The optimization of isoamylase processing conditions for the preparation of high-amylose ginkgo starch

International Journal of Biological Macromolecules 86 (2016) 105–111

Contents lists available at ScienceDirect

International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac

The optimization of isoamylase processing conditions for the preparation of high-amylose ginkgo starch Lanlan Hu a , Yi Zheng a,b , Yujiao Peng a , Cheng Yao a,∗ , Huanxin Zhang b,c,∗ a b c

College of chemistry and molecular engineering, Nanjing Tech University, Nanjing 211816, China Jiangsu Agri-animal Husbandry Vocational College, 8 Fenghuang East Road, Taizhou 225300, China State Key Laboratory of Food Science & Technology, Jiangnan University, Wuxi, Jiangsu 214122, PR China

a r t i c l e

i n f o

Article history: Received 10 November 2015 Received in revised form 4 January 2016 Accepted 12 January 2016 Available online 15 January 2016 Keywords: Gingko starch High-amylose Isoamylase Morphology Thermal properties

a b s t r a c t A high-amylose starch was prepared from ginkgo by hydrolysis using isoamylase and its structures (morphology and crystallinity) and physicochemical properties (swelling factor, water solubility and gelatinization) were determined. The experiments used response surface methodology to determine the optimum parameters for enzymatic hydrolysis: pH 5.0 at 52 ◦ C for 170 min, using an enzyme dose greater than 100 IU/ml. The experimentally observed maximum yield of ginkgo amylose under these conditions was 74.74% and the blue value was 0.756. The high-amylose ginkgo starch showed an irregular surface and porous inner structure while the native starch granules were oval with a smooth surface. X-ray showed that the high-amylose starch displayed a V-type structure. Because of its high amylose content and different structural characteristics, high-amylose starch exhibited a higher gelatinization peak temperature (109.25 ◦ C) and water solubility, and a lower crystallinity (19.13%), gelatinization enthalpy (63.83 J/g), and swelling power. The present study has indicated that high-amylose starch prepared using isoamylase has unique functional properties, which lays the foundation for the wider application of ginkgo starch. © 2016 Published by Elsevier B.V.

1. Introduction Ginkgo is a non-conventional food resource whose seeds contain about 60%–70% starch, 10%–20% protein, 2%–4% lipid and 0.8%–1.2% pectin [1–3]. It has not been widely studied, but its particular functional properties and potential use have attracted more attention in recent years. Ginkgo starch consists of two main components: linear amylose and highly-branched amylopectin. Amylose has mainly linear molecules with ␣-1,4 linked d-glucosyl units and a few branches of ␣-1,6 linkages, whereas amylopectin has large numbers of branch chains which are linked to the linear chains by ␣-1,6 linkages [4–6]. The ratio of amylose to amylopectin contents in starch varies depending on botanical source. Normal starches consist of 20–30% amylose and 70–80% amylopectin, but waxy starches contain almost 100% amylopectin. As for the ginkgo, the apparent amylose content was reported ranging from 26% to 36% [1–3]. The extent of amylose leaching was 4.0–27.2% in ginkgo starch [1]. It has been reported that amylose leaching was influenced by lipid-complexed amylose, total amylose content and

∗ Corresponding authors. Fax: +86 25 5813 9482. E-mail addresses: [email protected] (C. Yao), [email protected] (H. Zhang). http://dx.doi.org/10.1016/j.ijbiomac.2016.01.045 0141-8130/© 2016 Published by Elsevier B.V.

interaction between starch chains [7]. Jane has ever examined the branch chain length distribution of ginkgo. The result showed that the amylopectin had a peak dp number of 13 and chains up to dp number 82. The average chain length for ginkgo is 24.2 [2]. High-amylose starch is of particular interest because its highly retrograded form has been classified as a resistant starch (RS3, the retrograded form) [8]. Amylose retrogradation is a rapid process completed within 48 h, whereas amylopectin retrogradation may continue for several weeks [9]. Because of the structural stability of amylose, some high-amylose cereal crop lines have played an important role in the technology of packaging films, food, medical treatment, textiles, paper making, packaging, petroleum, environmental protection, optical fibers, printed circuit boards, and electronic chips [10–13]. Therefore, great efforts have been made to develop other crops containing high-amylose starch because of its unique functional and nutritional properties. In general, altered amylose is present because of the starch’s botanical origins [14–16], gene mutations or gene silencing [17,18] and enzymatic modification [19]. Enzymatic modification, where branch-chains are removed from amylose, give the resultant chains more opportunities to align and aggregate to form perfectly crystalline structures, which in turn leads to forming more high-amylose starch [20]. It has been reported that a debranching procedure for waxy and low-amylose rice starches used isoamylase, but the relevant

106

L. Hu et al. / International Journal of Biological Macromolecules 86 (2016) 105–111

reactions were not studied [21]. The objective of the present study is therefore to understand the interactions between efficiency as given by amylose yield and the modification factors (enzyme dosage, pH, temperature and reaction time), and also to locate their optimum levels using response surface methodology. Starches will be isolated from mature ginkgo seeds and modified with isoamylase. Their structures (morphology and crystallinity) and physicochemical properties (swelling factor, water solubility and gelatinization) will be investigated using SEM (Scanning Electron Microscopy), X-ray diffraction and DSC (Differential Scanning Calorimetry). 2. Materials and methods 2.1. Materials Mature fruits were collected from trees of Ginkgo biloba cv. Dafozhi located in Taixing County, Jiangsu Province, China. The granular starch debranching enzyme, isoamylase (1000 IU/ml in 0.02% sodium azide) from pseudomonas sp. was obtained from Megazyme International (Bray, Ireland). All other chemicals were reagent grade and obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). 2.2. Starch isolation Ginkgo starch was isolated in the laboratory using the methods reported by Zheng et al. [22]. 2.3. The formation of high-amylose starch Starch was dispersed in phosphate buffer (at pH values of 4.2, 4.6, 5.0, 5.4 and 5.8) and heated at 100 ◦ C for 30 min to form a starch slurry (1% w/w, dry basis). The temperature of the starch slurry was adjusted to 50 ◦ C and other temperatures (42, 46, 54 and 58 ◦ C). The samples were then debranched using isoamylase enzyme at different concentrations (40, 60, 80, 100 and 120 IU/ml of starch slurry) for different periods (1, 2, 3, 4, 5 and 6 h) in a shaking water bath. After the reaction, two volumes of 95% ethanol were added immediately to facilitate the enzyme reaction. The mixture was centrifuged at 2200 × g for 10 min and washed twice with ethanol. The high-amylose samples were dried in an oven at 50 ◦ C for 24 h and then passed through a 100-mesh sieve. 2.4. Starch-iodine absorbance spectra and amylose content The apparent amylose content was determined by an iodine colorimetric method [23] with a slight modification. 10 mg starch was suspended in 1 ml ethanol and 10 ml NaOH (0.1 M). 1 ml of HCl (1 M) was added after the suspension was heated in boiling water for 30 min to make the solution neutral (pH 7.0). The suspension was made up to 50 ml with distilled water after cooling. A 1-ml aliquot of the solution was added to 0.2 ml 0.5% iodine solution and made up to 10 ml with distilled water. The absorbance spectra and the wavelength of maximum absorption (max ) were analyzed over a wavelength range of 500–800 nm. A calibration curve was established using a mixture of amylose and amylopectin from potato starch. 2.5. Granule morphology For the SEM study, the starch granules were mounted on circular aluminum stubs using double-sided adhesive tape and then coated with gold. This was deposited under vacuum with an evaporator in a JSM 6510 electron microscope (JEOL, Tokyo, Japan). All samples were examined using an acceleration voltage of 15 kV, observed in

the microscope and recorded photographically using the method of Lu et al. [24].

2.6. Swelling power and water solubility of starch granules The swelling power and water solubility of the native starch and the modified amylose starch produced by enzymatic hydrolysis using isoamylase were determined according to the method of Karim et al. [25] with a slight modification. Starch (0.5 g) was suspended in 50 ml water and heated in a water bath from 60 to 95 ◦ C in 5 ◦ C steps over 30 min with shaking. The tubes were cooled rapidly to room temperature and then centrifuged at 2200 × g for 20 min. The lipid was removed and dried under vacuum for 2 h at 130 ◦ C to obtain the residue and weighed to calculate the starch solubility. The swelling power was determined by calculating the amount of original precipitate and water absorbed by starch after subtraction of the amount of solubilized starch. Three replicate samples were used in this determination.

2.7. Thermal properties The thermal characteristics of the starches were studied using differential scanning calorimetry (Diamond DSC, PerkinElmer Inc., Waltham, MA, USA) according to the method described by UtrillaCoello et al. [26] with slight modifications. Each sample (3 mg, dry weight) was placed in an aluminum pan and 6 ml of deionized water was added. The samples were hermetically sealed and allowed to stand for 1 h before heating in the DSC. The analysis was carried out by heating the pan from 30 to 150 ◦ C at a rate of 10 ◦ C/min. The DSC analyzer was calibrated using an empty aluminum pan as a reference. The data of the onset (To ), peak (Tp ), end temperatures (Te ) and the gelatinization enthalpy (Hgel ) were obtained using the instrument’s software.

2.8. X-ray diffraction pattern The X-ray diffraction patterns of the starches were obtained using the method of Miao et al. [27] with an X-ray powder diffractometer (Rigaku, Tokyo, Japan) operating at 40 kV and 30 mA. The starch samples were scanned at a rate of 2◦ /min over the diffraction angle (2) from 5 to 35◦ at room temperature. The relative crystallinity was calculated according to the following equation: X c = Ac /(Aa + Ac ) Where Xc is the relative crystallinity, Ac is the crystalline area and Aa is the amorphous area on the X-ray diffractogram.

2.9. Experimental design and statistical analysis On the basis of single factor studies, response surface methodology (RSM) was used to optimize the conversion yield. Design Expert 8.0 (Stat-Ease Inc., Minneapolis, MN, USA) was used to study the empirical relationship between amylose yield and the four controlled factors: X1: Enzyme dosage; X2: pH; X3: temperature; and X4: time. This design required 29 trials with the independent factors being studied at three different levels. The factors and their levels were: enzyme dosage (70, 100 and 130 IU/ml); pH (4.5, 5.0 and 5.5); temperature (46, 52 and 58 ◦ C); and time (90, 150 and 210 min). All experiments were performed in duplicate with the statistical significance of the terms being examined by ANOVA and a significance test level of 5% (p < 0.05).

L. Hu et al. / International Journal of Biological Macromolecules 86 (2016) 105–111

107

Fig. 1. Response surface diagram for amylose yield as a function of (a) pH and enzyme dose (temperature and reaction time were kept at the central points of 52 ◦ C and 150 min); (b) temperature and enzyme dose (pH and reaction time were kept at the central points of 5.0 and 150 min); (c) temperature and pH (enzyme dose and reaction time was kept at the central points of 100 IU/ml and 150 min); (d) time and pH (enzyme dose and temperature were kept at the central points of 100 IU/ml and 52 ◦ C).

3. Results and discussion 3.1. The modification of isoamylase Enzymatic modification by cleaving the branching point of the ɑ-1,6-linkages and short linear ɑ-1,4 linked glucans is beneficial for forming amylose starch [28]. It has been reported that highamylose starches and their derived products have high resistant starch contents, indicating that the amount of amylose could be an index for resistant starch [29]. To improve the performance of the enzymatic system, response surface methodology (RSM) provided the optimal reaction parameters to increase the conversion efficiency. 3.1.1. Effect of enzyme dose A maximum conversion efficiency of 70.84% was observed after 150 min when the isoamylase dose was 110 IU/ml for the reaction at a temperature of 50 ◦ C and pH 5.2 (Fig. 1a). The yield of amylose increased until the isoamylase concentration reached a dosage level of 110 IU/ml, after which the amylose yield changed little (Fig. 1a). 3.1.2. Effect of pH The amylose yield remained high when the pH was between 4.5 and 5.0, but decreased when the pH was greater than 5.0 (Fig. 1b). The mild acid hydrolysis of starch chains could accelerate starch retrogradation in a paste or gel to increase amylose yield as reported by Chung et al. [30]. This conflicts with Lim et al. [31] who suggested that isoamylase reacted optimally at pH 7.0, but was consistent with Fang et al. [32] who reported that the optimum pH was 5.0.

These differences in optimal pH for the maximal activity of isoamylase may have been caused by the different sources of bacteria used in the production of isoamylase. 3.1.3. Effect of temperature on enzyme conversion The effect of reaction temperature on amylose yield was investigated in the range from 46 to 58 ◦ C. According to Li et al. [33]. isoamylase is a debranching enzyme that can efficiently hydrolyze substrates with a high ratio of branched chains such as glycogen, amylopectin and starch at temperatures from 30 to 70 ◦ C. As shown in Fig. 1c, when the temperature increased from 46 to 52 ◦ C, the yield of amylose increased from 66.61 to 73.82%. However, enzymatic activity decreased as the temperature increased, probably because of enzyme inactivation. A temperature of 52 ◦ C was found to be optimal for isoamylase activity. 3.1.4. Effect of hydrolysis time The effect of hydrolysis time on amylose yield was estimated for times between 90 and 210 min. As shown in Fig. 1d, the amylose yield was enhanced as the hydrolysis time increased up to 170 min, because the isoamylase released glycogenin-bound branched malto-oligosaccharide during hydrolysis. Even after longer hydrolysis times, some linear chains were released by isoamylase. 3.1.5. Response surface analysis for the optimization of amylose levels Figs. 1a-d show the response surface curves for variation in amylose yields. These diagrams make it easier and more convenient to

108

L. Hu et al. / International Journal of Biological Macromolecules 86 (2016) 105–111

Fig. 2. Wavelength scanning profile of normal and high-amylose ginkgo starches binding iodine.

understand the interactions between efficiency in terms of amylose yield and the modification factors and also to locate their optimum levels. The maximal activity of isoamylase occurred at 52 ◦ C and a pH of 5.0. Our results have indicated that under the optimal conditions the maximum amylose yield of 74.74% was observed after 170 min when the enzyme dose was greater than 100 IU/ml. 3.2. Starch-iodine absorbance spectra and amylose content The iodine absorption spectra and blue values and the amylose content of the native and isoamylase-modified ginkgo starch were measured. The wavelength scanning profiles of normal starch and high-amylose starch binding iodine are shown in Fig. 2. The ability of iodine to complex with amylose and amylopectin has been used to estimate the affinity of the polysaccharide structure [34]. As shown in Fig. 2, the iodine binding with normal starch showed a max value of approximately 620 nm, but decreased to about 600 nm after the initial branching enzyme treatment. As shown in Table 1, the higher amylose content of the modified starch was illustrated by the higher blue value compared with normal starch. The amylose content increased from 33.26 to 74.74%, and the blue value from 0.32 to 0.75 with the addition of the branching enzyme. The color and wavelength of maximum absorbance (max ) of the complex are related to the degree of polymerization and average chain length of amylose and amylopectin [35]. Thus, the lower max value and higher blue value of the high-amylose starch in the present study might be caused by the large linear chains. 3.3. Morphology of the starch

Fig. 3. Scanning electron microscopy (SEM) images of (A) normal (×1500), (B) highamylose starch (×1500) and (C) heat-treated starch (×1500).

Images of the three types of ginkgo starch granule are shown in Fig. 3. The micro-structural changes on the surface caused by enzyme treatment can be clearly observed. The normal starch granules were oval or spherical in shape with a smooth surface and no edges (Fig. 3A), although there were some irregular indentations on the surface. The granule size was in the range of 5–20 ␮m measured by the scale bar of microscopy. After modification with isoamylase, the high-amylose starch particles present a very different morphology (Fig. 3B). Unlike the unmodified starch, the particles appear to be larger with a very irregular surface and a porous inner structure. Fig. 3C shows the morphology of the heat-treated starches, which were porous and fragmented with irregular surface. The starch granules absorbed water and expanded during gelatinization. Due

to the extreme expansion, the starch granules start to rupture and the crystalline regions disappears. It can be seen from Fig. 3 that the granule size of heat-treated starch is bigger than that of normal starch and smaller than the high-amylose starch. Compared with the fragmented heat-treated starch, the high-amylose starch is compact and slick and shows spherulites morphology. Modification of the morphology of starch particles through enzyme digestion has been previously described [8]. The coarse honeycomb-like network structure composed of amylose and amylopectin may have been affected by the re-crystallization of the debranched ginkgo starch to form high-amylose starch.

L. Hu et al. / International Journal of Biological Macromolecules 86 (2016) 105–111

109

Table 1 Starch-iodine absorbance, X-ray and gelatinization shifts of normal and high-amylose ginkgo starches. Sample

Normal

High-amylose

Starchiodine absorbanceA

Amylose (%) Blue value max (nm)

33.26 ± 0.42a 0.32 ± 0.04a 620 ± 5a

74.74 ± 0.21b 0.75 ± 0.04b 600 ± 5a

X-rayA

Crystal type Relative crystallinity (%) To ( ◦ C) Tp ( ◦ C) Tc ( ◦ C) T ( ◦ C) Hgel (J/g)

C-type 29.63 ± 0.24b 51.03 ± 0.19b 98.01 ± 0.18a 148.78 ± 0.11a 97.75 ± 0.14a 184.69 ± 0.09b

V-type 19.14 ± 0.27a 44.8 ± 0.22a 109.3 ± 0.21b 148.9 ± 0.15a 104.2 ± 0.22b 63.8 ± 0.27a

Gelatinization propertiesA,B

A B

Data were expressed as x¯ ± SD (n = 3). Mean values followed by different letters in the same row are significantly different (p < 0.05). To : onset temperature; Tp : peak temperature; Tc : conclusion temperature; T: gelatinization range (Tc –To ); Hgel : enthalpy of gelatinization.

the temperature increased. The swelling power of normal starch showed a slight increase up to 65 ◦ C, but then increased significantly as the temperature increased further. There was a significant difference in swelling power between normal and high-amylose ginkgo starch. During gelatinization, high-amylose starch showed a noticeably lower variation in swelling power, but there was no significant increase. Any differences could possibly be attributed to the amylose content and the level of lipid-complexed amylose chains, because amylose and lipids retard the absorption of water, swelling and the pasting of starch granules [39]. Fig. 4B shows that the water solubility of native starch did not increase significantly between 55 and 65 ◦ C, while the solubility of the high-amylose starch increased sharply. The water solubility of both the normal and high-amylose starches increased significantly above 70 ◦ C. The solubility of high-amylose starch increased much more rapidly and was also higher than normal starch. The extent of interaction between swelling power and water solubility is influenced by the contents and characteristics of amylose and amylopectin. The higher water solubility of high-amylose starch may be related to its higher amylose content [40], which would have been leached out from the starch granules into the water. The channels present in starch granules might also have increased the potential surface area available for the reaction and penetration of reagents in the granule [41]. 3.5. Thermal properties

Fig. 4. Swelling power and water solubility of normal and high-amylose ginkgo starch at different temperatures.

3.4. Swelling power and water solubility of starches The swelling power and water solubility of starches have been reported to be influenced by the level of lipid-complexed amyloseamylose chains [36], the total amylose content [37] and the extent of interaction between starch chains within the amorphous and crystalline domains [38]. The swelling power and water solubility at different temperatures are shown in Fig. 4A and B. Both the swelling power and the solubility of the starches increased as

The DSC provided measurements and recordings of the amount of heat involved in starch gelatinization. The DSC parameters of normal and high-amylose starches are shown in Table 1. Normal starch had a higher gelatinization onset temperature of 51.03 ± 0.19 ◦ C and a lower peak temperature of 98.01 ± 0.18 ◦ C compared with those of high-amylose ginkgo starch, 44.8 ± 0.22 ◦ C and 109.3 ± 0.21 ◦ C, respectively. A broader range of gelatinization transition temperatures suggests the presence of crystallites with varying stability within the crystalline domains of the granule in high-amylose starch [42]. The amylose double helices and greater heterogeneity in the crystallite populations within the granules also require a high temperature and energy input to become disordered, which leads to a high gelatinization temperature [43]. Compared with their regular counterparts, high-amylose starch has been characterized by a lower average H which depends on the amylose content and physical structure [15]. As a result, the differences in amylose content, crystalline and physical structure led to different thermal properties. 3.6. X-ray diffraction patterns The X-ray diffraction patterns and relative crystallinity of normal and debranched starches are shown in Fig. 5 and Table 1.

110

L. Hu et al. / International Journal of Biological Macromolecules 86 (2016) 105–111

cation. Starch granules showed an irregular surface and porous inner structure after enzyme hydrolysis. X-ray diffraction patterns showed that the crystallinity changed from the C-type to the V-type as the amylose content increased. High-amylose starch had a higher blue value and water solubility and a lower crystallinity, swelling power, and pasting enthalpy than that of normal ginkgo starch. The present study has indicated that the high-amylose starch prepared from isoamylase has unique functional properties, which lays the foundation for the wider application of ginkgo starch.

Author contributions C. Yao conceived the idea and designed the experiments. L. Hu prepared the samples and performed characterization with the assistance from Y. Zheng and Y. Peng. C. Yao discussed with L. Hu and H. Zhang for the analysis and discussion of results. L. Hu and C. Yao were mainly responsible for preparing the manuscript with further inputs from other authors. All the authors discussed the results and commented on the manuscript. Fig. 5. X-ray diffraction of normal and high-amylose starch samples.

Previous studies have reported that native ginkgo starch displayed a C-type crystalline diffraction pattern with diffraction angles 2 of 5.6◦ , 15◦ , 17◦ , 18◦ and 23◦ [1,2]. After treatment, the modified starch showed a strong diffraction peak at 2 with values of around 13◦ , 15◦ , 17◦ , 18◦ , 20◦ , 23◦ and 24◦ . An A-type signature reflection at 2 with values of doublet diffraction of 17◦ and 18◦ and 23◦ and V-type signature reflection at 2 with values of 15◦ and 20◦ were absent. This evidence indicated that the patterns of the high-amylose starch displayed a mixture of A- and V-types [44]. V-type crystallites have been shown to melt at a higher temperature than C-type crystallites, leading to an increase in To and Tp . This agreed with Zhang et al. [45] who reported an amorphous form that melts at a lower temperature (Tp ∼100 ◦ C) and a crystalline form with a V-type structure and a higher melting temperature (Tp > 100 ◦ C). Compared with native starch, the intensity of the 20◦ peak which represents a characteristic amylose-lipid complex diffraction peak was greater in high-amylose starch. This was attributed to debranching and retrogradation which greatly improved the percentage of amylose and promoted single amylose helices complexed with polar and non-polar compounds. Table 1 shows that the native starch had a lower amylose content and a higher crystallinity of 29.63% ± 0.24%, while the high-amylose starch had a higher amylose content and a lower crystallinity of 19.14% ± 0.27%. Obviously, the relative crystallinity of starch decreased as the amylose content increased. These results were consistent with Cai et al. [46]. The range of gelatinization temperatures has been reported to be related to the heterogeneity of crystallites within the starch granules [27]. The lower onset temperature was consistent with the lower crystallinity since perfect crystals or a higher co-operative unit needs a higher level of gelatinization [27]. The lower relative crystallinity of high-amylose starch provides direct evidence of high water solubility, because the water can penetrate into the more accessible amorphous regions of the starch granule. 4. Conclusions In the present study, isoamylase was used as a debranching enzyme to hydrolyze branched chains of starch to form highamylose starch. The experiments using RSM showed that the maximum amylose yield of 74.74% was observed after 170 min when the enzyme dose was greater than 100 IU/ml and the system was maintained at 52 ◦ C and pH 5.0. The morphology, crystallinity and thermal properties were significantly changed after modifi-

Acknowledgments This study was financially supported by the Science and Technology Program of Taizhou Municipal Government (Project No.TG201421), Supported by the Open Project Program of State Key Laboratory of Food Science and Technology, Jiangnan University (No. SKLF-KF-201505) and the Taizhou Municipal 311 personnel training program.

References [1] M. Miao, H. Jiang, B. Jiang, S.W. Cui, Z. Jin, T. Zhang, Food Res. Int. 49 (2012) 303–310. [2] K.E. Spence, J. Jane, Carbohydr. Polym. 40 (1999) 261–269. [3] L. Wang, B. Xie, G. Xiong, W. Wu, J. Wang, Y. Qiao, L. Liao, Food Hydrocolloids 31 (2013) 61–67. [4] L. Lin, D. Guo, L. Zhao, X. Zhang, J. Wang, F. Zhang, C. Wei, Food Hydrocolloids 52 (2016) 19–28. [5] F. Vilaplana, D. Meng, J. Hasjim, R.G. Gilbert, Carbohydr. Polym. 113 (2014) 539–551. [6] L. Cai, Y.C. Shi, Carbohydr. Polym. 79 (2010) 1117–1123. [7] W.S. Ratnayake, R. Hoover, F. Shahidi, C. Perera, J. Jane, Food Chem. 74 (2001) 189–202. [8] J. Pongjanta, A. Utaipattanaceep, O. Naivikul, K. Piyachomkwan, Carbohydr. Polym. 78 (2009) 5–9. [9] A.M. Leeman, M.E. Karlsson, A.C. Eliasson, I.M.E. Bjorck, Carbohydr. Polym. 65 (2006) 306–313. [10] S. Wang, J. Wang, J. Yu, S. Wang, Food Chem. 164 (2014) 332–338. [11] A. Cano, A. Jiménez, M. Cháfer, C. Gónzalez, A. Chiralt, Carbohydr. Polym. 111 (2014) 543–555. [12] S.Y. Guan, P.W. Wang, H.J. Liu, G.N. Liu, Y.Y. Ma, L.N. Zhao, Afr. J. Biotechnol. 68 (2011) 15229–15237. [13] L.L. Jiang, X.M. Yu, X. Qi, Q. Yu, S. Deng, B. Bai, N. Li, A. Zhang, C.F. Zhu, B. Liu, Transgenic Res. 6 (2013) 1133–1142. [14] K. Kansou, A. Buleon, C. Gerard, A. Rolland-Sabate, Carbohydr. Polym. 133 (2015) 497–506. [15] M. Schirmer, A. Höchstötter, M. Jekle, E. Arendt, T. Becker, Food Hydrocolloids 32 (2013) 52–63. [16] C. Cai, C. Wei, Carbohydr. Polym. 92 (2013) 469–478. [17] A. Regina, J. Blazek, E. Gilbert, B.M. Flanagan, M.J. Gidley, C. Cavanagh, J.P. Ral, O. Larroque, A.R. Bird, Z. Li, M.K. Morell, Carbohydr. Polym. 89 (2012) 979–991. [18] M.K. Morell, B. Kosar-Hashemi, M. Cmiel, M.S. Samuel, P. Chandler, S. Rahman, A. Buleon, L. Batey, Z.Y. Li, Plant J. 2 (2003) 173–185. [19] Y.H. Leong, A.A. Karim, M.H. Norziah, Starch-Stärke 59 (2007) 21–32. [20] B. Zhang, L. Chen, Y. Zhao, X. Li, J. Cereal Sci. 57 (2013) 348–355. [21] L.J. Zhu, Q.Q. Liu, J.D. Wilson, M.H. Gu, Y.C. Shi, Carbohydr. Polym. 86 (2011) 1751–1759. [22] Y. Zheng, H. Zhang, C. Yao, L. Hu, Y. Peng, J. Shen, Food Hydrocolloids 48 (2015) 312–319. [23] P.V. Huang, T. Maeda, D. Miskelly, R. Tsumori, N. Morita, Carbohydr. Polym. 71 (2008) 656–663. [24] D. Lu, X. Shen, X. Cai, F. Yan, W. Lu, Y.C. Shi, Food Chem. 143 (2014) 313–318. [25] A.A. Karim, M.Z. Nadiha, F.K. Chen, Y.P. Phuah, Y.M. Chui, A. Fazilah, Food Hydrocolloids 22 (2008) 1044–1053.

L. Hu et al. / International Journal of Biological Macromolecules 86 (2016) 105–111 [26] R.G. Utrilla-Coello, M.E. Rodriguez-Huezo, H. Carrillo-Navas, C. Hernandez-Jaimes, E.J. Vernon-Carter, J. Alvarez-Ramirez, Carbohydr. Polym. 101 (2014) 154–162. [27] M. Miao, B. Jiang, T. Zhang, Z. Jin, W. Mu, Food Chem. 126 (2011) 506–513. [28] T.T. Huang, D.N. Zhou, Z.Y. Jin, X.M. Xu, H.Q. Chen, Food Chem. 187 (2015) 218–224. [29] A. Htoon, A.K. Shrestha, B.M. Flanagan, A. Lopez-Rubio, A.R. Bird, E.P. Gilbert, M.J. Gidley, Carbohydr. Polym. 75 (2009) 236–245. [30] H.J. Chung, H.Y. Jeong, S.T. Lim, Carbohydr. Polym. 54 (2003) 449–455. [31] W.J. Lim, S.R. Park, S.J. Cho, M.K. Kim, S.K. Ryu, S.Y. Hong, W.T. Seo, H. Kim, H.D. Yun, Biochem. Biophys. Res. Commun. 287 (2001) 348–354. [32] T.Y. Fang, W.C. Tseng, C.J. Yu, T.Y. Shih, J. Mol. Catal. B 33 (2005) 99–107. [33] Y. Li, L. Zhang, Z. Ding, G. Shi, Process Biochem. 48 (2013) 1303–1310. [34] X. Shen, E. Bertoft, G. Zhang, B.R. Hamaker, Carbohydr. Polym. 98 (2013) 778–783. [35] M. Miao, S. Xiong, B. Jiang, H. Jiang, S.W. Cui, T. Zhang, Food Hydrocolloids 38 (2014) 180–185.

[36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46]

111

R.F. Tester, W.R. Morrison, Cereal Chem. 6 (1992) 654–658. T. Sasaki, J. Matsuki, Cereal Chem. 4 (1998) 525–529. R. Hoover, H. Manuel, J. Cereal Sci. 2 (1996) 153–162. F. Qin, J. Man, C. Cai, B. Xu, M. Gu, L. Zhu, Y.C. Shi, Q. Liu, C. Wei, Carbohydr. Polym. 88 (2012) 690–698. C. Wei, F. Qin, W. Zhou, B. Xu, C. Chen, Y. Chen, Y. Wang, M. Gu, Q. Liu, Food Chem. 128 (2011) 645–652. J. Man, F. Qin, L. Zhu, Y.-C. Shi, M. Gu, Q. Liu, C. Wei, Food Chem. 134 (2012) 2242–2248. J. Huang, Z. Shang, J. Man, Q. Liu, C. Zhu, C. Wei, Food Hydrocolloids 46 (2015) 172–179. J. Cai, Y. Yang, J. Man, J. Huang, Z. Wang, C. Zhang, M. Gu, Q. Liu, C. Wei, Food Chem. 145 (2014) 245–253. M. Shi, Q. Gao, Carbohydr. Polym. 84 (2011) 1151–1157. B. Zhang, Q. Huang, F. Luo, X. Fu, Food Hydrocolloids 28 (2012) 174–181. J. Cai, J. Man, J. Huang, Q. Liu, W. Wei, Carbohydr. Polym. 125 (2015) 35–44.