Abstract
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.
Highlights
Composition of gut microbiota impacts on host health through the supply of nutrients which alter metabolism and interact with host cells (Flint, Duncan, Scott and Louis, 2007)
Mean percentage moisture content of riceberry rice cooked by boiling method was 55.33±0.88 and riceberry rice cooked by rice cooker method was 44.83±0.78
Percentage hydrolysis of refrigerated riceberry rice )RR-rice cooker method (RCM)( were 0.53, 1.09, 2.83, 6.55 and 9.14, respectively, while that of frozen riceberry rice )FR-RCM( were 0.77, 1.19, 2.25, 6.71 and 9.68, respectively. These results suggested that hydrolysis rates of freshly cooked, reheated, refrigerated and frozen riceberry rice in the buccal cavity were similar and reached a maximum of 9.14-10.98%
Summary
Composition of gut microbiota impacts on host health through the supply of nutrients which alter metabolism and interact with host cells (Flint, Duncan, Scott and Louis, 2007). Fermentable carbohydrates that escape digestion in the upper gut and selectively stimulate growth and activities of probiotic bacteria in the colon, resulting in host health benefits, are known as prebiotics (Gibson et al, 2017;Gibson and Roberfroid, 1995). Riceberry rice is a purple-pigmented variety cross-bred from Thai Hom Mali rice, Hom Hin rice and Khao Dawk Mali 105 by the Rice Research Center, Kasetsart University, Kamphaeng Saen, Nakhon Pathom, Thailand This variety is popular in Thailand and its environs due to unique grain characteristics such as fluffy texture, flavor and nutritional value; little is known regarding its digestion and colonic fermentation. Digestion rates of freshly cooked and reheated stored riceberry rice were compared and the impacts of their hydrolysates on colonic bacteria fermentation were assessed
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