EFFECT OF PROCESSING PROCEDURES ON IN VITRO DIGESTIBILITY AND COLONIC FERMENTATION OF RICEBERRY RICE

Riceberry is a new rice variety which has recently become popular in Thailand and Asia. Cooling cooked rice influences its digestion; however colonic fermentation studies comparing freshly cooked rice (FCR), refrigerated rice (RR) and frozen rice (FR) hydrolysates are limited. Here, in vitro digestion rate and colonic fermentation of freshly cooked Thai riceberry rice prepared by conventional rice cooker (RCM) and boiling method (BM), and reheated after 3 days storage (4 C; RR and -20 C; FR) were investigated. Starch fractions (% wet basis) differed between cooking methods due to varied moisture contents. After storage, resistant starch (RS) contents in RR and FR were not significantly different compared to FCR; however, increase in slowly digestible starch (SDS) was accompanied by reduction in rapidly digestible starch (RDS) in riceberry rice cooked by BM. SDS increased from 7.56% to 16.00% in refrigerated rice (RR-BM) and by 15.81% in frozen rice (FR-BM). Riceberry rice hydrolysates after simulated human upper gut hydrolysis, were not significantly different among treatments and 49.90% escaped hydrolysis. During in vitro colonic fermentation, riceberry rice hydrolysates significantly enhanced probiotic strains; B. animalis TISTR 2194, B. bifidum TISTR 2129 and L. reuteri KUB AC-5 than pathogens; E. coli E010 and S. serovar Enteritidis S003. Colonic fermentation was similar among treatments. Results indicated that cooking riceberry rice by BM and storage reduced starch digestion but colonic fermentation was not dependent on cooking and storage conditions.