with a specific site of the starch [25], the hydrogen bond and double helix structure inside the starch were destroyed, which causing swell of starch granules [26]. Therefore, as the amount of alkali increased, the CWS of starch was greatly improved. The presence of alcohol not only restricted swelling of starch granules by decreasing the effective water concentration but also acted as a complexing agent to stabilize the dissociated starch chains [13]. In
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the similar CWS, the preparation of P-GCWS starches required less alkali than the preparation of
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N-GCWS. This likely due to the specific surface area of the porous starch was larger than that of the native starch [27], and the contact area of the porous starch with the reactant was greatly increased,
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so the reaction efficiency was improved. The results showed PS was easier to prepare P-GCWS
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starches than WS.
60%N-GCWS
90%N-GCWS
30%P-GCWS
60%P-GCWS
90%P-GCWS
NaOH
17.5g
20g
20g
12.5g
17.5g
17.5g
Ethanol
45g
45g
42.5g
45g
45g
42.5g
CWS
32.54%
58.88%
90.54%
28.22%
62.18%
92.24%
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30%N-GCWS
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Table. 1 The CWS, sodium hydroxide dosage, ethanol dosage of the N-GCWS and P-GCWS
3.2 Polarized light microscopy
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Fig. 1 The polarized crosses (500×) of starch samples (a) WS, (b) 30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.
The starch particles have birefringence under a polarizing microscope because of starch is alternately stacked with semi-crystalline growth rings and amorphous growth rings. The polarized light microscopy of the samples was shown in Fig.1. WS had many clear polarized crosses. However, after enzymatic hydrolysis, the amounts of polarized crosses were reduced and the clarity was also declined. The polarized crosses of the 30%N-GCWS starches was still existed, but the intensity of 10
Journal Pre-proof the birefringence was much less than WS. The cross-polarized crosses of the 60%N-GCWS and 90%N-GCWS starches were completely disappeared. The crystalline region of starch was composed of double helices which were formed by hydrogen bonds between linear portion of amylopectin and an amylose [28]. The strong base would break the hydrogen bond between the double helices of the starch. Therefore, after the ethanol-alkali treatment, the crystalline region of the starch was destroyed. The polarized cross had a tendency to gradually disappear from the umbilical point with the solubility of N-GCWS starches increased. There a natural B-type crystal in the center of the umbilical point of the starch, and a more stable type A crystal was on the surrounding of the starch
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[29]. In addition, some polarized cross of porous waxy corn starch was disappeared, which due to the
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structural fragmentation of starch caused by excessive enzymatic hydrolysis [30]. There was more polarized cross of the N-GCWS than that of P-GCWS starches. This was mainly because the
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presence of the porous structure affected the polarized cross of the sample.
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3.3 Scanning electron microscopy
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The SEM of the samples was showed in Fig.2. Granules of WS appeared with round and polygonal granular shape, and their surface was smooth with some hollows. After enzymatically
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treated, the granular shape of PS was also round and polygonal. However, there were many porous in the surface of PS and the surface became rough. These structural properties were contributed to
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offering a large specific surface area for PS. N-GCWS granules treatment by ethanol-alkali had a dimple in the middle, likely due to starch shrinkage after swelling during treatment. 30% N-GCWS starches preserved their granular structure but their size increased dramatically and had wrinkled surface. This result in agreement with the finding of [10]. As the increased of CWS, surface of N-GCWS granules became more and more shriveled and the granules became completely deformed. The SEM of PS was showed in Fig.2e. After treatment by the ethanol-alkali, hollows were showed in P-GCWS granules, and as the GWS increased, P-GCWS granules became shriveled and completely deformed. It was shown from the Fig.2, under the similar GWS, P-GCWS granules had be more shriveled than N-GCWS granules. Porous were also appeared on the surface of P-GCWS granules. However, as CWS increased, the pores on the surface of P-GCWS starches gradually decreased. This result indicated that the ethanol-alkali treatment would influence but not completely destroy the pores on the surface of PS. These pores increased the specific surface area of P-GCWS starches, 11
Journal Pre-proof which was beneficial to the adsorption of oil by P-GCWS starches. The interaction of the alcohol and the alkali caused the starch to swelling but retained the granular morphology. During drying, the water inside P-GCWS starches was evaporated to form deformed and twisted granule. The morphology of P-GCWS granules with high CWS tended to be flat. It may be caused by excessive
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alkali which will cause the starch granules to break and flat [31].
Fig.2. Scanning electron microphotograph (30000×) of starch samples (a) WS, (b) 30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.
3.4 X-ray diffraction pattern Starches with relatively short average branch lengths (dp23-29), such as waxy corn, corn, rice, wheat, taro, cassava and sweet potato, exhibit type A X-ray diffraction pattern [32]. The X-ray 12
Journal Pre-proof diffraction pattern of different CWS of N-GCWS and P-GCWS was shown in Fig.3 (A). WS and PS exhibited strong reflections at 2θ = 13.05, 23.07, 17.99 and 22.95, which was A-type pattern. N-GCWS and P-GCWS starches treated by ethanol-alkali showed amorphous crystal form. Chen et al. [13] studied the properties of corn starch with different amylose content after ethanol-alkali treatment. It showed that X-ray diffraction pattern of the corn starch and high linear corn starch were changed to V-type by ethanol-alkali treatment. However, WS was changed to an amorphous diffraction peak after being treated by ethanol-alkali. Zhang et al. [16] treated starch alcohol solution at high temperature to obtain GCWS starches. It was found that WS showed amorphous crystal form
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without gelatinization, while corn starch and potato starch were converted into V Type, indicating
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that amylose was very important for the conversion of starch crystal form. Jane et al. [8] proposed that V-complex was formed by amylopectin and amylose combined with alcohol after the starch
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double helix structure was dissociated by heating. When ethanol was removed from the V-complex,
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starch was in a metastable state and can be dissolved in cold water. The amylopectin content of waxy
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corn starch in this work was more than 98%, therefore X-ray diffraction patterns of N-GCWS and P-GCWS starches were shown as amorphous crystal forms. As showed in Fig.3, as CWS increased,
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the peak height of this "Taro Peak" was decreasing because of the action of alkali on starch.
Fig. 3 A: X-ray diffractogram of (a)WS, (b)30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS. B: Turbidimetric of (a)WS, (b)30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS. 3.5 Turbidimetric analysis The turbidity of the samples was presented in Fig.3 (B). The initial turbidity of WS was low and 13
Journal Pre-proof increased rapidly with storage time, indicating that the stability of WS paste was poor. The initial turbidity of N-GCWS starches was higher than that of WS, and the initial turbidity decreased slowly with the increase of GWS. Moreover, N-GCWS starches had good turbidity stability, and storage time had little effect on its turbidity. The initial turbidity of PS was smaller than that of WS, but the stability was higher than that of WS. The initial turbidity of P-GCWS starches was higher than that of PS, and the initial turbidity gradually decreased with the increase of GWS. Therefore, 30% P-GCWS had the highest turbidity; PS had the smallest turbidity; which indicating that the ethanol-alkali process had a great influence on the turbidity of waxy porous corn starch.
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Turbidity effects had their origin in refractive index fluctuation over a distance scale
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comparable to the wavelength of observation. In a polymer-solvent system this was caused by density fluctuations over the same distance scale and was most likely due to extensive
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polymer-polymer aggregation [33]. The change of starch turbidity was caused by starch aging, and
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the aging of starch was affected by the molecular weight, concentration, temperature and non-starch
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components (salts, sugars, lipids, acids, hydrocolloids, surfactants) of starch [34, 35]. The aging of the starch paste was also affected by the molecular chain length in the starch hydrolysate, and the
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longer the chain length, the faster the aging rate [36]. The turbidity of starch increased with the increase of the molecular weight of starch, and the molecular weight of PS was reduced after
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enzymatic hydrolysis, so its initial turbidity was lower than that of WS. The alpha-amylase could hydrolyze alpha-1.4 glycosidic linkages in the starch molecule. Glucose amylase, also known as glucoamylase, can hydrolyze starch from the non-reducing end to produce α-1.4 glucose oxime bond to produce glucose. After enzymatic hydrolysis, the chain length of PS was lower than that of waxy corn. Therefore, the aging rate was slowed down and the turbidity changed slowly. In addition, the turbidity of N-SGWC and P-SGWC starches was higher than that of WS and PS, which was most likely due to the ethanol-alkali treatment to change the starch from a double helix to a single helix, so that water penetrated into the interior of the particle to swell and the amylopectin molecule was dissolved [37]. 3.6 Freeze-thaw stability
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Journal Pre-proof Frozen ready-to eat food products are convenient to use since they require less time to prepare than raw food. However, when this frozen food is thawed for consumption, the moisture readily separates from the matrix and causes a change in the texture, drip loss, and often deterioration in the overall quality [38]. Some modified starch can be used as a food additive to improve the freeze-thaw
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starch [10, 39].
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stability of starch. Studies have shown that GCWS starches can improve the freeze-thaw stability of
Fig.4. Freeze-thaw stability of (a)WS, (b)30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f)
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30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.
The results of the freeze-thaw stability of N-GCWS starches with different CWS were shown in Fig.4. It was shown from the Fig.4. that the freeze-thaw stability of the WS was higher than PS, and the freeze-thaw stability of WS and PS starch was improved after ethanol-alkali treatment. As the CWS increased, the freeze-thaw stability gradually decreased. The WS particles were broken after the gelatinization, but N-GCWS starches still maintained the granular, and the outer wall of the particle had good toughness and strong water retention, so the freeze-thaw stability of N-GCWS starches was better. With the increased of the CWS, the freeze-thaw stability of starch was deteriorated. It was probably due to the presence of starch granules in the N-GCWS starch that were not completely swollen, which inhibited the aging of starch [13], so the freeze-thaw stability was improved. The lower CWS, the more particles that were not completely swollen, so as the CWS increased, the freeze-thaw stability of the N-GCWS decreased. 15
Journal Pre-proof 3.7 Cold paste viscosity The cold paste viscosity of the starches was shown in Fig.5 (A). It shown from the Fig.5, the cold paste viscosity of the PS was lower than that of the WS. After the ethanol-alkali treatment, the cold paste viscosity of the WS and PS increased, and as CWS increased, the cold paste viscosity of
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the starch showed a downward trend.
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Fig.5. A: Cold paste viscosity of (a)WS, (b)30%N-GCWS, (c) 60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.B: Oil absorption capacity of (a)WS, (b)30%N-GCWS, (c)
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60%N-GCWS, (d) 90%N-GCWS, (e) PS, (f) 30%P-GCWS, (g) 60%P-GCWS, (h) 90%P-GCWS.
The cold paste viscosity of N-GCWS starches was higher than that of WS, and this result was
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consistent with the results of Bello-Pérez et al. and Lee et al. [13, 40]. This may be due to the changes in the molecular structure of starch. It was well known that the starch would completely lose its crystalline structure after being heated and gelatinized, and the higher the temperature, the lower the viscosity. Therefore, the cold paste viscosity of WS after the heat treated was the lowest in all the samples. The viscosity was also related to the molecular weight. After treatment by enzyme, the molecular weight of the corn starch became small, so the cold paste viscosity of the PS was lower than that of the WS, and the cold paste viscosity of P-GCWS starches was also lower than that of N-GCWS starches 3.8 Oil absorption capacity The oil absorption capacity of samples was shown in Fig.5 (B). It can be seen from Fig.5 (B) that the oil absorption capacity of N-GCWS starch was higher than that of WS. As CWS increased, 16
Journal Pre-proof the oil absorption capacity of starch was decreased. Under the same CWS, P-GCWS starches had a higher oil absorption capacity than that of N-GCWS. Studies have shown that N-GCWS starches also had the ability to adsorb substances [15]. The oil absorption capacity of N-GCWS starches as higher than that of waxy corn starch, and the oil absorption capacity of P-GCWS starches was higher than that of porous waxy corn starch. This may be related to the swelling of starch after alkali treatment which increased the surface area of starch and increased the area of contact with oil. As the CWS increased, the oil absorption capacity of N-GCWS and P-GCWS starches was gradually decreased. This may be as CWS increased, the surface changes from expansion to flat structure, and
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the surface area decreases, so the oil absorption capacity decreased. In addition, after enzymatic
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hydrolysis, the oil absorption capacity of the starch was increased, and oil absorption capacity of P-GCWS starches was also higher than that of the N-GCWS, which because the pores were formed
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and the adsorption capacity was improved.
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on the starch granules surface after the enzymatic treatment. The specific surface area was increased
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4. Conclusions
The properties of granular cold-water soluble waxy corn starch (N-GCWS) and granular cold-
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water soluble porous waxy corn starch (P-GCWS) were systematically investigated in this work. P-GCWS starches were obtained from PS treated by ethanol-alkali. After alcohol-alkali treatment,
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the polarized crosses of P-GCWS starches and N-GCWS starches would gradually disappear with the increase of CWS. There were many porous in P-GCWS, but as CWS increased, the pores on the surface of the P-GCWS starches gradually decreased. Which means ethanol-alkali treatment would influence but not completely destroy the pores on the surface of the PS. After alcohol-alkali treatment, the X-ray diffraction pattern of the PS and WS changed from A type to amorphous. The N-GCWS and P-GCWS were shown lower initial turbidity, but higher turbidity stability than that of the WS and PS. Cold paste viscosity, freeze-thaw stability and oil absorption capacity of N-GCWS and P-GCWS starches was higher than that of the WS and PS. Moreover, under the similar CWS, P-GCWS starches had a higher oil absorption capacity than that of N-GCWS starches. P-GCWS starches had better water solubility than PS, and had a larger specific surface area and adsorption capacity than N-GCWS starches. Therefore, P-GWSC starches prepared in this paper has great potential in encapsulate various functional items in beverages and water-soluble drugs. Conflict-of-interest statement 17
Journal Pre-proof No conflict of interest exists in the submission of this manuscript, and the manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and is not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is enclosed.
Acknowledge The authors gratefully acknowledge financial support from the National Natural Science Foundation
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of China (Grant No.31230057).
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