Resistant Starch in Dietary Fiber Values Measured by the AOAC Method in Different Cereals

Cereal Chem. 73(6):759-761 Total dietary fiber (TDF) was measured by the AOAC method 985.29 hydrolyzed after 30 min, while rice and maize starch remained =42 and using 30 and 60 min of amyloglucosidase incubation. Resistant starch 50%, respectively, of TDF values after 60 min. As expected in the was determined in the TDF residues after gelatinization, dissolution with varietal rices, when amylose content increases from 18 to 30%, TDF 2M KOH, and hydrolysis with amyloglucosidase. The cereals analyzed values were significantly higher because of resistant starch. After subwere: commercial samples of rice (white, parboiled, precooked, and tracting the starch content from the TDF values in white rice, results brown parboiled); oat (rolled); maize (grits); and wheat (crackers with were similar to values obtained by a chemical method that included ligbran). Varietal samples of white rice with 1, 18, 24, and 30% amylose nin. Therefore, it is suggested that corrections are necessary not only for also were analyzed. The results showed that cereal starches have differprotein and ash, but also for starch, especially on starchy foods. ent resistances to hydrolysis. Oat and wheat starch were completely Dietary fiber content is one of the interesting nutritive parameters in food. The enzymatic-gravimetric method of Prosky et al (1985), officially known as AOAC method 985.29 (AOAC 1990), has been adopted by government agencies in many countries for routine nutrient labeling analyses because it is simple and rather inexpensive. However, there is some concern that the values for total dietary fiber (TDF) obtained in some foods are higher than those obtained by other enzymatic-chemical methods (Mongeau and Brassard 1989, 1993, 1994). The current AOAC method of dietary fiber determination includes undigested starch in its estimation (Englyst and Cummings 1988, Muir et al 1993, Vollendorf et al 1993, Marlett et al 1994). Several authors consider that analytically enzyme-resistant starch should be included in dietary fiber results because its physiological properties are similar to certain fiber polysaccharides (Theander et al 1994, Prosky et al 1985). However, the amount of this undigested starch would depend not only on the particular characteristics of a starch, such as amylose-to-amylopectin ratio, crystallinity, and gelatinization temperature, among others (Colonna et al 1992), but also on the sample treatment, such as grinding or cooking (Snow and O'Dea 1981). Therefore, the starch amount included in fiber results, might not reflect the true amount of resistant starch in human digestion (Englyst and Cummings 1988). Starchy foods such as cereals might yield the highest results. We have noticed that rice is one of the cereals that shows larger differences among results from different methods. In this article, we describe an improvement to the AOAC method of starch hydrolysis that involves prolonging the incubation time with amyloglucosidase to obtain results closer to those obtained by enzymatic-chemical methods on rice, maize, oat, and wheat. Furthermore, we studied the effect of amylose concentration on the dietary fiber results of rice. Resistant starch was determined on the fiber residues as the total available starch for amyloglucosidase digestion after solubilization with 2M HOK (Champ 1992). 'Department of Food Sciences and Nutrition, School of Pharmacy and Biochemistry, University of Buenos Aires, Argentina. 2 Corresponding author. Fax: 54-1-964-8423. Publication no. C-1996-1004-07R.