H: Health, Nutrition, & Food Nutritionally Important Starch Fractions of Rice Cultivars Grown in Southern United States James A. Patindol, Harmeet S. Guraya, Elaine T. Champagne, and Anna M. McClung Abstract: Dietary starches can be classified into 3 major fractions according to in vitro digestibility as rapidly digestible (RDS), slowly digestible (SDS), and resistant starch (RS). Literature indicates that SDS and/or RS have significant implications on human health, particularly glucose metabolism, diabetes management, colon cancer prevention, mental performance, and satiety. In this study, the nutritionally important starch fractions (RDS, SDS, and RS) in cooked rice were assayed in vitro, making use of 16 cultivars grown in 5 southern U.S. rice growing locations (Arkansas, Louisiana, Mississippi, Missouri, and Texas). RDS, SDS, and RS were 52.4% to 69.4%, 10.3% to 26.6%, and 1.2% to 9.0%, respectively, of cooked rice dry weight. Cultivar, location, and cultivar-by-location interaction contributed to the variations in RDS, SDS, and RS contents. Means pooled across locations indicated that SDS was higher for the Louisiana samples than those from Texas, whereas RS was higher for the Texas samples than those from Arkansas, Louisiana, and Mississippi. Some cultivars were identified to possess high levels of RS (for example, Bowman and Rondo) or SDS (for example, Dixiebelle and Tesanai-2) and were also stable across growing locations. Apparent amylose content correlated positively with RS (n = 80, r = 0.54, P ≤ 0.001), negatively with RDS (n = 80, r =−0.29, P ≤ 0.05), and insignificantly with SDS (n = 80, r = 0.21, P > 0.05). RS and SDS were not collinear (n = 80, r =−0.18, P > 0.05); it does not follow that a cultivar high in RS will also be high in SDS, and vice versa. The observed differences in RDS, SDS, and RS among the samples are indicative of wide genetic diversity in rice. Keywords: digestibility, resistant starch, rice, slowly digestible starch, starch Introduction From a nutritional standpoint, dietary starches can be classified into 3 major fractions according to in vitro digestibility: rapidly di- gestible (RDS), slowly digestible (SDS), and resistant starch (RS). RDS is the fraction that is hydrolyzed to glucose within 20 min; SDS is converted into glucose between 20 and 120 min; whereas, RS remains undigested after 120 min (Englyst and others 1992). SDS and RS have significant implications on human health. As re- viewed recently by Lehmann and Robin (2007), SDS goes through a slow but complete hydrolysis in the small intestine and its po- tential health benefits are linked to a stable glucose metabolism, diabetes management, mental performance, and satiety. RS es- capes digestion in the small intestine but is partially or entirely fermented in the colon. It shows promising physiological impact in the prevention of colon cancer, postprandial glycemia and insu- linemia, hyperlipidemia, gall stone formation, and cardiovascular diseases (Sajilata and others 2006). The digestibility of starch in foods is affected by intrinsic (for example, granule shape and crystallite structure) and extrinsic (for example, extent of chewing and presence of other food com- ponents) factors (Englyst and others 1992). Starch granules with MS 20090847 Submitted 9/1/2009, Accepted 3/9/2010. Authors Patindol, Guraya, and Champagne are with USDA-ARS Southern Regional Research Cen- ter, P.O. Box 19687, New Orleans, LA 70179, U.S.A. Author McClung is with USDA-ARS Dale Bumpers Natl. Rice Research Center, Stuttgart, AR 72160, U.S.A. Direct inquiries to author Patindol (E-mail: James.Patindol@ars.usda.gov). The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Dept. of Agriculture or lack of en- dorsement of similar products not mentioned. the A-type (in cereals including rice) X-ray diffraction pattern or crystallite arrangement are generally more susceptible to amylase digestion compared to those with the B-type (in roots and tubers) and C-type (in legumes) (Franco and others 1992; Jane and others 1997; Srichuwong and others 2005). Rice is primarily consumed as whole grains such that extrinsic factors can easily impact the extent and rate the starchy endosperm is digested by amylases. Previous studies pertaining to starch digestibility in cooked rice grains focused mainly on RS but not on SDS (Panlasigui and others 1991; Eggum and others 1993; Tetens and others 1997; Okuda and others 2005; Denardin and others 2007; Zhang and others 2007). Investigations related to SDS were mostly performed on purified rice starch or flour (Mangala and others 1999; Guraya and others 2001; Anderson and others 2002; Shu and others 2006; Benmoussa and others 2007; Shu and others 2007). Cooked-rice RS may vary from 0% to 12%, depending on the sample preparation and method used in the analysis (Eggum and others 1993; Englyst and others 1992; Tetens and others 1997; Sagum and Arcot 2000; Benmoussa and others 2007; Patindol and others 2010). RS isolated from cooked high-RS rice displayed a mixture of B- and V-type X-ray diffraction pattern (Mangala and others 1999; Shu and others 2006). RS content increases after stor- age and the increase is positively correlated with amylose content (Juliano 1992; Eggum and others 1993; Sagum and Arcot 2000). Amylose : amylopectin ratio affected the rate and extent of rice starch digestion in rats fed cooked rice-based diets (Denardin and others 2007). Based on human trials, Panlasigui and others (1991), however, concluded that amylose alone is not a good predictor of cooked rice starch digestibility because rice varieties with similar high-amylose contents can differ in gelatinization properties and other physicochemical properties, which in turn, influence starch No claim to original US government works Journal compilation C  2010 Institute of Food Technologists R  doi: 10.1111/j.1750-3841.2010.01627.x Vol. 75, Nr. 5, 2010  Journal of Food Science H137 Further reproduction without permission is prohibited