Slow digestion property of microencapsulated normal corn starch

Slow digestion property of microencapsulated normal corn starch

Journal of Cereal Science xxx (2014) 1e6 Contents lists available at ScienceDirect Journal of Cereal Science journal homepage: www.elsevier.com/loca...

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Journal of Cereal Science xxx (2014) 1e6

Contents lists available at ScienceDirect

Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs

Slow digestion property of microencapsulated normal corn starch Hui Xu, Genyi Zhang* State Key Laboratory of Food Science and Technology, School of Food Science, Jiangnan University, Lihu Avenue 1800, Wuxi 214122, People’s Republic of China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 13 November 2013 Received in revised form 27 January 2014 Accepted 28 January 2014

Starch is the main glycemic dietary carbohydrate, and its nutritional quality is associated with the amount of slowly digestible starch (SDS) that is beneficial to glycemic control. In the current study, a microencapsulation of normal corn starch by zein protein and its slow digestion property were investigated. A significant increase of SDS and RS was shown for starch capsules (weight ratio of zein to starch: 1:6) containing plasticizers of glycerol and oleic acid after high temperature (70  C) treatment. Further studies showed a substantially decreased viscosity and the formation of an amyloseelipid complex after starch gelatinization. Thus, the hydrophobic physical barrier of the zein matrix and the amyloseelipid complex might together limit the water accessibility and starch swelling leading to a dense packing of starch materials with a high amount of SDS. The acceptable sensory property makes it an ideal ingredient for specialty food preparation and glycemic control. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Slowly digestible starch Microencapsulation Glycemic control Zein

1. Introduction Starch, as the main component of cereal grains, is an important dietary carbohydrate providing energy for a series of physiological processes in which the brain is the major consumer of glucose (Fehm et al., 2006) for normal activity of the central nervous system such as cognition development (Gold, 1995). In the mean time, a prevalence of glucose metabolism related diseases such as type 2 diabetes indicates the supply of glucose to the body needs to be better controlled for glucose homeostasis (Le et al., 2013). Thus, the nutritional properties of starch that are expressed by the percentage of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) (Englyst et al., 1992) need to be improved with a high amount of beneficial glycemic SDS (Lehmann and Robin, 2007), which is distinctly different from RDS that is a causative factor for many chronic diseases (Ells et al., 2005). Literature reports also showed that SDS epigenetically caused a shift of the gene expression peak of SGLT1 from the upper jejunum to ileum (Shimada et al., 2009) leading to an increased glucose transporter

Abbreviations: ENS, microencapsulated starch; ENSP, encapsulated starch containing plasticizer; GLP-1, glucagon-like peptide-1; GOPOD, glucose oxidase/ peroxidase; NCS, non-encapsulated starch (or normal corn starch); RS, resistant starch; RVA, rapid visco analyzer; SDS, slowly digestible starch; SEM, scanning electron microscopy; SGLT1, Na(þ)-D-glucose cotransporter. * Corresponding author. Tel.: þ86 510 85328726. E-mail address: [email protected] (G. Zhang).

in the ileum (Woodward et al., 2012). High glucose content in the ileum after consuming SDS can result in sustained increase of an incretin hormone of GLP-1 (Wachters-Hagedoorn et al., 2006) that is important for body weight regulation and insulin sensitivity (Larsen, 2008). Thus, SDS not only generates a moderate postprandial glycemic response but also influences a variety of physiological processes that are essential to human health. The scarcity of SDS, however, in regular food products (Bjorck et al., 2000) limits its practical applications, and techniques to produce SDS are critical to make its health benefit a reality. Based on our study, the native cereal starch is the ideal SDS made by nature (Zhang et al., 2006a), however, its slow digestion property almost completely disappeared once it is gelatinized (Zhang et al., 2008). Although there have been reports (Han and BeMiller, 2007; Venkatachalam et al., 2009) or patents on the preparation of SDS, most of them are either thermal sensitive or do not have a significant amount of SDS for noticeable health outcomes. Considering the slow digestion property of native cereal starch is an enzyme concentration-independent physical entity (Zhang et al., 2006b) that can resist the conditional regulation of the body, it would be the ideal SDS for consumption. However, the consumers are not willing to sacrifice the taste to accept the consumption of raw starch. Microencapsulation is commonly used to mask the flavor of food materials, and microencapsulation of cereal starch granules to reduce their raw taste might be a possible way for consumers to accept the consumption of raw starches. Since normal corn starch is

http://dx.doi.org/10.1016/j.jcs.2014.01.021 0733-5210/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Xu, H., Zhang, G., Slow digestion property of microencapsulated normal corn starch, Journal of Cereal Science (2014), http://dx.doi.org/10.1016/j.jcs.2014.01.021

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H. Xu, G. Zhang / Journal of Cereal Science xxx (2014) 1e6

the most commonly used cereal starch, and zein protein has been widely used as shell materials for encapsulation (Parris et al., 2005), they were chosen as the core and shell materials to produce microencapsulated starch to mimic the natural forms of starch and protein in corn grains. The resulted digestion properties of microencapsulated starches were studied, and it is expected that specialty food focused on postprandial glycemic control could be prepared using the microencapsulated starch materials. The coexistence of corn starch and zein in corn flour might also be technologically advantageous to produce this type of encapsulated starch material. 2. Materials and methods 2.1. Chemicals Zein protein (soluble in 80e92% ethanol) extracted and purified from corn protein powder was obtained from Wujiang City Bache Pharmaceutical Adjuvant Factory (Wu Jiang, China) with a moisture content of w8.0%. The Kjeldahl test showed a nitrogen content of 15.0% (dry weight basis) that is equal to a purity of w94% converted by a factor of 6.25. Glycerol (ACS reagent, 99.5%) and oleic acid (99%, GC) were purchased from SigmaeAldrich (Shanghai, China). Low methoxyl pectin was from Quzhou Pectin Co., LTD., (Quzhou, China), and its degree of esterification is w35%. Normal maize starch (amylose content: w25%) was obtained from National Starch and Chemical Company (Shanghai, China). a-Amylase (EC 3.2.1.1, type VI-B from porcine pancreas, 19.6 U/mg) and AMG (EC 3.2.1.3, from Rhizopus mold, 21.1 U/mg) were purchased from Sigma Chemical Co. (Shanghai, China). The glucose oxidase/peroxidase (GOPOD) kit for D-glucose assay was from Megazyme International Ireland Ltd. (Wicklow, Ireland). 2.2. Low-temperature spray drying for starch encapsulation A lab scale low-temperature spray dryer (Model yc-015A, Pilotech, Shanghai, China) was used to encapsulate normal corn starch. The slurry containing zein protein (dissolved in 80% ethanol) and starch granules with or without plasticizers of glycerol and oleic acid (20% based on zein weight in a ratio of 1:3) was stirred for 30 min at 60  C. After homogenization at 30 Mpa, the sample was spray dried using the low-temperature spray drier with an entrance temperature of 120  C and exit temperature of 90  C at a flow rate of 15 mL/min. The dried sample was bottled for analysis.

gavages. For all the samples, a 2.5% low methoxyl pectin solution was used to prepare the test samples (glucose, starch, encapsulated starch). Blood samples were taken from the lateral tail vein at 0, 15, 30, 45, 60, 90, and 120 min after gavages. The blood glucose concentration was measured using a glucose analyzer (Medisense, Abbott Park, IL) and expressed as the mean  standard error (S.E.). All the procedures were approved by the Experimental Animal Review Committee at Jiangnan University of China. 2.5. Pasting property analysis The pasting property of the encapsulated starch was measured by a rapid visco analyzer (RVA) (StarchMaster2, Perten instruments, Sweden) according to the standard method from the manual. In this procedure, the starch-based slurry (8%) with a final weight of 25.0 g by adding purified water was subjected to a temperature regime of increase from 50 to 95  C, a holding period at 95  C, and a decrease from 95 to 50  C with a subsequent holding period at 50  C. For zein-encapsulated starch samples, the amount used was based on the same starch content. 2.6. X-ray powder diffraction analysis A Bruker D8-Advance diffractometer (Bruker AXS Corp., Nanjing, China) equipped with Cu Ka radiation at 40 kV and 40 mA was used to obtain the X-ray diffractogram of the encapsulated starch by scanning from 3 to 40 2q at a rate of 0.02 /3s. 2.7. In vitro starch hydrolysis The standard Englyst method (Englyst et al., 1992) with minor modifications was employed to measure the starch fractions of RDS, SDS and RS. Briefly, 200 mg prepared starch samples in 5 mL buffer (100 mM NaOAC, pH 5.2, CaCl2 4 mM) with 6 glass beads (5 mm diameter)/tube was pretreated in a water bath for various temperatures (50, 60, 70, 80, 90, 100  C) for 10 min with continuous shaking at 120 rpm. After all the tubes were cooled to 37  C, 5 mL preheated (37  C) dual enzyme solution (580 U/mL porcine pancreatic a-amylase, 12 U/mL amyloglucosidase) was added for digestion with continuous shaking at 120 rpm. An aliquot digestion sample (0.5 mL) was taken out at 20 and 120 min, and then 5 mL ethanol was added to stop the reaction. The released glucose was measured based on the procedure of GOPOD assay kit. The content of RDS, SDS and RS was calculated by taking a converting factor of 0.9 and expressed as the average and standard deviation.

2.3. Scanning electron microscopy (SEM) analysis 2.8. Sensory evaluation To analyze the morphological changes of starch granules after encapsulation, the encapsulated sample was first fixed by osmium tetroxide and sputter coated with platinum to a level of 250e 500 nm. Scanning electron micrographs were then obtained with a Quanta 200 scanning electron microscope (FEI Co., Switzerland) under a vacuum of 13.33 Pa and an operating voltage of 20 kV. 2.4. Postprandial glycemic response measurement Nine week-old male Kunmin (km) mice were purchased from Silaike Co. (Shanghai, China) and kept under an automatic light schedule of 07:00 a.m.e19:00 p.m. and a temperature at 22  3  C. The mice were conditioned by feeding ad libitum with a laboratory chow diet (Silaike Co. Shanghai, China) and drinking water. Experiments were performed one week later after an overnight fasting (10 mice per group). The postprandial glycemic response to zein-encapsulated starch was then measured by feeding the test samples (starch, 1 g/kg body weight [BW]) administrated via

Ten professional sensory evaluators were chosen to evaluate the sensory properties of the samples focusing on the chewiness, graininess and overall acceptability. The chewiness refers to the rawness of the samples, and the graininess refers to the coarseness due to particles size of the encapsulated starch granules. A 7 point scale from 1 to 7 was used to represent categories from poor to excellent. For chewiness, 1 means the rawness is very strong, 2 means strong, 3 means less strong, 4 means mild, 5 means weak, 6 means weaker, and 7 means the weakest. For graininess, 1 means very coarse, 2 means less coarse, 3 means least coarse, 4 means mild, 5 means a little smooth, 6 means smooth, and 7 means the most smoothness. For acceptability, 1 means the weakest likeness, 2 means weaker likeness, 3 means weak likeness, 4 means mild, 5 means a little likeness, 6 means likeness, 7 means highest likeness. The sample for the sensory test was prepared by dissolving 30 g milk powder in 300 mL distilled water at 100  C, and then a 20 g sample of encapsulated starch was added at 50, 60, 70 and 80  C.

Please cite this article in press as: Xu, H., Zhang, G., Slow digestion property of microencapsulated normal corn starch, Journal of Cereal Science (2014), http://dx.doi.org/10.1016/j.jcs.2014.01.021

H. Xu, G. Zhang / Journal of Cereal Science xxx (2014) 1e6

The sample for comparison between native starch and encapsulated starch was prepared similarly as above at 60  C by adding 20 g corn starch or 20 g encapsulated starch to 300 mL milk prepared by milk powder that acted as the control. The sensory properties of the samples were evaluated when the samples were cooled to room temperature, and the values for each sensory parameter were obtained by adding all the numerical numbers from each evaluator. 2.9. Statistical analysis

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Table 1 The digestion of encapsulated starch with different ratio of zein to starch. Sample (Zein:Starch)

RDS%

Starch 1:4 1:6 1:8 1:10 1:20 1:6 þ plasticizer

26.77 21.05 13.81 19.97 19.25 23.35 13.96

SDS%       

0.00a 0.00b 0.00c 0.09d 0.01d 0.00e 0.00c

53.43 57.22 57.22 50.39 58.37 53.92 57.42

RS%       

0.00a 0.00b 0.01b 0.22c 0.01b 0.01a 0.01b

19.80 21.73 28.97 29.63 22.39 22.73 28.62

      

0.00a 0.00b 0.01c 0.10c 0.00b 0.00b 0.01c

Notes: a,b,c,d,e represent significant difference (P < 0.05).

Triple replications of measurement with means and standard deviation were applied to the starch digestion data, and the standard error was used for the glycemic response. The significant difference at P < 0.05 was analyzed using an SPSS software (version 17.0, IBM). 3. Results and discussion 3.1. Preparation of microencapsulated normal corn starch In the current process of starch encapsulation, zein protein was selected as the shell or matrix material to encapsulate starch granules based on its alcohol-soluble property. For starch encapsulation, 80% ethanol solvent was used first to solubilize the zein protein, and then other materials were added, homogenized and finally spray dried to produce encapsulated starch materials. Except the starch granules used as the core material of microencapsulation, two types of plasticizers of glycerol and oleic acid were also incorporated in the microencapsulation process for the purpose of enhancing the mechanical properties of zein matrix with increased tensile strength and elongation to break (Xu et al., 2012). This is because the zein film or zein matrix without any plasticizers is very brittle and easy to be broken (Lawton, 2004).

After a low-temperature spray drying process, the encapsulated starch particles were formed (Fig. 1A). The almost spherical particle is composed of multiple starch granules embedded in the zein protein matrix. The particle size of the encapsulated starch granules is dependent on the ratio of starch to zein protein. Generally, the particle size becomes smaller as the increase of core material of starch, and some starch granules may not be completely encapsulated when the ratio of zein protein to starch was too low as observed by SEM (Fig. 1B). Thus, an appropriate ratio between starch and zein protein need to be determined for starch encapsulation. 3.2. In vitro starch hydrolysis of encapsulated starch The slow digestion properties of encapsulated starch samples were examined by the Englyst method (Englyst et al., 1992). All the starch samples had a similar amount of SDS independent of the ratios of zein to starch (Table 1), but the RDS decreased from the starch control of 26.8%e13.8% for encapsulated starch at a zein to starch ratio of 1:6, and then increased with the decrease of the zein to starch ratios. In contrast, the RS content was increased from the control of 19.8% to the highest of 29.6% for encapsulated starch at a

Fig. 1. The morphological changes of encapsulated starch granules at a weight ratio of zein to starch at 1:4 (A), 1:10 (B), and 1:6 (C) containing plasticizer of glycerol and oleic acid (D).

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zein to starch ratio of 1:8, and then decreased with the decrease of zein to starch ratios. Apparently, the changes of RDS and RS with the zein to starch ratios demonstrate that there needs to be an optimum ratio of zein to starch, which is likely a critical point for a maximum encapsulation and minimal aggregation among zein protein molecules through hydrophobic interaction. The ratio of 1:6 of zein to starch (Fig. 1C) is likely the optimum condition for starch encapsulation since the encapsulated starch had the lowest RDS that was advantageous to produce more SDS and RS. Under this condition, starch was also fully embedded in the zein matrix, microencapsulation containing the plasticizer of glycerol and oleic acid was also made successfully with spherical and tightly packed starch granules in the zein matrix (Fig. 1D), and both of them also have comparable digestion properties (Table 1). The slow digestion property of encapsulated starches was also confirmed by an in vivo study using a mouse model. Both the corn starch material and plasticizer-containing encapsulated starch material showed a slow digestion profile (Fig. 2) with a prolonged and sustained elevation of blood glucose, confirming that the microencapsulation did not change the inherent slow digestion property of native normal corn starch (Zhang et al., 2006a). In other words, starch encapsulation, even in the presence of plasticizers, did not prevent enzymes to digest the embedded starch granules, and the physiochemical property of starch is still the main determinant of the slow digestion properties of the encapsulated starch samples. 3.3. In vitro starch hydrolysis of high temperature-treated samples Although all the encapsulated starches showed a high content of SDS when the starch is not gelatinized, it is still difficult for consumers to accept the encapsulated starches as some type of food for consumption. Thus a thermal treatment of the encapsulated starch was carried out to understand the function of microencapsulation in starch digestion when the samples were pretreated at different temperatures. When the pretreatment temperature was 50  C, that is below the gelatinization temperature of normal corn starch, the digestibility of the control starch was much higher than the two different encapsulated starch samples that had similar content of RDS, SDS and RS. This indicates that the physical barrier of the zein matrix does play certain roles in the digestion of starch, and is consistent with the in vitro hydrolysis of encapsulated samples in which starch was not gelatinized (Table 1). However, when the pretreatment temperature was further increased, different digestion properties were shown among non-encapsulated starch (NCS), Fig. 3. Digestibility of encapsulated starch samples. Starch: normal corn starch, ENS: zein-encapsulated starch, ENSP: encapsulated starch containing plasticizers.

Fig. 2. The postprandial glycemic response to different starch samples. NCS: normal corn starch, EN-NCS: encapsulated normal corn starch in the presence of plasticizer.

microencapsulated starch (ENS), and encapsulated starch containing plasticizers (ENSP). For the treatment at 60  C, the SDS contents were similar, but the values of RDS and RS were different, and ENSP had the lowest RDS and highest RS. As the pretreatment temperature increased to 70  C, which is approaching the temperature for starch gelatinization, zein encapsulation significantly increased the content of SDS and RS, and the addition of plasticizer during microencapsulation further significantly improved the slow digestion property of the encapsulated starch (Fig. 3). After the pretreatment temperature was increased to 80  C, 90  C and 100  C, the same trend of digestibility was maintained, and the ENSP sample still had a good amount of SDS and RS with the lowest of RDS compared to other samples (Fig. 3). Since the addition of glycerol and oleic acid could synergistically improve the tensile strength of zein film (Xu et al., 2012), the increased SDS and RS content of ENSP samples at high temperature treatment indicates

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H. Xu, G. Zhang / Journal of Cereal Science xxx (2014) 1e6 Table 2 The sensory comparison between native corn starch and encapsulated starch (containing plasticizers) after pretreatment at 60  C. Attribute

Sample

1

2

3

4

5

6

7

8

9

10

Total

Chewiness

Control Starch En-starch

7 4 5

6 3 4

7 4 6

7 2 5

6 2 5

6 3 4

7 2 6

6 2 6

7 2 5

6 2 4

65 26 50

Graininess

Control Starch En-starch

6 4 3

7 5 4

7 4 3

7 3 3

7 3 3

5 4 4

6 4 4

7 5 3

7 4 3

5 5 5

64 41 35

Control Starch En-starch

7 4 4

5 3 5

6 3 3

6 3 5

6 2 4

6 2 4

5 1 4

7 3 4

6 2 4

6 3 4

60 26 41

Acceptability

the improved mechanical property of zein matrix might help the encapsulated starch particles to maintain their structural integrity through resisting the mechanical force during digestion. Otherwise, the zein matrix with high tensile strength might also improve the physical barrier property so as to improve the resistance of the encapsulated starches to digestion after high temperature treatment. Apparently, microencapsulation generated a physical barrier to the digestion of encapsulated starch and improved the resistance of starch granule expansion to thermal treatment. Regarding the functions of physical barrier and thermal-resistance of starch due to the zein matrix, the physical barrier may not so effectively prevent the accessibility of enzyme to encapsulated starch when starch is not gelatinized, but the improved resistance to thermal treatment of the starch granule in expansion induced by microencapsulation, especially in the presence of plasticizers, is likely due to the hydrophobic physical barrier to water absorption, which might lead to

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a dense packing of starch granules and a slow digestion property of encapsulated starches after high temperature treatment. Indeed, the statistical analysis showed significant difference in digestion properties between these samples (Supplemental data Table 1), which demonstrates the function of the physical barrier due to zein microencapsulation and the highest resistance to thermal treatment of zein shell in the presence of plasticizers. 3.4. Rapid visco analyzer (RVA) analysis In order to further characterize the microencapsulated normal corn starch and its thermal sensitivity, specifically the ENSP with highest SDS and RS after a high temperature pretreatment, the pasting property of encapsulated starch particles of ENSP were analyzed by a Rapid Visco Analyzer. The results showed dramatic difference in the RVA profiles of normal corn starch and the encapsulated counterpart (Supplementary data Fig. 1, Table 2). The temperature at peak viscosity was increased, and the peak viscosity was substantially decreased for the microencapsulated starch, which indicates an improved thermal-resistance after microencapsulation and is consistent with the results from the in vitro hydrolysis. Additionally, the decreased breakdown, trough, final viscosity and setback showed that both the swelling of encapsulated starch granules (the major determinant for viscosity and breakdown) and the release of amylose (related to setback) were decreased, which suggests a dense packing of starch granules in the zein matrix after a high temperature treatment, and this may slow the enzyme digestion leading to a relatively high amount of SDS. As it is well known that zein is a hydrophobic protein, the hydrophobicity and mechanical force of the plasticized zein matrix (Xu et al., 2012) might together cause resistance to water absorption and decreased starch swelling.

Fig. 4. X-ray powder diffraction of encapsulated starches (containing plasticizer) after pretreatment for 10 min under different temperatures. S: starch, the number represents the temperature.

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3.5. X-ray powder diffraction analysis The semicrystalline structure of starch granules is one of the most important factors affecting its digestibility. Since the ENSP sample has the highest resistance to thermal treatment, the X-ray powder diffraction was used to analyze the effect of plasticizer-containing microencapsulation on the crystalline structure of starch granules after different temperature treatments. The experimental result (Fig. 4A) showed the A-type X-ray diffraction pattern (peaks at w15, 17, 18, and 23 ) was not changed by encapsulation, but a slight decrease of crystallinity was detected in the encapsulated starch that is likely due to the temperature (60  C) used in the process of microencapsulation, which is supported by the similar diffraction patterns of normal corn starch and the encapsulated counterpart after a pretreatment at 60  C (Fig. 4B). The amorphous X-ray diffraction pattern showed that the starch becomes gelatinized after treatment at 70  C, and for its encapsulated counterpart, a release of amylose occurred, which is evidenced by a trace of v-type crystalline structure formed between amylose and lipids (Fig. 4C). When the samples were pretreated at 80  C, a v-type X-ray diffraction pattern (peaks at 13 and 19.5 ) of the encapsulated starch becomes more pronounced (Fig. 4D) indicating the formation of an amyloseelipid complex that is generally difficult to be digested (Zhang et al., 2010). The lipid component may come from the starch itself and/or the zein matrix in which oleic acid was used as a plasticizer. Collectively, the microencapsulation is not likely capable of retaining the crystalline structure of starch after high temperature treatment, but the formation of amyloseelipid complex is another factor contributing to the slow digestion property of ENSP. This is by limiting the swelling of starch granules since the swelling is a property of amylopectin while lipids and amylose inhibit the swelling of starch granules (Tester and Morrison, 1990). The inhibitory effect of lipid on the digestion property of ENSP is due to the formation of amyloseelipid complex that is difficult to be digested (Zhang et al., 2010) and a limited swelling of starch granules that reduces the enzyme accessibility to starch substrate. 3.6. Sensory test Although the microencapsulated starches, particularly the plasticizer-containing encapsulated starches, have a high amount of SDS even after high temperature treatment, their organoleptic properties are an important factor determining their acceptability by consumers. Therefore, the sensory test using a 7 point scale was carried out focusing on the chewiness and coarseness of the samples prepared in a beverage form combined with milk after different temperature treatments. The score from 1 to 7 represents different categories from dislike extremely to neutral, and then to like it greatly. The sensory test showed a rapid decrease of acceptability when the temperature was above 70  C (Supplementary data Table 3), so a temperature of 60  C was used to compare the sensory property of raw starch and encapsulated starch (containing the plasticizer) (Table 2). Although the graininess of the encapsulated sample was a little less than that of starch due to its particle size, the chewiness was improved, and the overall acceptability also improved substantially. Thus, the plasticizercontaining encapsulated starch can be used as a food ingredient for postprandial glycemic control or can be used directly in a beverage form as a specialty food for human consumption. In conclusion, the slow digestion property of zein-encapsulated starch was investigated, and the granular structure of starch is the predominant factor determining the digestibility of the

encapsulated samples. The hydrophobic physical barrier formed by zein matrix, the mechanical property of the zein matrix, and the amyloseelipid complex all contribute to the digestion property of encapsulated starches depending on the temperature and the status of starch gelatinization. In order to achieve a maximum effect on health with the highest SDS, encapsulated starch can be directly used in a beverage form, or it can be used as a food ingredient to prepare specialty food for human consumption. Acknowledgment The current investigation was supported by the Chinese Natural Science Foundation (project No: 21076095). Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jcs.2014.01.021. References Bjorck, I., Liljeberg, H., Ostman, E., 2000. Low glycaemic-index foods. Br. J. Nutr. 83, S149eS155. Ells, L.J., Seal, C.J., Kettlitz, B., Bal, W., Mathers, J.C., 2005. Postprandial glycaemic, lipaemic and haemostatic responses to ingestion of rapidly and slowly digested starches in healthy young women. Br. J. Nutr. 94, 948e955. Englyst, H.N., Kingman, S.M., Cummings, J.H.,1992. Classification and measurement of nutritionally important starch fractions. Eur. J. Clin. Nutr. 46 (Suppl. 2), S33eS50. Fehm, H.L., Kern, W., Peters, A., 2006. The selfish brain: competition for energy resources. Prog. Brain Res. 153, 129e140. Gold, P.E., 1995. Role of glucose in regulating the brain and cognition. Am. J. Clin. Nutr. 61, 987Se995S. Han, J.-A., BeMiller, J.N., 2007. Preparation and physical characteristics of slowly digesting modified food starches. Carbohydr. Polym. 67, 366e374. Larsen, P.J., 2008. Mechanisms behind GLP-1 induced weight loss. Br. J. Diabetes Vasc. Dis. 8, S34eS41. Lawton, J.W., 2004. Plasticizers for zein: their effect on tensile properties and water absorption of zein films. Cereal Chem. 81, 1e5. Le, P.T., Huisingh, C.E., Ashraf, A.P., 2013. Glycemic control and diabetic dyslipidemia in adolescents with type 2 diabetes. Endocr. Pract. 19, 1e16. Lehmann, U., Robin, F., 2007. Slowly digestible starch-its structure and health implications: a review. Trends Food Sci. Technol. 18, 346e355. Parris, N., Cooke, P.H., Hicks, K.B., 2005. Encapsulation of essential oils in zein nanospherical particles. J. Agric. Food Chem. 53, 4788e4792. Shimada, M., Mochizuki, K., Goda, T., 2009. Feeding rats dietary resistant starch shifts the peak of SGLT1 gene expression and histone H3 acetylation on the gene from the upper jejunum toward the ileum. J. Agric. Food Chem. 57, 8049e 8055. Tester, R.F., Morrison, W.R., 1990. Swelling and gelatinization of cereal starches. I.Effects of amylopectin, amylose, and lipids. Cereal Chem. 67, 551e557. Venkatachalam, M., Kushnick, M.R., Zhang, G., Hamaker, B.R., 2009. Starchentrapped biopolymer microspheres as a novel approach to vary blood glucose profiles. J. Am. Coll. Nutr. 28, 583e590. Wachters-Hagedoorn, R.E., Priebe, M.G., Heimweg, J.A.J., Heiner, A.M., Englyst, K.N., Holst, J.J., Stellaard, F., Vonk, R.J., 2006. The rate of intestinal glucose absorption is correlated with plasma glucose-dependent insulinotropic polypeptide concentrations in healthy men. J. Nutr. 136, 1511e1516. Woodward, A.D., Regmi, P.R., Ganzle, M.G., van Kempen, T.A., Zijlstra, R.T., 2012. Slowly digestible starch influences mRNA abundance of glucose and shortchain fatty acid transporters in the porcine distal intestinal tract. J. Anim. Sci. 90 (Suppl. 4), 80e82. Xu, H., Chai, Y., Zhang, G., 2012. Synergistic effect of oleic acid and glycerol on zein film plasticization. J. Agric. Food Chem. 60, 10075e10081. Zhang, G., Ao, Z., Hamaker, B.R., 2006a. Slow digestion property of native cereal starches. Biomacromolecules 7, 3252e3258. Zhang, G., Ao, Z., Hamaker, B.R., 2008. Nutritional property of endosperm starches from maize mutants: a parabolic relationship between slowly digestible starch and amylopectin fine structure. J. Agric. Food Chem. 56, 4686e4694. Zhang, G., Maladen, M., Campanella, O.H., Hamaker, B.R., 2010. Free fatty acids electronically bridge the self-assembly of a three-component nanocomplex consisting of amylose, protein, and free fatty acids. J. Agric. Food Chem. 58, 9164e9170. Zhang, G., Venkatachalam, M., Hamaker, B.R., 2006b. Structural basis for the slow digestion property of native cereal starches. Biomacromolecules 7, 3259e3266.

Please cite this article in press as: Xu, H., Zhang, G., Slow digestion property of microencapsulated normal corn starch, Journal of Cereal Science (2014), http://dx.doi.org/10.1016/j.jcs.2014.01.021