The Resistant Starch, Undigestible Energy and Undigestible Protein Contents of Raw and Cooked Milled Rice

The in vitro and in vivo resistant-starch (measured in growing rats) levels were low in five raw rice cultivars differing in apparent amylose content, and the values were correlated positively with amylose content. Cooked and cooked parboiled rices generally had higher resistant-starch contents than raw rices, particularly those with intermediate gelatinization temperature starches, but waxy rice had very low values. Values for undigestible energy, which is mainly in the form of unfermented energy and undigestible protein, were similar in raw rices, but increased with processing, particularly in the higher-amylose rices. In vivo resistant starch was not correlated significantly with undigestible energy and undigestible protein, but undigestible energy and protein were correlated with each other. Parboiling was calculated to increase the resistant-starch content of cooked rice by not more than 1%. Thus, cultivar differences in cooked-starch digestibility were reflected less in levels of resistant starch than in the rate of starch digestion as indicated by glycaemic and insulin response. Copyright 1993, 1999 Academic Press