Comparative protein digestibility in growing rats of cooked rice and protein properties of indica and japonica milled rices

Eight indica and japonica milled rices with low amylose content and low sta rch gelatinisation temperature were analysed for cooked rice energy and N b alance in growing rats and for protein properties. Digestible energy values were similar. Japonica rices Koshihikari and Sasanishiki had higher true d igestibility (TD) and net protein utilisation in rats than indica rices IR2 4 and PR23383-15. Similar results were obtained from in vitro proteolysis. High TD of cooked rices was not significantly correlated with low prolamin content in raw rice and with low waxy gene (product protein bound to starch granule) but was significantly correlated with low cysteine content in pro tein and with low denatured prolamin content in cooked rice. In two pairs o f cooked waxy milled rices, which are devoid of waxy gene product, japonica rice still tended to show higher rat TD and in vitro protein digestibility than indica rice, consistent with lower cysteine content in japonica prote in. (C) 2001 Academic Press.