Resistant starch in dietary fiber values measured by the AOAC method in different cereals

Total dietary fiber (TDF) was measured by the AOAC method 985.29 using 30 and 60 min of amyloglucosidase incubation. Resistant starch was determined in the TDF residues after gelatinization, dissolution with 2M KOH, and hydrolysis with amyloglucosidase. The cereals analyzed were: commercial samples of rice (white, parboiled, precooked, and brown parboiled); oat (rolled); maize (grits); and wheat (crackers with bran). Varietal samples of white rice with 1, 18, 24, and 30% amylose also were analyzed. The results showed that cereal starches have different resistances to hydrolysis. Oat and wheat starch were completely hydrolyzed after 30 min, while rice and maize starch remained approximate to 42 and 50%, respectively, of TDF values after 60 min. As expected in the varietal rices, when amylose content increases from 18 to 30%, TDF values were significantly higher because of resistant starch. After subtracting the starch content from the TDF values in white rice, results were similar to values obtained by a chemical method that included lignin. Therefore, it is suggested that corrections are necessary not only for protein and ash, but also for starch, especially on starchy foods.