Resistant starch: A review of analytical protocols for determining resistant starch and of factors affecting the resistant starch content of foods

Food Research International 43 (2010) 1959–1974

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Food Research International j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / f o o d r e s

Review

Resistant starch: A review of analytical protocols for determining resistant starch and of factors affecting the resistant starch content of foods A. Perera a,⁎, V. Meda a, R.T. Tyler b a b

Department of Agricultural and Bioresource Engineering, University of Saskatchewan, Canada Department of Food and Bioproduct Sciences, University of Saskatchewan, Canada

a r t i c l e

i n f o

Article history: Received 8 March 2010 Accepted 8 June 2010 Keywords: Resistant starch Starch digestibility Starch determination Starch hydrolysis

a b s t r a c t Resistant starch (RS) has drawn considerable attention over the last two decades due to its demonstrated and putative positive impacts on health. This has resulted in the development of a variety of analytical protocols for its determination, hence a comprehensive review of methodologies for analyzing resistant starch is warranted. Adding to the complexity, the RS contents of starchy materials vary widely and RS levels are impacted by processing. This review compares commonly used methods for the determination of RS, briefly reviews the process of starch digestion in the human, and discusses the complications and challenges associated with determining RS in foods. © 2010 Elsevier Ltd. All rights reserved.

Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2. Starch digestion in the human . . . . . . . . . . . . . . . 3. Demonstrated and putative health benefits of RS consumption 4. The rat as a model for starch digestion in humans . . . . . . 5. Methods of RS determination . . . . . . . . . . . . . . . . 6. Effect of starch composition on RS . . . . . . . . . . . . . 7. Effect of processing on RS levels . . . . . . . . . . . . . . 8. Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1. Introduction Polysaccharides in foods consist of starch and plant cell wall constituents. On the basis of its digestibility, starch was classified by Englyst and Cummings (1987a) into three groups, namely readily digestible starch, partially resistant starch and resistant starch. According to this classification, starch that is not accessible to digestive enzymes, such as that protected by hard to digest coatings in whole and coarsely-milled grains, starch in raw banana and potato exhibiting B- or C-type X-ray diffraction patterns, and retrograded amylopectin, is considered to be partially resistant starch. Retrograded amylose that can be solubilized in potassium hydroxide and which subsequently becomes

⁎ Corresponding author. Tel.: + 1 306 966 2454. E-mail address: [email protected] (A. Perera). 0963-9969/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2010.06.003

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susceptible to hydrolysis by amyloglucosidase is referred to as resistant starch (RS). This definition of RS was modified later to include ‘the sum of starch and starch-degradation products that, on average, reach the human large intestine’ (Englyst, Kingman, Hudson, & Cummings, 1996). Partially resistant starch and RS as defined by Englyst and Cummings (1987a) were subsequently reclassified as RS type 1, RS type 2 and RS type 3 (Englyst, Kingman, & Cummings, 1992; Sajilatha, Singhal, & Kulkarni, 2006). Enzyme inaccessible starch resulting from structural rigidity is defined as RS1, and it is calculated as the difference between the enzyme-extractable glucose contents of a food determined with and without an homogenization treatment prior to analysis (Sajilatha et al., 2006). Englyst et al. (1992) reported RS1 as the difference between the glucose contents of two samples of a food, one after a milling/ homogenization treatment to obtain 0.2-mm-sized particles and the other after a mincing treatment, and subsequent hydrolysis with pancreatin and amyloglucosidase for 120 min. It seems that Englyst et al. (1992) assumed that comminution (milling or homogenization) of

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foods would yield a consistency and particle size similar to that of mastication. However, this may not be true for all foods and RS1 values determined for comminuted samples may differ from those determined for otherwise identical masticated samples. For example, Åkerberg, Liljeberg, Granfeldt, Drews, and Björck (1998) evaluated RS in selected foods including RS1-rich raw banana. Foods were masticated (15 chews in 15 s) prior to analysis. Åkerberg, Liljeberg, Granfeldt, et al. (1998) reported RS values (72 g/100 g starch) that were higher than those reported (53.6 g/100 g starch) by Englyst and Cummings (1986). The latter group employed the analytical method of Englyst, Wiggins, and Cummings (1982) where samples were ball-milled. Starch granules in raw foods which are resistant to digestion comprise RS2. Analytically, RS2 is measured as the difference in the amount of glucose liberated by pancreatin and amyloglucosidase, after 120 min of hydrolysis, from two samples of the same food (having the same particle size), one having been subjected to a prior boiling treatment and one not. Retrograded starch formed during the cooling of gelatinized starch is termed RS3 (Englyst et al., 1992). Based on the definitions above, it is clear that the RS1, RS2 and RS3 contents determined for a particular food sample may be affected by differences in sample processing (mastication, homogenization, grinding, etc.). Cross-linking of starches from wheat, corn, rice, potato, tapioca, mung bean and oat, using sodium trimetaphosphate (STMP), sodium tripolyphospahate (STPP), epichlorohydrin or phosphoryl chloride (POCl3), produced starch resistant to α-amylase hydrolysis, which was termed RS4 (Seib & Woo, 1999). These authors demonstrated that RS levels in wheat starch cross-linked with 12% STMP/STPP, 2% POCl3 and 2% epichlorohydrin were 75.6, 85.6 and 75.8 g/100 g starch, respectively. Other chemically-modified starches, e.g. starch etherified with propylene oxide or cross-linked with phosphorous oxychloride, acid-modified starch and starch oxidized with sodium hypochlorite, also have been reported to be resistant to in vitro hydrolysis by α-amylase and amyloglucosidase (Wolf, Bauer, & Fahey, 1999). The classification of starch has been expanded to include rapidly digestible starch (RDS) and slowly digestible starch (SDS) in addition to RS. Starch that is hydrolyzed in vitro within 20 min with αamylase and amyloglucosidase is designated RDS (Englyst, Veenstra, & Hudson, 1996). The category of SDS includes enzyme inaccessible starch and raw starch that is fully hydrolyzed in vitro during prolonged incubation (20–120 min) (Englyst et al., 1992; Sajilatha et al., 2006). Starch that is not hydrolysed after 120 min incubation with pancreatin and amyloglucosidase is termed RS (Englyst et al., 1992). 2. Starch digestion in the human As described above, the concept of RS is based on the inability of digestive enzymes to hydrolyze some physical and chemical forms of starch in foods in vivo or in vitro. Therefore, it is useful to review the process of starch digestion in humans. Fig. 1 summarizes the major organs that participate in the digestion of foods and the enzymes secreted. Salivary glands that open into the oral cavity produce several enzymes that initiate carbohydrate digestion, e.g. α-amylase, glycosidases, glucose oxidase, lactate dehydrogenase and β-glucuronidase (Makinen, 1989). Food masticated and partially hydrolyzed in the mouth passes through the pharynx and then through the esophagus and into the stomach. Submucosal glands of the esophagus secrete bicarbonates and mucin. This is considered a mechanism to protect the esophagus from HCl refluxed from the stomach (AbdulnourNakhoul et al., 2005). In the stomach, food is mixed with pepsin, gastric lipase and HCl, which activates pepsin. No significant digestion of starch takes place in the stomach but contraction of muscles facilitates comminution of foods (Correa, 1988). Food that is passed into the small intestine is termed ‘chyme’ and there it is mixed with bicarbonates and mucin secreted by the Brunner's glands of the small intestine (DeSesso & Jacobson, 2001). In the duodenum, the first part of the small intestine, chyme is blended with bile secreted by the gallbladder, pancreatic α-amylase, and amylolytic and other enzymes secreted by

the epithelial cells of the small intestine, such as enterokinase, sucrase, maltase and lactase. These enzymes are responsible for the hydrolysis of carbohydrates into monosaccharides. In addition, proteolytic enzymes such as trypsin, chymotrypsin, carboxypeptidase and elastase, lipolytic enzymes such as lipase, phospholipase and cholesterol esterase, and the DNA and RNA hydrolyzing enzymes ribonuclease and deoxyribonuclease are secreted by the pancreas and mixed with the chyme (Cichoke, 1998; DeSesso & Jacobson, 2001). Chyme that is not hydrolyzed into absorbable molecules in the small intestine, e.g. starch which has escaped digestion, along with non-starch polysaccharides, moves into the colon and undergoes bacterial fermentation. The resulting shortchain fatty acids are absorbed in the colon and provide 5–10% of the energy requirement of humans (Nordgaard & Mortensen, 1995). It has been shown that of the total quantity of starch consumed by ileostomy subjects, approximately 3% of freshly cooked starch and approximately 12% of cooked and cooled starch escape digestion in the small intestine and can be recovered in the ileum. All of the RS and the non-starch polysaccharides in the diet were found in the ileum effluent of tested subjects (Englyst & Cummings, 1985, 1987b). Approximately 80–90% of the RS that passes into the human colon is fermented and the remainder is released with the feces. Individual variations in the microbial population of the colon can influence significantly the degree of RS fermentation. The presence of RS in the diet decreases considerably the bacterial fermentation of non-starch polysaccharides, which is useful as non-starch polysaccharides increase the bulk of the excreta and improve its water holding capacity (Cummings, Beatty, Kingman, Bingham, & Englyst, 1996). 3. Demonstrated and putative health benefits of RS consumption RS is recognized as a significant contributor to gastrointestinal health. Undigested starch is fermented by microorganisms in the large bowel to produce short chain fatty acids, including acetate, propionate and butyrate (Bird, Brown, & Topping, 2000; Brouns, Kettlitz, & Arrigoni, 2002; Wong, de Souza, Kendall, Emam, & Jenkins, 2006) and isobutyrate, valerate and isovalerate (Hylla et al., 1998). A high-amylose corn starch diet containing 46–50% of RS2 significantly increased the colonic production of acetate, propionate and butyrate in rats. This diet also increased apoptosis in the colon subsequent to externally induced gene damage, which suggests an ability of RS to control the initiation of colonic cancer (Leu, Hu, Brown, & Young, 2009). Butyrate was reported to increase the level of glutathione, an antioxidant, in colonic mucosa, improving colonic resistance to toxic agents in the diet (Hamer et al., 2009). A significant decrease in bile acids (cholic acid, chenodeoxycholic acid, deoxycholic acid, lithocholic acid, isolithocholic acid and ursodeoxycholic acid) and total neutral sterols (coprostanol, cholesterol, 4cholesten-3-one, campesterol, stigmasterol and β-sitosterol) in the fecal matter of healthy adults was reported after consuming experimental foods rich in RS for 4 weeks (Hylla et al., 1998). As the fecal matter of colon cancer patients carries more bile acids and neutral steroids than does that of healthy controls (Reddy, Ernst, & Wynderm, 1977), it is believed that RS has a positive effect on the control and prevention of colon cancer. Significant expression of a ‘cell cycle regulatory and cell proliferation gene’ was observed in colorectal cancer patients after their consumption of 40 g/day of RS for 2–4 weeks. The expression of the gene was inhibited in control subjects (Dronamraju, Coxhead, Kelly, & Mathers, 2007). Consumption of RS has other benefits. A diet rich in dietary fibre and RS was reported to significantly increase the weight of the pancreas, liver and intestine, and the length of the intestine, in rats (Correa, Angelina, Reis, Maria, & de Oliveira Costa, 2009). RS was reported to decrease the postprandial blood glucose level considerably within the first 120 min (Kendall et al., 2008). Compared to a diet containing autoclaved and cooled starch from waxy barley (which would not undergo significant retrogradation), significantly lower levels of blood glucose (within the first 120 min) were reported after feeding

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Fig. 1. Enzymes secreted by major organs participating in the digestion of foods in humans. The digestive system, an extension of the environment into the body, also secretes mucus, acid, bicarbonate and salts to facilitate hydrolysis of foods and absorption of nutrients essential for life.

retrograded high-amylose barley (∼18% RS) to rats (Xue, Newman, & Newman, 1996). RS3 in the diet has a laxative effect. A supplement of 25 g/day in healthy test subjects increased the daily fecal output above the normal level with minimal gastrointestinal discomfort (Maki et al., 2009). A RS-rich green banana diet had beneficial effects on controlling shigellosis in child patients by decreasing stool volume, number of stools per day and red blood cells in stools, and increasing levels of acetate, propionate and butyrate in feces. Despite the expected negative impact of antibacterial treatments (ciprofloxacin) on short chain fatty acid production in the colon, acetate, propionate and butyrate production in child patients increased on the fifth day of feeding green banana (Rabbani et al., 2009). A RS-supplemented diet significantly increased populations of lactobacilli, bifidobacteria, staphylococci and streptococci, decreased the enterobacteria population, and altered microbial enzyme metabolism in the colon of experimental rats (Silvi, Rumney, Cresci, & Rowland, 1999). For a balanced view of the effect on RS on health, it is important to note that the consumption of high amounts of RS may have some negative effects on gastrointestinal performance. These include bloating, borborygmi (noise due to gas movement in the intestine), flatulence, colic and watery feces (Storey, Lee, Bornet, & Brouns,

2007). Consumption of common bean (Phaseolus vulgaris L.) rich in RS (12–13 g/100 g raw starch) and soluble dietary fibre introduced flatulence, bloating, abdominal noise and pain in test subjects, but symptoms significantly decreased when fermented beans were consumed (Granito, Michel, Frías, Champ, & Guerra, 2005). In a review, Grabitske and Slavin (2009) explained that diarrhea is an extreme outcome of ingesting carbohydrates with very low digestibility, including RS, when the capacity of colonic fermentation is exceeded by consumption. They also noted that adverse effects are more prominent with RS3 than with RS2, and that the severity of symptoms differed with personal attributes such as age, weight, gender, genetics, health and the composition of the gut microflora. Overall, the benefits of RS consumption were considered to outweigh any gastrointestinal discomfort. 4. The rat as a model for starch digestion in humans As described above, animal models have been used in some RS research studies and thus it is important to discuss briefly the dependability and/or applicability of the results obtained. Animal models used in biomedical research should be either analogous or

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homologous to humans considering the anatomy and physiology of the organ or system under investigation. Other criteria include, but are not limited to, the selected animal should be easily available in substantial numbers, should be easy to handle and manageable with the resources available, and the life span should be sufficiently long to carry out the research. In keeping with these criteria, omnivores such as the rat and the pig are used to simulate the gastrointestinal tract and liver functions of the human (Chow, 2008). In a comprehensive review, DeSesso and Jacobson (2001) compared the similarities and differences between the gastrointestinal tracts of the human and the rat. Some significant differences are listed here. The human pharynx is a single tube that is the passageway for both food and air, whereas the rat pharynx is separated into two compartments for respiratory and digestive purposes. The human stomach is a single chamber where food is mixed with enzymes and acid. The rat stomach, although a single chamber, is functionally divided into two areas. The forestomach is the site of bacterial digestion, whereas the glandular stomach secretes enzymes and acid. Bacterial digestion is absent in the human stomach. Although the rat is used to imitate digestion in the human, there is the likelihood of species differences in enzyme activity. The small intestine has three functionally different regions, the duodenum, the jejunum and the ileum. Compared to the human, where the gallbladder secretes bile, the rat liver secretes twice as much as bile into the duodenum per kg of body weight per day. Nutrient absorption takes place in the duodenum and the forejejunum of both rats and humans through diffusion, active transport and solvent drag mechanisms. Compared to the total length of the digestive tract, the jejunum of the rat is proportionally longer than that of the human. The jejunum of the rat represents 90% of the length of the small intestine, and that of the human, 38%. The transit time of food through the rat small intestine is slower than that in the human. Despite the human small intestine being 5.5 times longer than that of the rat, the transit time of food through the small intestine of the human and the rat is similar, 3–4 h. The surface area of the human small intestine is 200 times greater than that of the rat, which is significant given the difference in their lengths. Water and nutrients formed through bacterial metabolism are absorbed in the large intestine. The human large intestine is divided into the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anus. The sigmoid colon is absent in the rat. The cecum is responsible for most of the microbial digestion of food in the rat and represents up to 26% of the length of the large intestine. In contrast, the human cecum is only 5% of the length of the large intestine. In addition, the types of microorganisms naturally occurring in the digestive systems of the human and the rat may be different (DeSesso & Jacobson, 2001). The differences described above indicate that the rat model may not provide reliable data on RS digestion in humans, but it may be useful in understanding the fate of RS within the digestive tract.

5. Methods of RS determination Determination of RS in food ingredients and processed foods has become vital to the provision of nutritional information to consumers and others. To enable effective use of the research output on RS for food processing and nutritional applications, analytical procedures for the determination of RS need to be compared. At present, significant differences exist among procedures with respect to sample preparation, the enzymes used, and the establishment of experimental conditions that mimic gastrointestinal digestion of starch. Ongoing improvements in analytical methodology are essential, but frequent modifications in protocols reduce the availability of comparable data to assess the efficacy of methods and the nutritional quality of foods. Added to this, food analytes used in the various procedures have differed in their genetic origin, composition and processing history. This paper reviews

current methods of analysis of RS and difficulties related to comparing data generated by different methods. In vitro methods for the analysis of RS in foods are based conceptually on the gastrointestinal digestion of starch in foods. Enzyme hydrolysis is a common feature of all methods, combined with chemical hydrolysis or gravimetric isolation. Differences in sample preparation are significant and range from mechanical methods (milling, grinding and homogenization) to mastication. The type of RS quantified is dependant on the protocol. Most methods are focused on the determination of total RS, but specific methods have been developed to quantify RS1, RS2 and RS3. Methods for the determination of RS proposed by Englyst et al. (1982) and Englyst et al. (1992) are the basis for this discussion. Significant modifications proposed by other authors are compared and contrasted. As proposed by Englyst et al. (1982), RS and other nonstarch polysaccharides are first separated from the enzyme-hydrolyzable starch. Then, RS is solubilized in alkali and thereby separated from the other enzyme resistant polysaccharides. Even though Englyst et al. (1982) labelled this fraction as RS, the analytical protocol used reveals that it measures RS3 only. Briefly, in this method (Fig. 2) 100–200 mg of homogenized wet sample or ground dry sample is mixed with sodium acetate buffer at pH 5.4 and heated for 1 h at 100 °C to gelatinize starch. Having included homogenization and boiling steps, this protocol eliminates the contribution of RS1 and RS2 to the final RS value. An enzyme mixture containing α-amylase, pullulanase and amyloglucosidase is added and hydrolysis is carried out for 16 h at 40 °C. Absolute ethanol is added to terminate enzyme activity and to precipitate nonhydrolyzed starch. The pellet is collected after centrifugation and washed twice with 80% ethanol. The residue is dried with acetone and then treated with 2 M potassium hydroxide for 30 min at room temperature to solubilize retrograded starch (RS3). An aliquot of alkali digest is mixed with 2 M acetic acid and amyloglucosidase and the contents are incubated at 65 °C for 1 h. After cooling and centrifuging, neutral sugars (glucose, galactose, mannose, xylose and arabinose) in the supernatant are analyzed by gas–liquid chromatography (GLC). The quantity of glucose detected by GLC represents the amount of RS (RS3) in the sample. The above procedure was modified later by the authors (Englyst et al., 1992) to measure total glucose, free glucose, total RS, and RS1, RS2 and RS3 as separate fractions. The determination of total RS is carried out in step-wise fashion. Total glucose (TG) and free glucose (FG) contents are determined, as explained in Fig. 3.1, in order that total starch (TS) may be calculated as TS= (TG − FG) × 0.9. In this protocol for TS determination, RS1 and RS2 are eliminated by mincing/milling/ homogenizing the food sample and subsequently heating the sample at 100 °C for 30 min, respectively. Any retrograded starch that contributes to RS3 is eliminated by treating the sample with 7 M potassium hydroxide at 0 °C. The rapidly digestible starch (RDS) and slowly digestible starch (SDS) contents of the sample are determined separately and total RS is calculated as RS = TS − (RDS + SDS) (Fig. 3.2). In this method, 0.8–4.0 g of sample is minced only to minimize structural changes. The low viscosity of samples leads to the release of considerably higher amounts of glucose during enzyme hydrolysis, especially in the absence of other polysaccharides, than is the case with the in vivo digestion of starch. Thus, guar gum is added to increase the viscosity. Glass beads are added to samples to ensure proper mixing and to break cell walls during enzyme hydrolysis. For the determination of RDS and SDS, samples are equilibrated with 20 mL of acetate buffer at 37 °C and then starch is hydrolyzed with an enzyme mix containing pancreatin as a source of α-amylase (30,000 BPU/g), amyloglucosidase (400 AGU/mL), and invertase. (3000 EU/mL). Englyst et al. (1992) proposed that enzyme hydrolysis be carried out at 37 °C instead of at 40 °C, as previously used in the Englyst et al. (1982) protocol, to better mimic human physiological conditions of digestion. A significant reduction in the duration of enzyme digestion is used in the Englyst et al. (1992) protocol. Instead of 16 h of sample digestion with

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Fig. 2. Main steps in the Englyst et al. (1982) protocol for the determination of enzyme resistant starch (RS3). The presence of an enzyme resistant fraction of starch in foods was first observed by the authors during the measurement of non-starch polysaccharides in foods.

pancreatin, as per Englyst et al. (1982), the Englyst et al. (1992) protocol uses sequential removal of aliquots of enzyme digest at 20 min (as the rapid release of sugars ended at 20 min of digestion with pancreatin) and at 120 min from the beginning of the digestion. The rationale to terminate enzyme hydrolysis at 120 min is that the release of glucose reached a plateau at 120 min. The glucose content of the 20-min enzyme digest (G20 fraction) represents RDS and is calculated as RDS= (G20 − FG) × 0.9. The difference in glucose contents between the 120min and 20-min digests represents SDS and is calculated as SDS = (G120 − G20 − FG)× 0.9. Instead of directly measuring glucose originating from RS as in Englyst et al. (1982), this method indirectly estimates total RS as RS = TS− (RDS + SDS). As 37 °C is the highest temperature at which a sample is treated in this protocol, any RS2 in the food sample would not be hydrolyzed by α-amylase. RS1 also is preserved in the unhydrolyzed fraction as the sample is only minced and no milling or homogenization is employed. As a result, this indirect measurement of RS includes any RS1, RS2 and RS3 in the sample. Englyst et al. (1992) devised protocols for determination of RS1, RS2 and RS3. By definition, RS1 is the fraction of starch that is inaccessible to enzymes due to physical impediments, e.g. large-sized particles and cell walls. The analytical procedure for RS1 determination (Fig. 3.3a) differs from that of Englyst et al. (1982) (Fig. 2) with respect to the method of reduction of particle size. One portion of the sample (A) is minced once and the other portion (B) is either milled or homogenized, as appropriate, to obtain particles b 0.2 mm in diameter. Then, using the protocol for the determination of RDS and SDS (Fig. 3.2), glucose released after 120 min of enzyme hydrolysis (G120) is determined for each portion. RS1 is calculated as RS1 = [G120 (B) − G120(A)] × 0.9. Starch in raw foods and foods cooked with little water (preventing complete gelatinization of starch) contribute to RS2. The method for the determination of RS2 (Fig. 3.3b) compares the amount of glucose released enzymatically from a cooked sample to that from a raw sample (Englyst et al., 1992). One portion (C) of a raw food sample is heated in 0.1 M sodium acetate buffer, pH 5.2, in a boiling water bath for 30 min, while another portion (D) is used directly without a heat treatment. The samples are hydrolysed with amylase, amyloglucosidase and invertase and the glucose released

after 120 min (SDS) is determined using the procedure outlined in Fig. 3.2. RS2 is calculated as RS2 = [G120(C) − G120(D)] × 0.9. Determination of RS3 is limited to samples containing retrograded starch (Englyst et al., 1992) and the protocol is similar to that of Englyst et al. (1982) in many ways. In contrast to the protocol for the determination of RDS and SDS for the estimation of total RS (Fig. 3.2), where α-amylase, amyloglucosidase and invertase are used, the protocol for RS3 determination uses α-amylase and pullulanase at 40 °C. After removing the enzyme-hydrolyzable starch from the sample, retrograded starch is solubilized in 4 M potassium hydroxide at room temperature, whereas Englyst et al. (1982) used 2 M potassium hydroxide. However, this concentration is lower than that used (7 M) in the protocol for the determination of TG outlined in Fig. 3.1. The temperature at which retrograded starch is solubilized in potassium hydroxide also is different in the two procedures; 0 °C for TG and room temperature for RS3 determination (Englyst et al., 1992). Goñi, García-Diza, Mańasb, and Saura-Calixto (1996) cautioned about the possible effect of sample preparation in RS protocols as drying, cooling and conditions of storage can alter the level of RS in foods. Their method of RS determination is summarized in Fig. 4. In this procedure, a 100-mg sample is milled or homogenized before use and by doing so RS1 is eliminated. Sample pH is decreased to 1.5 with HCl–KCl buffer to simulate gastric pH. As a major modification to the procedure of Englyst et al. (1992), hydrolysis with pepsin at 40 °C for 1 h is introduced. Sample pH is adjusted to 6.9 with tris–maleate buffer to simulate conditions in the small intestine. Instead of using a cocktail of enzymes as in Englyst et al. (1992), samples are hydrolysed with α-amylase only for 16 h at 37 °C. As this method is focused on the determination of RS (not SDS and RDS), products from enzyme hydrolysis are discarded at this point. As 40 °C is the highest temperature to which the sample is exposed, any RS2 in raw foods is included in the unhydrolyzed fraction. The pellet is dispersed in 4 M potassium hydroxide at room temperature for 30 min to solubilize RS3. Dextrin in the alkali digest is hydrolyzed to glucose with amyloglucosidase at 60 °C for 45 min. Glucose content is determined using a colorimetric assay. Based on the analytical procedure of Goñi et al. (1996), the presumed definition for RS is starch that is not

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Fig. 3.1. Summary of the protocol for the determination of total starch (TS) as per Englyst et al. (1992). The free glucose (FG) and total glucose (TG) contents are measured to estimate the total starch content of the sample.

hydrolyzed by α-amylase within 16 h at body temperature, which is in contrast to the Englyst et al. (1992) definition where RS is starch that is not hydrolyzed by pancreatin, amyloglucosidase and invertase within 120 min. Other modifications to the Englyst et al. (1992) method have been proposed but the essence of the method (to remove hydrolyzable starch with enzymes) remained unchanged. Chung, Lim, and Lim (2006) modified the Englyst et al. (1992) protocol to eliminate redundancy and to introduce a reduction in sample size (to 0.5 g). Instead of adding guar gum separately to each sample tube with subsequent dissolution in acetate buffer, Chung et al. (2006) prepared a solution of guar gum in HCl (to increase its solubility) and then added aliquots to each sample. The volume of sodium acetate is decreased to 5 mL by increasing its molar concentration to 0.5 M (20 mL of 0.1 M sodium acetate is used in the Englyst et al. (1992) protocol). Chung et al. (2006) deleted invertase from the enzyme mix. The digests collected (0.5 mL) after 20 and 120 min were mixed with 4 mL of 80% ethanol, which replaced the 20 mL of 66% ethanol in the Englyst et al. (1992) protocol. RS was calculated as the difference between total starch and starch not hydrolysed at 120 min as in Englyst et al. (1992). The Megazyme® kit for RS determination is widely used in analytical laboratories and is the basis of both AOAC method 2002.02 and AACC Method 32–40 (Megazyme, 2008). The procedure is summarized in Fig. 5. This method, in many ways, is similar to that of Englyst et al. (1982). Samples are ground to pass a 1-mm sieve which generates a coarse meal, thus RS1 is accounted for in this method. The Megazyme® protocol eliminates the initial boiling of samples in acetate buffer and the use of pullulanase. Instead, it

employs a mixture of α-amylase (3 Ceralpha Units/mg) and amyloglucosidase (3300 U/mL) to hydrolyze starch in raw or processed food samples. Hydrolysis is carried out for 16 h at 37 °C as proposed by Englyst et al. (1982). As a result, RS2 in raw foods would not be hydrolyzed during this procedure. After inactivation of enzymes with 99% ethanol, glucose in the sample is removed by two washings with 50% ethanol. Similar to Englyst et al. (1982), the pellet collected from digestion is treated with 2 M potassium hydroxide to extract RS3 from the fibre-rich matrix. Dextrins thus produced are hydrolyzed to glucose with amyloglucosidase. The incubation time with amyloglucosidase is reduced to 30 min at 50 °C (Megazyme, 2008) from 1 h at 65 °C (Englyst et al., 1982). The Megazyme® method uses the glucose oxidase-peroxidase colorimetric assay to determine the glucose concentration in the final hydrolysate, as did Englyst et al. (1992). The Megazyme® protocol for RS does not enable the determination of SDS and RDS. Eerlingen, Crombez, and Delcour (1993) proposed enzymaticgravimetric isolation of RS from wheat starch pre-gelatinized at 121 °C and subsequently stored at 0, 68 and 100 °C. In this method, samples are placed in boiling phosphate buffer, pH 6, and hydrolyzed with Termamyl® (heat stable α-amylase) at 100 °C for 30 min. After cooling to room temperature, the pH is adjusted to 4.5 with 2% phosphoric acid. Samples are hydrolyzed with amyloglucosidase at 60 °C for 30 min and then centrifuged. The pellet is washed with deionized water, dispersed in phosphate buffer at pH 7.5 and incubated with protease at 42 °C for 4 h. The residue after digestion is collected by filtration and oven-dried at 80 °C. The weight of the enzyme-insoluble residue represents the RS content of the starch

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Fig. 3.2. Englyst et al. (1992) protocol for the determination of rapidly digestible starch (RDS) and slowly digestible starch (SDS) as the preliminary step in the estimation of RS in a food sample. The procedure for the estimation of total starch (TS) is explained in Fig. 3.1.

sample. Faraj, Vasanthan, and Hoover (2004) also isolated RS gravimetrically, but introduced a preliminary hydrolysis with lichinase and β-glucosidase. Then, samples are treated with a fungal protease at 42 °C, Termamyl® at 100 °C and amyloglucosidase at 50 °C, respectively. RS is collected by drying the enzyme resistant residue. It is important to note that the gravimetric separation of RS is acceptable only for analytes free of non-starch polysaccharides. Other modifications have been made to the sample preparation step of RS determination with the intent of more closely simulating in vivo digestion. Åkerberg, Liljeberg, Granfeldt, et al. (1998) and Åkerberg, Liljeberg, and Björck (1998) employed chewing of food samples to initiate hydrolysis by salivary amylase. According to these authors, the number of times a food sample is chewed has a significant effect on the end result. Briefly, the chewed food sample (15 chews in 15 s) and subsequent mouth wash are expectorated into a beaker containing pepsin in Na/K phosphate buffer. Then, the pH is adjusted to 1.5 with HCl and the sample is incubated for 30 min at 37 °C to simulate gastric conditions. Sample pH then is adjusted to 5 with sodium acetate buffer (0.5 M, pH 5) and sodium hydroxide. Subsequently, starch hydrolysis is carried out with a mixture containing MgCl2, CaCl2, 2-propanol, pancreatin and amyloglucosidase for 16 h at 40 °C. Then, 95% ethanol at 60 °C is added in excess, leading to the formation of a precipitate at room temperature. The precipitate, collected by filtration, is dehydrated with 95% and 99% ethanol and solubilized in 2 M potassium hydroxide. The total starch content of the alkali digest is determined and expressed as RS. Muir and O'Dea (1992) also employed chewing for sample preparation.

Sample pH is then adjusted to 2 and the sample is hydrolysed with pepsin for 30 min at 37 °C. After neutralizing the pH with sodium hydroxide, pancreatin and amyloglucosidase are added to samples in acetate buffer at pH 5 and incubated for 6 h at 37 °C. According to the authors, this reduction in hydrolysis time (6 h instead of 16 h) is intended to represent better the movement of food through the small intestine. The Muir and O'Dea (1992) protocol significantly deviates from the approaches already discussed as the pellet collected after pancreatin hydrolysis (at 37 °C) is further treated with thermostable α-amylase (Termamyl) at 100 °C, presumably to hydrolyse RS2. The pellet recovered after Termamyl hydrolysis is boiled with dimethyl sulfoxide (DMSO) for 1 h. The supernatant from Termamyl hydrolysis (RS2) and the digest from DMSO treatment (RS3) are mixed and the glucose content of the mixture is determined. Introduction of DMSO in lieu of potassium hydroxide for solubilization of RS3 is a novel feature of the Muir and O'Dea (1992) protocol. Saura-Calixto, Goňi, Bravo, and Maňas (1993) determined RS in dietary fibre. Instead of using pancreatin as the source of α-amylase, they used heat stable αamylase at 100 °C to eliminate traces of starch. The pellet from enzyme digestion is sequentially hydrolyzed using a protease and amyloglucosidase for 35 min at 60 °C. The residue is collected and dehydrated with ethanol and acetone, and subsequently dispersed in 2 M potassium hydroxide at room temperature. After adjusting the pH to 4.75 with acetate buffer, dextrins in the solution are hydrolyzed with amyloglucosidase at 60 °C for 35 min. The glucose oxidaseperoxidase system is used to measure glucose in the supernatant collected after centrifugation.

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Fig. 4. Goñi et al. (1996) protocol for the determination of resistant starch (RS) in foods.

It is important to note that very little information is available on the in vivo digestibility of foods for which in vitro RS data is available. From a nutritional point of view, this is a drawback. Grinding and homogenization would certainly produce food particles much smaller than those resulting from chewing. Englyst et al. (1992) compared chewing of samples against mincing and reported that differences in results were more related to the source of starch than to the method of mincing. Individuals differ in their chewing habits and may not chew the same number of times as in an experimental procedure. Therefore, available RS1 may vary from person to person as its level depends on particle size. It is important to consider possible variability in RS data associated with the technique employed to sample the enzyme hydrolysate, because the colorimetric glucose assay is sensitive to inaccuracies in sample volume. Englyst et al. (1992) proposed drawing of 0.5-mL volumes of the hydrolyzate after 20 and 120 min to determine RDS and SDS, respectively. Then, RS is computed as the difference between total starch and enzyme-hydrolyzed starch. Chung, Liu, and Hoover (2009) reduced the volume of sample drawn to 0.1 mL. It has been observed that undigested food particles interfere with pipetting (especially at the 20-min sampling point) more frequently than one might expect. This would significantly influence the reproducibility of the colorimetric assay of glucose. The advantage of using gas–liquid chromatography to measure glucose is such errors can be corrected by using an internal standard, as did Englyst et al. (1982). In this connection, the Megazyme® protocol eliminated variability related to sample volume by employing the total volume of the digest after potassium hydroxide treatment for centrifugation and then drawing

an aliquot for color development. The availability of RS controls from Megazyme® is useful for understanding experimental errors. It is reasonable to expect that variations in analytical procedures, including differences in the enzymes used and in their concentration and sequence of application, and dissimilarities in the conditions of experiments, would significantly alter the levels of RS detected in similar foods. RS values of selected foods as reported by some authors (Åkerberg, Liljeberg, & Björck, 1998; Chung et al., 2006; Englyst et al., 1992; Faraj et al., 2004; Muir & O'Dea, 1992; Szczodrak & Pomeranz, 1991; Tribess et al., 2009) are presented in Table 1. Englyst and Hudson (1996) reported RS values of a large number of different food items, but the non-availability of information on handling and storage pre- and post-processing prevent any useful comparison. The analysis of resistant starch in Englyst et al. (1982) is limited to a few sources including white bread, whole wheat bread and corn flakes (0.8%, 0.8% and 2.9% RS, respectively, on a dry weight basis) because the main focus of this study was to propose a method to determine non-starch polysaccharides in foods, not RS. 6. Effect of starch composition on RS Amylose and amylopectin are the two major polysaccharides in starch, both having glucose as the fundamental building block. Linear chains of glucose in both amylose and amylopectin are linked through α (1→ 4) bonds. Amylopectin is heavily branched and chains are linked through α (1→ 6) bonds to form a complex structure. Amylose shows a low degree of branching (Bertoft, 2004). Conventionally, amylose in starch is recognized by the deep blue color of the complex formed with

Fig. 3.3. Summary of protocols for the determination of RS1 (a) and RS2 (b) according to Englyst et al. (1992). RS1 represents the fraction of starch inaccessible to enzymes due to large particle sizes. RS2 represents the enzyme resistant starch in raw foods.

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Fig. 5. Summary of the Megazyme method of determination of resistant starch (RS) (Megazyme, 2008).

I2. In this structure, poly-iodine occupies the interior of the amylose helix consisting of six glucose units per turn and in almost circular crosssection (Rundle, 1947). A steady blue color (at 570 nm) corresponds to a degree of polymerization (DP) ≥ 45 or a helix with 7–8 turns. Amylose chains with 12 b DPb 45 produce a range of colors from red to purple, respectively (Bailey & Whelan, 1961). In the amylopectin structure, areas where branching begins and those having only linear chains are clearly separated, producing amorphous and crystalline layers, respectively. It is believed that amylose is confined mostly to the amorphous layers (Donald, 2004). Two models are postulated for the biosynthesis of amylose. Debranching of pre-amylopectin to produce pre-amylose and subsequent elongation of glucan chains by granule bound starch synthase I (GBSSI) to form amylose is a widely accepted model. The other model proposes the synthesis of amylose through elongation of short chains of malto-oligosaccharides by GBSSI (Chibbar, Ganeshan, & Båga, 2007; Smith, 2001; van de Wal et al., 1998). German, Blumenfeld, Guenin, Yuryev, and Toistoguz (1992) demonstrated that gelatinized amylose aggregates to form a gel network during cooling, whereas amylopectin acts as an agent of aggregation and a network filler. Hydrolysis of amylose gels is dependant on gel strength, since diffusion of α-amylase is decreased in strong gels that form resistant starch (Cairns, Sun, Morris, & Ring, 1995). The ratio of amylose to amylopectin, their chain lengths and the presence of lipid influence the degree of retrogradation of starch from cereals and pulses (Chung & Liu, 2009a). In lipid-rich starches, gelatinized amylose preferentially combines with lipid at a relatively high temperature (during cooling) before retrogradation begins and impedes retrogradation of the remainder of the amylose. On the other hand, small amounts of amylose-lipid complexes act as nucleation sites for amylose chains. During retrogradation, long chains of amylose in potato and amylopectin in amylomaize form weak associations at low temperatures (exothermic peak at ∼30 °C) perhaps due to the obstructions caused by branched chains (Chung & Liu, 2009a). Variations in the composition of cereal starch, in terms of

the amylose to amylopectin ratio, are governed by the genome and their genetic potential to undergo mutations (Rahman et al., 2007). For example, mutations in wheat that lead to null genes for GBSSI resulted in amylose-free endosperm starch (Vrinten & Nakamura, 2000). Similarly, inhibition of the expression of GBSSI in potato produced amylose-free starch. On the other hand, rice varieties high in GBSSI were reported to produce endosperm rich in amylose (Wang et al., 1995). Differences in the GBSSI gene have been observed to produce differences in the amylopectin levels in japonica and indica rice (Umemoto, Yano, Satoh, Shomura, & Nakamura, 2002). The influence of genetics on the RS contents of pulses is presented in Table 2. Three cultivars of pea, 1674-13, 1215-33 and 1329-12, contained different levels of RS when analyzed using the same protocol. Two cultivars of lentil, CDC Meteor and CDC Robin, had similar levels of RS (Chung, Liu, Hoover, Warkentin, & Vandenberg, 2008). Similarly, three cultivars of common bean, Majesty, Red Kannern and AC Nautica, had similar levels of RS (Chung et al., 2008). Significant differences in RS levels were observed among chickpea cultivars (Myles, FLIP 97-101C, 97-Indian2-11) (Chung, Liu, Donner, et al., 2008). Genotype-specific differences in the amylose and amylopectin ratios of sorghum and related differences in RS were reported. According to Sang, Bean, Seib, Pedersen, and Shi (2008), starch from heterowaxy sorghum (14% amylose) had the highest amount of RS (23.7%) compared to waxy sorghum starch (0% amylose; 8.4% RS) and normal sorghum starch (23.7% amylose; 17.9% RS), indicating the significance of the amylose to amylopectin ratio with respect to the RS level. In another study of four different hybrids, aeae × aeae (high amylose); fl1fl1 × fl1fl1; aeae (female) × fl1fl1 (native) and aeae (pollen) × fl1fl1 (female), starch from self pollinated aeae produced the highest amounts of RS (55.2%) compared to the other hybrids (1–6% RS) (Yao, Paez, & White, 2009). Genotypic variations influenced RS levels in thermally processed low- (23-Am), and highamylose (67-Am) pea (Pisum sativum L). Autoclaved (1.35 bar for 1 h)

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Table 1 Comparison of resistant starch contents of foods as determined by different methods. Food

RS

Description of hydrolysis

Author

White bread

Description

1% 2%

Englyst et al. (1992) Åkerberg, Liljeberg, and Björck (1998)

Wholemeal bread

1% 6%

Pancreatin, amyloglucosidase Chewing, pepsin, pancreatin, amyloglucosidase, MgCl2, CaCl2, 2-propanol Pancreatin, amyloglucosidase Chewing, pepsin, pancreatin, amyloglucosidase, MgCl2, CaCl2, 2-propanol Termamyl, protease, amyloglucosidase

Pancreatin, amyloglucosidase Pepsin, pancreatin, amyloglucosidase, Termamyl Pepsin, pancreatin, amyloglucosidase, Termamyl Pancreatin, amyloglucosidase Pancreatin, amyloglucosidase Lichinase, β-glucosidase, fungal protease, Termamyl, amyloglucosidase Heat stable α amylase, amyloglucosidase Heat stable α amylase Amyloglucosidase, pepsin and amylase (AOAC method) Pancreatin, amyloglucosidase Chewing, α-amylase, amyloglucosidase

Englyst et al. (1992) Muir and O'Dea (1992)

Englyst, Kingman, et al. (1996) Skrabanja et al. (1999)

As per Englyst et al.(1992)

Bravo (1999)

70% barley wholemeal and 30% white wheat flour Wheat based products Wheat flour (Chapati, Poori and Phulka) Wheat flour and water at 2.5:1; salt and ground nut oil Cornflakes

Rice

Barley

Green banana

Green pea (65-Am) Pea

0.085% 0.67–1.0% 3% 6.5%

Whole grain

11.8%

Retrograded native rice starch Gelatinized rice starch Extruded flour (100 °C, 20% moisture) Raw, pure starch Autoclaved, high-amylose starch Dried flour at 52–58 °C

9.3% 8.6% 0.05% 4.1% 7.1% 41–59%

Biscuit (1:1 banana and wheat flour) Boiled seeds Autoclaved seeds Boiled and frozen Canned (autoclaved)

15% 33.4% 32.6% 6.3% 4.9%

seed of 23-Am (7.6% RS on a starch basis) had a lower level of RS than did boiled seed (12.85% RS on a starch basis), whereas autoclaved (32.6% RS) and boiled (33.4% RS) seed of 65-Am had similar levels of RS (Skrabanja, Liljeberg, Hedley, Kreft, & Björck, 1999). Three genetically-modified potato lines with different amylose contents were compared for their RS contents after similar gelatinization and retrogradation treatments (Leeman, Karlsson, Eliasson, & Björck, 2006). RS contents increased with increasing amylose content. For example, line 527-1 contained 1% amylose and 0.1% RS, Prevalent, 23% amylose and 5.3% RS, and line 342, 64% amylose and 26% RS. According to Åkerberg, Liljeberg, and Björck (1998), bread made from barley rich in amylopectin but low in amylose (3%) contained a lower amount of RS (∼ 2.5%) than did bread made from high (44%) amylose barley which contained ∼10% RS. The effect of amylose/amylopectin chain length on the levels of RS formed is a complex phenomenon. Comparing wild-type rice with mutants rich in RS, Shu et al. (2007) concluded that the level of RS in cooked rice could not be explained on the basis of amylose content alone. Instead, RS content was determined by the degree of polymerization (DP) of the side chains of amylopectin. Rice with high levels of RS had increased amounts of short chains (DP ≤ 12), and decreased amounts of intermediate (13 ≤ DP ≤ 36) and long (DP ≥ 37) chains. Cooked waxy maize starch with higher amounts of amylopectin long chains (DP N 13) than short chains (DP b 13) produced increasing amounts of RS over the cooling phase at 4 °C, and after 160 h the RS level reached approximately 45 g/ 100 g starch (Zhang, Sofyan, & Hamaker, 2008). Waxy maize starch with higher amounts of amylopectin short chains (DP b 13) than long chains (DP N 13) produced very low levels of RS (b5 g/100 g starch) during the cooling phase. Ao, Simsek, Zhang, Venkatachalam, Reuhs and Hamaker (2007) reported that partial hydrolysis of α-1,4 linkages of side chains of pre-gelatinized maize starch using β-amylase and maltogenic α-amylase and re-forming α-1,6 linkages using transglucosidase resulted in products that were higher in RS compared to untreated maize starch. Cairns, Morris, Botham, and Ring (1996) studied the degree of polymerization (DP) of retrograded pea starch gels and reported three levels (on a number average basis), with DP 107–108 and 26–28 being the most common types, and 5, a minor type, indicating the contribution of long chains to gel formation. Using

Englyst et al. (1992) Åkerberg, Liljeberg, Granfeldt, et al. (1998) Tharanathan and Tharanathan (2001)

Muir and O'Dea (1992) Chung et al. (2006) Chung et al. (2006) Faraj et al. (2004) Szczodrak and Pomeranz (1991) Szczodrak, and Pomeranz (1992) Tribess et al. (2009)

potato starch, Eerlingen, Deceuninck, and Delcour (1993) demonstrated that the DP of amylose (chain lengths from 40 to 610) was not related to the DP of RS (19–26) formed. Escarpa, González, Maňas, García-Diz, and Saura-Calixto (1996) adjusted amylose to amylopectin (extracted from potato starch) ratios to observe changes in RS contents. In an autoclave (115 °C, 2 bar, 20 min), samples of amylose, amylopectin and their mixtures were gelatinized with water at a ratio of 1:20. An amylose to amylopectin ratio of 100:0 produced 36.5% RS, and when the ratio was decreased to 50:50, the RS content decreased to 21.5%. When the ratio was changed to 0:100 (amylose: amylopectin), RS decreased further to 7.5%. These data clearly show that the RS contents of pulse and cereal starches, and of their starch pastes, vary with the genetic factors that influence amylose and amylopectin content and their chain lengths. Therefore, comparison of analytical protocols for determination of RS should consider the genetic origin of analytes, as comparison of RS values of food products having similar starch ingredients but with different genetic make-ups may lead to invalid conclusions. 7. Effect of processing on RS levels Available moisture and temperature influence starch gelatinization and retrogradation (Evans & Haisman, 1982; Liu & Thompson, 1998; Eerlingen, Crombez, et al., 1993; Eerlingen, Deceuninck, et al., 1993). Retrogradation of amylopectin occurs well at 2 °C forming elastic gels which melt above 100 °C (Ring, 1985). Amylose gels retrograde better at higher temperatures (Eerlingen, Crombez, & Delcour, 1993). Storage of gelatinized, amylose-rich wheat starch at a low temperature (0 °C) favours nucleation of the gel network; however, propagation of the network is weak due to the low mobility of molecules. The reverse is true during high temperature (100 °C) storage, where nucleation of the gel network is weak but propagation is favoured due to the increased mobility of molecules. During cooling an ‘ordered structure’ develops as double-helical regions of several amylose chains align parallel to each other, or single amylose chains fold to produce parallel areas, where folded regions are amorphous and the lamellae are crystalline. For example, the gel strength of potato starch is related to the storage temperature. Considering storage temperatures between 5 and 50 °C,

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Table 2 Resistant starch concentrations in pulses as influenced by genetics, processing method and RS analytical protocol. Starch source

Treatment

RS

Method of RS analysis

Author

Pea

Raw, flour

13.3% 14.7% 10.1% 12.6% 8.1% 9.7% 10% 10.9% 13.3%

AACC method 32–40 (2000) with modifications

Chung, Liu, Hoover, et al. (2008)

AACC method 32–40 (2000)

Chung, Liu, Donner, et al. (2008)

Englyst et al. (1992) with modifications

Chung, Liu, and Hoover (2009)

AACC method 32–40 (2000)

Chung, Liu, Pauls, et al. (2008)

AACC method 32–40 (2000) with modifications

Chung, Liu, Hoover, et al. (2008)

AACC method 32–40 (2000)

Chung, Liu, Donner, et al. (2008)

Englyst et al. (1992) with modifications

Chung, Liu, and Hoover (2009)

Englyst et al. (1992) with modification

Chung et al. (2010)

AACC method 32–40 (2000) with modifications

Chung, Liu, Hoover, et al. (2008)

AACC method 32–40 (2000)

Chung, Liu, Donner, et al. (2008)

Goñi et al. (1996)

Bravo et al. (1998)

Goñi et al. (1996)

Bravo et al. (1998)

Goñi et al. (1996)

Bravo et al. (1998)

Englyst et al. (1992) with modification

Chung et al. (2010)

Pea

Pea

Common bean

Lentils Lentils Lentils

Lentil starch-gelatinized

Chickpea

Chickpea

Moth bean

Horse gram

Black gram

Navy bean starch-gelatinized Cultivar AC Compass

Cultivar — 1674–13 Cultivar — 1215–33 Cultivar — 1329–12 Starch Cultivar — 1674–13 Cultivar — 1215–33 Cultivar — 1329–12 Raw Cultivar — 1674–13 Annealed (15 °C; 70% moisture; 24 h) Heat-moisture treatment (100 °C; 30% moisture; 2 h) Heat-moisture treatment (120 °C; 30% moisture; 2 h) Raw flour Cultivar — Majesty Cultivar — Red Kanner Cultivar — AC Nautica Starch Cultivar — Majesty Cultivar — Red Kanner Cultivar — AC Nautica Raw flour Cultivar — CDC Meteor Cultivar — CDC Robin Starch Cultivar — CDC Meteor Cultivar — CDC Robin Raw Cultivar — CDC Meteor Annealed (15 °C; 70% moisture; 24 h) Heat-moisture treatment (100 °C; 30% moisture; 2 h) Heat-moisture treatment (120 °C; 30% moisture; 2 h) Native Cultivar 1544-8 Annealed with 70% moisture for 24 h at 50 °C Heat-moisture treatment (30% moisture + 24 h at ambient temperature + 120 °C for 24 h) Annealed and then heat-moisture treated Heat-moisture treated and then annealed Raw flour Cultivar — Myles Cultivar — FLIP 97-101C Cultivar — 97-Indian2-11 Starch Cultivar — Myles Cultivar — FLIP 97-101C Cultivar — 97-Indian2-11 Raw Freshly cooked Cooked; stored at 4 °C for 24 h Raw Freshly cooked Cooked; stored at 4 °C for 24 h Raw Freshly cooked Cooked; stored at 4 °C for 24 h Native Annealed with 70% moisture for 24 h at 50 °C Heat-moisture treatment (30% moisture + 24 h at ambient temperature + 120 °C for 24 h) Annealed and then heat-moisture treated Heat-moisture treated and then annealed

14.5% 36% 35.5% 32.4% 21.3% 21.9% 17.2% 14.9% 14.4% 13% 13.2% 9.1% 11.4% 13.2% 14.7% 12.8% 14.1% 17.5%

18.5% 19.6% 6.4% 4.7% 3.1% 8.4% 18.4% 13.3% 12.2% 3.9% 4.8% 26.4% 5.2% 5.8% 19.7% 3.4% 4% 14.8% 16.4% 19.8%

20.5% 21.9%

the higher the storage temperature, the higher the gel strength, provided the starch content is N50% (Nakazawa, Noguchi, Takahashi, & Takada, 1985). X-ray diffraction studies showed that two different types of crystals were formed during retrogradation of wheat starch at 40 and 95 °C. At higher temperatures, wheat starch retrograded to form structures with a large number of lamellae and having large particle sizes. Resistance to α-amylase increased as the number of lamellae in crystals increased (Zabar, Shimoni, & Bianco-Peled, 2008). Lamellae do not form along the entire length of the amylose chain, rather about 24

glucose molecules of an amylose chain participate in lamella formation (Eerlingen, Crombez, et al., 1993; Eerlingen, Deceuninck, et al., 1993). These helices are thought to be formed through hydrogen bonding (Wu & Sarko, 1978). As retrogradation proceeds, double helices are organized into ‘hexagonal cells’ (Haralampu, 2000). Through their influence on gelatinization and retrogradation, differences in the conditions of food processing, such as changes in moisture, temperature and duration of heating and subsequent cooling, influence the RS content of foods.

A. Perera et al. / Food Research International 43 (2010) 1959–1974

Recent publications describing the influence of processing method on variations in the RS contents of pulses and pulse products are summarized in Table 2. For three cultivars of pea, 1674-13, 1215-33 and 1329-12, refined starch contained less RS than did the meal (Chung, Liu, Hoover, et al., 2008), presumably due to the elimination of structural impediments to amylase hydrolysis, i.e. a reduction in RS1 levels, during starch extraction. This observation also was applicable to starch isolated from the common bean cultivars Majesty, Red Kanner and AC Nautica (Chung, Liu, Pauls, et al., 2008). For the chickpea cultivars Myles, FLIP 97101C and 97-Indian 2-11, starch contained more RS (Chung, Liu, Donner, et al., 2008) than did the meal (Chung, Liu, Hoover, et al., 2008). In these studies, pulse flours were prepared with a cyclone mill and starch was isolated by the same procedure in each case. However, the analytical procedures used to determine RS in chickpea starch and meal differed slightly, making it difficult to draw conclusions from the observations. Raw moth bean, horse gram and black gram had considerably higher RS values than did cooked beans. When the cooked pulses were stored at 4 °C for 24 h, RS contents increased slightly (Bravo, Siddhuraju, & SauraCalixto, 1998). The cotyledons of some pulses, e.g. bean (Phaseolus vulgaris L.), contain mammalian and insect α-amylase inhibitors as part of the seeds' defence mechanism (Moreno, Altabella, and Chrispeels,

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1990), the presence of which may result in very high levels of resistant starch in assays of raw flours and meals. The effect of processing on the RS content of some cereal products is presented in Table 3. Han and Lim (2009) reported significantly higher RS values for japonica brown rice as the moisture content of soaked rice reached 20%, compared to rice containing 30% moisture prior to cooking. As reported by Chung et al. (2006), native waxy rice starch had the highest level of RS (∼9%), whereas gelatinized waxy rice starch (∼3%) and retrograded, gelatinized waxy rice starch (3–3.8%) had the lowest levels of RS. The observation of higher RS levels in native waxy starch than in gelatinized and retrograded waxy starches is expected, as all or some of the RS1 and RS2 in native waxy starch may be converted to enzyme hydrolysable starch during heating, and the formation of RS in the high-amylopectin waxy starches would not be extensive (Eerlingen & Delcour, 1995; Russel, Berry, & Greenwell, 1989). This idea is supported by the observation that waxy rice starch, partially gelatinized at 60 or 70 °C, had RS contents (8.6 and 7.7%, respectively) similar to that of native waxy starch. The RS contents of retrograded gels of wheat, corn and potato were increased significantly when starch was used instead of flour (as expected), but the opposite was reported for rice (GarcíaAlonso, Jiménez-Escrig, Martín-Carrón, Bravo, & Saura-Calixto, 1999).

Table 3 Resistant starch concentrations in cereal starches as influenced by processing. Starch source

Treatment

Japonica brown rice Pre-soaked in water at 25 or 50 °C to reach 20% moisture + cooked Pre-soaked in water at 25 or 50 °C to reach 30% moisture + cooked Waxy rice Native waxy rice starch Gelatinized starch Partially gelatinized starch at 60 °C for 5 min Partially gelatinized starch at 70 °C for 5 min Pastry wheat flour Extruded at 20% moisture; 150/200/250 rpm; 40–120 °C; stored at 4 °C/0 days Extruded at 20% moisture; 150/200/250 rpm; 40–120 °C; stored at 4 °C/7–14 days Extruded at 40% moisture; 150/200/250 rpm; 40–120 °C; stored at 4 °C/0 days Extruded at 40% moisture; 150/200/250 rpm; 40–120 °C; stored at 4 °C/7–14 days Extruded at 60% moisture; 150/200/250 rpm; 40–120 °C; stored at 4 °C/0 days Extruded at 60% moisture; 150/200/250 rpm; 40–120 °C; stored at 4 °C/7–14 days Corn Acid modified with 1.64 M HCl at 40 °C for 4 h + gelatinized + autoclaved + lyophilized

RS

Method of RS analysis

Author

29.2–32.4% 20.7–25.9% 9.3% 3.0% 8.6% 7.7% 0.48–0.52% 1.21–1.35% 0.63–0.67% 1.52–1.86% 2.54–2.65% 3.55–4.25% 5%

Englyst et al. (1992)

Han, and Lim (2009)

Englyst et al. (1992)

Chung et al. (2006)

Megazyme® assay

Kim et al. (2006)

AOAC 991.43 (1998)

Koksel, Masatcioglu, Kahraman, Ozturk, and Basman (2008)

12%

Corn

Acid modified with 1.64 M HCl at 40 °C for 4 h + gelatinized + autoclaved + Stored at 95 °C for 48 h + lyophilized Normal corn starch

18.3% 16.9%

Corn

Annealed with excess water for 24 h at 50 °C Heat-moisture treatment (30% moisture + 24 h at ambient temperature + 120 °C for 24 h) Annealed with excess water for 24 h at 50 °C + Heat-moisture treatment (30% moisture + 24 h ambient temperature + 120 °C for 24 h) Heat-moisture treatment (30% moisture + 24 h ambient temperature + 120 °C for 24 h) + annealed with excess water for 24 h at 50 °C Native corn starch Heat-moisture treatment — 30% moisture + 100 °C for 60 min 30% moisture + 120 °C for 60 min Native wheat starch Heat-moisture treatment — 30% moisture + 80 °C for 60 min 30% moisture + 100 °C for 60 min Autoclaved at 120 °C + Stored at 4 °C for 24 h (repeated twice) Autoclaved at 120 °C + Stored at 4 °C for 24 h (repeated twice) + hydrolysed with 0.1 M citric acid Treated with acid (HCl) and methanol at 25 °C for 30 days Treated with acid (HCl) and methanol treatment at 25 °C for 30 days + annealed at 50 °C for 72 h with water 0 kGy Gamma irradiation (60Co) 10 kGy (2 kGy/h) 10 kGy (0.67 kGy/h) 10 kGy (0.40 kGy/h)

1.5%

Wheat

High-amylose corn

Corn (normal)

Corn (normal)

19.7%

Englyst et al. (1992) modified as Chung, Hoover, and Liu per Chung, Liu, et al. (2009) (2009)

17.3% 19.7%

1.3%

AOAC 991.43 (1985)

Brumovsky, Brumovsky, Fretes, and Peralta (2009)

Goñi et al. (1996)

Zhao and Lin (2009)

∼12% ∼38%

Englyst et al. (1992)

Lin et al. (2009)

19.7% 22.2% 23.0% 24.7%

Englyst et al. (1992)

Chung and Liu (2009b)

4.2% 1.0% 1.9% 1.6% 30% 39%

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Green banana starch is a rich source of RS but the amounts varied significantly (41–59%) with the method of drying employed during starch processing (Tribess et al., 2009). Heat-moisture treatments (30% moisture, 24 h at ambient temperature, heated at 100 or 120 °C for 2 h) were applied to corn (Table 3) and lentil and pea (Table 2) starches, with and without a pre-gelatinization treatment (Chung, Liu, & Hoover, 2009). The heat-moisture treatment increased RS levels considerably. For example, native corn, lentil and pea starches had RS contents of 5, 9 and 10% respectively; corresponding values were increased to 12%, 15% and 15% after the 120 °C heatmoisture treatment. In another experiment, a heat-moisture treatment (30% moisture, 24 h at ambient temperature, heated at 120 °C for 24 h) decreased the level of RS in corn starch (16.9%) compared to that of native, normal corn starch (19.7%). A subsequent annealing treatment (sample to water ratio of 3:7, 50 °C, 24 h) compensated for the lower RS content (Chung, Hoover, & Liu, 2009). Heating of corn starch at 30% moisture for 40 or 60 min at 100 °C or 120 °C yielded products with 1.3 and 1.5% RS, respectively, at 100 °C and with 1.8 and 4.2% RS, respectively, at 120 °C, illustrating the significance of the combined time and temperature effect on RS levels (Brumovsky, Brumovsky, Fretes, & Peralta, 2009). Annealed and/or heat-moisture-treated pulse starches which were subsequently gelatinized produced higher amounts of RS than did gelatinization of native starches (Chung, Liu, & Hoover, 2010). For example, gelatinized, native lentil and navy bean starches contained 12.8 and 14.8 g RS/100 g starch, respectively. Lentil starch annealed (70% moisture, 24 h, 50 °C) and subsequently heatmoisture treated (30% moisture, 120 °C, 24 h), and heat-moisturetreated lentil starch which was subsequently annealed, exhibited RS levels of 18.5 and 19.6 g/100 g starch, respectively, after gelatinization (Table 2). Corresponding values for navy bean after gelatinization were 20.5 and 21.9 g/100 g starch (Table 2). The effect of extrusion pelletizing on RS was determined with barley, wheat, oat, corn and rice. Dough was cooked at 95 °C for 1 h before extrusion and then dried at 100 °C for 1 h. For all grain types used, with the exception of rice, a significant reduction in RS was reported after extrusion (Hernot, Boileau, Bauer, Swanson, & Fahey, 2008). The RS level of extruded pastry wheat flour increased as the initial moisture level of the feed (20, 40 or 60%) and post-process storage time at 4 °C (0, 7 or 14 days) increased (Kim, Tanhehco, & Ng, 2006) (Table 3). High-amylose corn starches (Hylon VII and Gelose 80; 70 and 80% amylose and 60 and 46% RS, respectively) subjected to extrusion cooking (35 and 50% moisture, 100 and 140 °C, 150 and 750 s−1 shear) exhibited significantly reduced RS concentrations (14 and 17%, respectively). This was thought to be due to enhanced opportunities for amylase action after shear damage to starch granules (Htoon et al., 2009). Both a pre-gelatinization treatment of corn starch with HCl at 40 °C (Koksel et al., 2008) and a post-retrogradation treatment of high-amylose corn starch with citric acid (Zhao & Lin, 2009) increased the level of RS (Table 3). Wheat and corn starch cooked at 100 °C for 10 min during an in vitro digestibility assay had RS levels of 9 and 11.4%, respectively; similar levels of RS were seen in wheat (10.9%) and corn (13.3%) starch autoclaved three times at 121 °C for 15 min and then cooled within 15 min (Hickman, Janaswamy, & Yao, 2009). Starch autoclaved as above, and subsequently dried, when subjected to β-amylase hydrolysis at pH 5.5 and 55 °C for 20 h exhibited significantly higher levels of RS, 23.1 and 29.9% in wheat and corn starch, respectively (Hickman et al., 2009). Commercially available canned beans had lower levels of RS than did canned bean flour prepared after drying at 50 °C (Osorio-Díaz et al., 2002). RS levels in corn starch subjected to acid–methanol treatment only or acid–methanol treatment combined with annealing at 50 °C for 72 h were 12 and 38 g/100 g starch, respectively (Lin, Wang, & Chang, 2009). Gamma irradiation at 10 or 50 kGy (dose rate of 2 kGy/h at room temperature) increased the RS content of corn starch from 19.7% to 2.2 and 25.1%, respectively (Chung and Liu, 2009b). It is apparent that even minor differences in the conditions under which starch gelatinization and retrogradation are achieved can lead

to significant differences in the RS contents of foods and food ingredients. Therefore, meaningful comparison of analytical procedures for RS determination requires analysis of foods processed under identical conditions. Comparison of analytical procedures for RS using currently available data is difficult as the analytes used are often dissimilar. 8. Conclusion Analytical procedures for RS vary with respect to the sample preparation method, particle size of samples, nature of the preliminary heat treatments for raw analytes (if any), enzymes and buffers employed, incubation temperatures, sampling of the enzyme digests, chemicals and conditions of hydrolysis, and the glucose determination method. The effects of these changes on the RS values obtained generally cannot be compared as the analytes used were not identical in most cases. Genetic differences with respect to the source of starch, type of processing (meal vs. starch) and conditions of processing (partial vs. complete gelatinization), chemical modification of samples, and storage conditions significantly influence RS values. Therefore, the concept of RS in a food material is a subjective parameter and any generalizations made for a particular food item or category must be made with caution. References AACC International (2000). Approved methods of the American association of cereal chemists. St. Paul, MN: AACC, Inc. Abdulnour-Nakhoul, S., Nakhoul, N. L., Wheeler, S. A., Wang, P., Swenson, E. R., & Orlando, R. C. (2005). HCO3− secretion in the esophagal submucosal glands. American Journal of Physiology, 22, G736−G744. Åkerberg, A., Liljeberg, H., & Björck, I. (1998). Effects of amylose/amylopectin ratio and baking conditions on resistant starch formation and glycaemic indices. Journal of Cereal Science, 28, 71−80. Åkerberg, A. K. E., Liljeberg, H. G. M., Granfeldt, Y. E., Drews, A. W., & Björck, I. M. E. (1998). An in vitro method, based on chewing, to predict resistant starch content in foods allows parallel determination of potentially available starch and dietary fiber. The Journal of Nutrition, 12, 651−660. Ao, Z., Simsek, S., Zhang, G., Venkatachalam, M., Reuhs, B. L., & Hamaker, B. R. (2007). Starch with a slow digestion property produced by altering its chain length, branch density, and crystalline structure. Journal of Agricultural and Food Chemistry, 55, 4540−4547. AOAC (1985). Official methods of analysis. Arlington, VA: AOAC. AOAC (1998). Official methods of analysis. Arlington, VA: AOAC. Bailey, J. M., & Whelan, W. J. (1961). Physical properties of starch I. Relationship between iodine stain and chain length. Journal of Biological Chemistry, 236(4), 969−973. Bertoft, E. (2004). Understanding starch structure and functionality. In A. Eliasson (Ed.), Starch in food: Structure, function and applications (pp. 156−184)., 1st ed. Cambridge: Woodhead Publishing Limited. Bird, A. R., Brown, I. L., & Topping, D. L. (2000). Starches, resistant starches, the gut microflora and human health. Current Issues in Intestinal Microbiology, 1(1), 25−37. Bravo, L. (1999). Effect of processing on the non-starch polysaccharides and in vitro starch digestibility of legumes. Food Science and Technology International, 5, 415−423. Bravo, L., Siddhuraju, P., & Saura-Calixto, F. (1998). Effect of various processing methods on the in vitro starch digestibility and resistant starch content of Indian pulses. Journal of Agricultural and Food Chemistry, 46, 4667−4674. Brouns, F., Kettlitz, B., & Arrigoni, E. (2002). Resistant starch and butyrate revolution. Trends in Food Science & Technology, 13, 251−261. Brumovsky, L. A., Brumovsky, J. O., Fretes, M. R., & Peralta, J. M. (2009). Quantification of resistant starch in several starch sources treated thermally. International Journal of Food Properties, 12, 451−460. Cairns, P., Morris, V. J., Botham, R. L., & Ring, S. G. (1996). Physicochemical studies on resistant starch in vitro and in vivo. Journal of Cereal Science, 23, 265−275. Cairns, P., Sun, L., Morris, V. J., & Ring, S. G. (1995). Physicochemical studies using amylose as an in vitro model for resistant starch. Journal of Cereal Science, 21(1), 37−47. Chibbar, R. N., Ganeshan, S., & Båga, M. (2007). In planta novel starch synthesis. In P. Ranalli (Ed.), Improvement of crop plants for industrial end uses (pp. 181−208). The Netherlands: Springer. Chow, P. (2008). The rationale for the use of animal models in biomedical research. In P. K. H. Chow, R. T. H. Ng, & B. E. Ogden (Eds.), Using animal models in biomedical research (pp. 2−10). Singapore: World Scientific Publishing Company Pte Limited Available from: bhttp://www.worldscibooks.com/etextbook/6454/6454_chap01. pdfN. Accessed October 08, 2009. Chung, H., Hoover, R., & Liu, Q. (2009). The impact of single and dual hydrothermal modifications on the molecular structure and physicochemical properties of normal corn starch. International Journal of Biological Macromolecules, 44, 203−210. Chung, H., Lim, H., & Lim, S. (2006). Effect of partial gelatinization and retrogradation on the enzymic digestion of waxy rice starch. Journal of Cereal Science, 43, 353−359.

A. Perera et al. / Food Research International 43 (2010) 1959–1974 Chung, H., & Liu, Q. (2009a). Impact of molecular structure of amylopectin and amylose on amylose chain association during cooling. Carbohydrate Polymers, 77, 807−815. Chung, H. J., & Liu, Q. (2009b). Effect of gamma irradiation on molecular structure and physicochemical properties of corn starch. Journal of Food Science, 74(5), 353−361. Chung, H., Liu, Q., Donner, E., Hoover, R., Warkentin, T. D., & Vandenberg, B. (2008). Composition, molecular structure, properties, and in vitro digestibility of starches from newly released Canadian pulse cultivars. Cereal Chemistry, 85(4), 471−479. Chung, H., Liu, Q., & Hoover, R. (2009). Impact of annealing and heat-moisture treatment on rapidly digestible, slowly digestible and resistant starch levels in native and gelatinized corn, pea and lentil starches. Carbohydrate Polymers, 75, 436−447. Chung, H., Liu, Q., & Hoover, R. (2010). Effect of single and dual hydrothermal treatments on the crystalline structure, thermal properties and nutritional fractions of pea, lentil and navy bean starches. Food Research International, 43(2), 501−508. Chung, H., Liu, Q., Hoover, R., Warkentin, T. D., & Vandenberg, B. (2008). In vitro starch digestibility, expected glycemic index, and thermal and pasting properties of flours from pea, lentil and chickpea cultivars. Food Chemistry, 111, 316−321. Chung, H., Liu, Q., Pauls, P., Fan, M. Z., & Yada, R. (2008). In vitro starch digestibility, expected glycemic index and some physicochemical properties of starch and flour from common bean (Phaseolus vulgaris L.) varieties grown in Canada. Food Research International, 41, 869−875. Cichoke, A. J. (1998). The complete book of enzyme therapy.New York: Penguin Putnam Inc. 10–16 pp. Correa, P. (1988). A human model of gastric carcinogenesis 1. Cancer Research, 48, 3554−3560. Correa, F., Angelina, T., Reis, P. M., Maria, S., & de Oliveira Costa, A. (2009). Increase in digestive organs of rats due to the ingestion of dietary fibre with similar solubility to that of common bean. Archivos Latinoamericanos De Nutricon, 59(1), 47−53. Cummings, J. H., Beatty, E. R., Kingman, S. M., Bingham, S. A., & Englyst, H. N. (1996). Digestion and physiological properties of resistant starch in the human large bowel. British Journal of Nutrition, 75, 733−747. DeSesso, J. M., & Jacobson, C. F. (2001). Anatomical physiological parameters affecting gastrointestinal absorption in humans and rats. Food and Chemical Toxicology, 39, 209−228. Donald, A. M. (2004). Understanding starch structure and functionality. In A. Eliasson (Ed.), Starch in food: Structure, function and applications (pp. 156−184). Cambridge: Woodhead Publishing Limited. Dronamraju, S. S., Coxhead, J. M., Kelly, S. B., & Mathers, J. C. (2007). Role of resistant starch in colorectal cancer prevention: A prospective randomised controlled trial. American Journal of Gastroenterology, 102(S2), 556−557. Eerlingen, R. C., Crombez, M., & Delcour, J. A. (1993). Enzyme-resistant starch. I. Quantitative and qualitative influence of incubation time and temperature of autoclaved starch on resistant starch formation. Cereal Chemistry, 70(3), 339−344. Eerlingen, R. C., Deceuninck, M., & Delcour, J. A. (1993). Enzyme resistant starch II. Influence of amylose chain length on resistant starch formation. Cereal Chemistry, 70(3), 345−350. Eerlingen, R. C., & Delcour, J. A. (1995). Formation, analysis and properties of type III enzyme resistant starch. Journal of Cereal Science, 22, 129−138. Englyst, H. N., & Cummings, J. H. (1985). Digestion of the polysaccharides of some cereal foods in the human small intestine. American Journal of Clinical Nutrition, 42, 778−787. Englyst, H. N., & Cummings, J. H. (1986). Digestion of the carbohydrates in banana (Musa paradisiaca sapientum) in the human small intestine. The American Journal of Clinical Nutrition, 44, 42−50. Englyst, H. N., & Cummings, J. H. (1987a). Digestion of the polysaccharides of potato in the small intestine of man. American Journal of Clinical Nutrition, 45, 423−431. Englyst, H. N., & Cummings, J. H. (1987b). Resistant starch, a ‘new’ food component: A classification of starch for nutritional purposes. In I. D. Morton (Ed.), Cereals in a European context (pp. 221−233). New York: First European Conference on Food Science and Technology. Englyst, H. N., & Hudson, G. L. (1996). The classification and measurement of dietary carbohydrates. Food Chemistry, 57(1), 15−21. Englyst, H. N., Kingman, S. M., & Cummings, J. H. (1992). Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition, 46, S33−S50. Englyst, H. N., Kingman, S. M., Hudson, G. J., & Cummings, J. H. (1996). Measurement of resistant starch in vitro and in vivo. British Journal of Nutrition, 75, 749−755. Englyst, H. N., Veenstra, J., & Hudson, G. L. (1996). Measurement of rapidly available glucose (RAG) in plant foods: A potential in vitro predictor of the glycaemic response. British Journal of Nutrition, 75, 327−337. Englyst, H. N., Wiggins, H. S., & Cummings, J. H. (1982). Determination of the non-starch polysaccharides in plant foods by gas liquid chromatography of constituent sugars as alditol acetates. Analyst, 107, 307−318. Escarpa, A., González, M. C., Maňas, E., García-Diz, L., & Saura-Calixto, F. (1996). Resistant starch formation: Standardization of a high-pressure autoclave process. Journal of Agricultural and Food Chemistry, 44, 924−928. Evans, D., & Haisman, D. R. (1982). The effect of solutes on the gelatinization temperature range of potato starch. Starch, 34(7), 224−231. Faraj, A., Vasanthan, T., & Hoover, R. (2004). The effect of extrusion cooking on resistant starch formation in waxy and regular barley flours. Food Research International, 37, 517−525. García-Alonso, A., Jiménez-Escrig, A., Martín-Carrón, N., Bravo, L., & Saura-Calixto, F. (1999). Assessment of some parameters involved in the gelatinization and retrogradation of starch. Food Chemistry, 66, 181−187. German, M. L., Blumenfeld, A. L., Guenin, Y. V., Yuryev, V. P., & Toistoguz, V. B. (1992). Structure formation in systems containing amylose, amylopectin and their mixtures. Carbohydrate Polymers, 18, 27−34.

1973

Goñi, I., García-Diza, L., Mańasb, E., & Saura-Calixto, F. (1996). Analysis of resistant starch: A method for foods and food product. Food Chemistry, 56(4), 445−459. Grabitske, H. A., & Slavin, J. L. (2009). Gastrointestinal effects of low-digestible carbohydrates. Critical Reviews in Food Science and Nutrition, 49, 327−360. Granito, M., Michel, C., Frías, J., Champ, M., & Guerra, M. (2005). Fermented Phaseolus vulgaris: Acceptability and intestinal effects. European Food Research and Technology, 220, 182−186. Hamer, H. M., Jonkers, D. M. A. E., Bast, A., Vanhoutvin, S. A. L. W., Fischer, M. A. G., Kodde, A., et al. (2009). Butyrate modulates oxidative stress in the colonic mucosa of healthy humans. Clinical Nutrition, 28, 88−93. Han, J., & Lim, S. (2009). Effect of presoaking on textural, thermal, and digestive properties of cooked brown rice. Cereal Chemistry, 86(1), 100−105. Haralampu, S. G. (2000). Resistant starch — A review of the physical properties and biological impact of RS3. Carbohydrate Polymers, 41, 285−292. Hernot, D. C., Boileau, T. W., Bauer, L. L., Swanson, K. S., & Fahey, G. C. (2008). In vitro digestion characteristics of unprocessed and processed whole grains and their components. Journal of Agricultural and Food Chemistry, 56, 10,721−10,726. Hickman, E., Janaswamy, S., & Yao, Y. (2009). Autoclave and β-amylosis lead to reduced in vitro digestability of starch. Journal of Agricultural and Food Chemistry, 57, 7005−7012. Htoon, A., Shrestha, A. K., Flanagan, B. M., Lopez-Rubio, A., Bird, A. R., Gilbert, E. P., et al. (2009). Effects of processing high amylose maize starches under controlled conditions on structural organisation and amylase digestibility. Carbohydrate Polymers, 75, 236−245. Hylla, S., Gostner, A., Dusel, G., Anger, H., Bartram, H., Christl, S. U., et al. (1998). Effects of resistant starch on the colon in healthy volunteers: Possible implications for cancer prevention. American Journal of Clinical Nutrition, 6, 136−142. Kendall, C. W. C., Esfahani, A., Hoffman, A. J., Evans, A., Sanders, L. M., Josse, A. R., et al. (2008). Effect of novel maize-based dietary fibers on postprandial glycemia and insulinemia. Journal of the American College of Nutrition, 27(6), 711−718. Kim, J. H., Tanhehco, E. J., & Ng, P. K. W. (2006). Effect of extrusion conditions on resistant starch formation from pastry wheat flour. Food Chemistry, 99, 718−723. Koksel, H., Masatcioglu, T., Kahraman, K., Ozturk, S., & Basman, A. (2008). Improving effect of lyophilization on functional properties of resistant starch preparations formed by acid hydrolysis and heat treatment. Journal of Cereal Science, 47, 275−282. Leeman, A. M., Karlsson, M. E., Eliasson, A., & Björck, I. M. E. (2006). Resistant starch formation in temperature treated potato starches varying in amylose/amylopectin ratio. Carbohydrate Polymers, 6, 306−313. Leu, R. K. L., Hu, Y., Brown, I. L., & Young, G. P. (2009). Effect of high amylose maize starches on colonic fermentation and apoptotic response to DNA-damage in the colon of rats. Nutrition & Metabolism, 6(1), 11−20. Lin, J., Wang, S., & Chang, Y. (2009). Impacts of acid–methanol treatment and annealing on the enzymatic resistance of corn starches. Food Hydrocolloids, 23, 1465−1472. Liu, Q., & Thompson, D. B. (1998). Effects of moisture content and different gelatinization heating temperatures on retrogradation of waxy-type maize starches. Carbohydrate Research, 314, 221−235. Maki, K. C., Sanders, L. M., Reeves, M. S., Kaden, V. N., Rains, T. M., & Cartwright, Y. (2009). Beneficial effects of resistant starch on laxation in healthy adults. International Journal of Food Science and Nutrition, 60(S4), 296−305. Makinen, K. K. (1989). Salivary enzymes. In J. O. Tenovuo (Ed.), Human saliva: Clinical chemistry and microbiology (volume II) (pp. 94−114). Florida: CRC Press. Megazyme (2008). Resistant starch assay procedure.http://secure.megazyme.com/ downloads/en/data/K-RSTAR.pdf Accessed July 25, 2009. Moreno, J., Altabella, T., & Chrispeels, M. J. (1990). Characterization of α-amylase inhibitor, a lectin-like protein in the seeds of Phaseolus vulgaris. Plant Physiology, 92, 703−709. Muir, J. G., & O'Dea, K. (1992). Measurement of resistant starch: Factors affecting the amount of starch escaping digestion in vitro. Journal of Clinical Nutrition, 56, 123−127. Nakazawa, F., Noguchi, S., Takahashi, J., & Takada, M. (1985). Retrogradation of gelatinized potato starch studied by differential scanning calorimetry. Agricultural and Biological Chemistry, 49(4), 953−957. Nordgaard, I., & Mortensen, P. B. (1995). Digestive process in the human colon. Nutrition, 11(1), 37−45. Osorio-Díaz, P., Bello-Pérez, L. A., Agama-Acevedo, E., Vargas-Torres, A., Tovar, J., & ParedesLópez, O. (2002). In vitro digestibility and resistant starch content of some industrialized commercial beans (Phaseolus vulgaris L.). Food Chemistry, 78, 333−337. Rabbani, G. H., Ahmed, S., Hossain, I., Islam, R., Marni, F., Akhtar, M., et al. (2009). Green banana reduces clinical severity of childhood shigellosis: A double-blind, randomized, controlled clinical trial. The Pediatric Infectious Disease Journal, 28(5), 420−425. Rahman, S., Birda, A., Reginaa, A., Lia, Z., Rala, J. P., McMaugha, S., et al. (2007). Resistant starch in cereals: Exploiting genetic engineering and genetic variation. Journal of Cereal Science, 46, 251−260. Reddy, B. S., Ernst, L., & Wynderm, D. (1977). Metabolic epidemiology of colon cancer: Fecal bile acids and neutral sterols in colon cancer patients and patients with adenomatous polyps. Cancer, 39, 2533−2539. Ring, S. G. (1985). Observations on the crystallization of amylopectin from aqueous solution. International Journal of Biological Macromolecules, 7(4), 253−254. Rundle, R. E. (1947). The configuration of starch in the starch–iodine complex. V. Fourier projections from X-ray diagrams. Journal of American Chemical Society, 69 (7), 1769−1772. Russel, C. L., Berry, P. S., & Greenwell, P. (1989). Characterization of resistant starch from wheat and maize. Journal of Cereal Science, 9(1), 1−15. Sajilatha, M. G., Singhal, R. S., & Kulkarni, P. R. (2006). Resistant starch: A review. Comprehensive Reviews in Food Science and Food Safety, 5, 1−17. Sang, Y., Bean, S., Seib, P. A., Pedersen, J., & Shi, Y. (2008). Structure and functional properties of sorghum starches differing in amylose content. Journal of Agricultural and Food Chemistry, 56, 6680−6685.

1974

A. Perera et al. / Food Research International 43 (2010) 1959–1974

Saura-Calixto, F., Goňi, I., Bravo, L. E., & Maňas, E. (1993). Resistant starch in foods: Modified method for dietary fiber residues. Journal of Food Science, 58(3), 642−643. Seib, P. A., and Woo, K. (1999). Food grade starch resistant to α-amylase and the method of preparing the same. US Patent Number 5,855,946. Available from bhttp: //www.freepatentsonline.com/5855946.pdfN. Accessed 30 April, 2010. Shu, X., Jiaa, L., Gao, J., Song, Y., Zhao, H., Nakamura, Y., et al. (2007). The influences of chain length of amylopectin on resistant starch in rice (Oryza sativa L.). Starch, 59, 504−509. Silvi, S., Rumney, C. J., Cresci, A., & Rowland, I. R. (1999). Resistant starch modifies gut microflora and microbial metabolism in human flora-associated rats inoculated with faeces from Italian and UK donors. Journal of Applied Microbiology, 86, 521−530. Skrabanja, V., Liljeberg, H. G. M., Hedley, C. L., Kreft, I., & Björck, I. M. E. (1999). Influence of genotype and processing on the in vitro rate of starch hydrolysis and resistant starch formation in peas (Pisum sativum L.). Journal of Agricultural and Food Chemistry, 47, 2033−2039. Smith, A. M. (2001). The biosynthesis of starch granules. Biomacromolecules, 2, 335−341. Storey, D., Lee, A., Bornet, F., & Brouns, F. (2007). Gastrointestinal responses following acute and medium term intake of retrograded resistant maltodextrins, classified as type 3 resistant starch. European Journal of Clinical Nutrition, 61, 1262−1270. Szczodrak, J., & Pomeranz, Y. (1991). Starch and enzyme-resistant starch from highamylose barley. Cereal Chemistry, 68(6), 589−596. Szczodrak, J., & Pomeranz, Y. (1992). Starch–lipid interactions and formation of resistant starch in high amylose barley. Cereal Chemistry, 69(6), 626−632. Tharanathan, M., & Tharanathan, R. N. (2001). Resistant starch in wheat-based products: Isolation and characterization. Journal of Cereal Science, 34, 73−84. Tribess, T. B., Hernández-Uribe, J. P., Méndez-Montealvo, M. G. C., Menezes, E. W., BelloPerez, L. A., & Tadini, C. C. (2009). Thermal properties and resistant starch content of green banana flour (Musa cavendishii) produced at different drying conditions. Food Science & Technology, 42, 1022−1025. Umemoto, T., Yano, M., Satoh, H., Shomura, A., & Nakamura, Y. (2002). Mapping of a gene responsible for the difference in amylopectin structure between japonica-type and indica-type rice varieties. Theoretical and Applied Genetics, 104, 1−8.

van de Wal, M., D'Hulst, C., Vincken, J., Buléon, A., Visser, R., & Ball, S. (1998). Amylose is synthesized in vitro by extension of and cleavage from amylopectin. Journal of Biological Chemistry, 273(35), 22,232−22,240. Vrinten, P. L., & Nakamura, T. (2000). Wheat granule-bound starch synthase I and II are encoded by separate genes that are expressed in different tissues. Plant Physiology, 122, 255−263. Wang, Z., Zheng, F., Shen, G., Gao, J., Snusted, D. P., Li, M., et al. (1995). The amylose content in rice endosperm is related to the post-transcriptional regulation of the waxy gene. The Plant Journal, 7(4), 613−622. Wolf, B. W., Bauer, L. L., & Fahey, G. C. (1999). Effects of chemical modification on in vitro rate and extent of food starch digestion: An attempt to discover a slowly digested starch. Journal of Agricultural and Food Chemistry, 47, 4178−4183. Wong, J. M. W., de Souza, R., Kendall, C. W. C., Emam, A., & Jenkins, D. J. A. (2006). Colonic health: Fermentation and short chain fatty acids. Journal of Clinical Gastroenterology, 40(3), 235−243. Wu, H. C. H., & Sarko, A. (1978). The double-helical molecular structure of crystalline Bamylose. Carbohydrate Research, 61, 7−25. Xue, Q., Newman, R. K., & Newman, C. W. (1996). Effects of heat treatment of barley starches on in vitro digestibility and glucose responses in rats. Cereal Chemistry, 73 (5), 588−592. Yao, N., Paez, A. V., & White, P. J. (2009). Structure and function of starch and resistant starch from corn with different doses of mutant amylase-extender and floury-1 alleles. Journal of Agricultural and Food Chemistry, 57, 2040−2048. Zabar, S., Shimoni, E., & Bianco-Peled, H. (2008). Development of nanostructure in resistant starch type III during thermal treatments and cycling. Macromolecular Bioscience, 8, 163−170. Zhang, G., Sofyan, M., & Hamaker, B. R. (2008). Slowly digestible state of starch: mechanism of slow digestion property of gelatinized maize starch. Journal of Agricultural and Food Chemistry, 56, 4695−4702. Zhao, X., & Lin, Y. (2009). Resistant starch prepared from high-amylose maize starch with citric acid hydrolysis and its simulated fermentation in vitro. European Food Research and Technology, 228, 1015−1021.