Antioxidative flavonoids in adzuki-meshi (rice boiled with adzuki bean) react with nitrite under simulated stomach conditions

Abstract

Non-glutinous rice boiled with adzuki bean (adzuki-meshi) is often prepared in Japan, and the colour of rice in adzuki-meshi is purplish red, suggesting the transfer of adzuki bean components to rice. In fact, red-coloured rice of adzuki-meshi contained adzuki bean flavonoids such as (+)-catechin, (−)-epicatechin, taxifolin, quercetin 7-O-glucoside, rutin, quercetin, and cyanidin-catechin conjugates (vignacyanidins). A salivary component nitrite reacted with the above flavonoids in adzuki-meshi under the conditions simulating the stomach. The reaction resulted in the decrease in the antioxidative components of adzuki-meshi, and the decrease was accompanied by the production of functional compounds like nitric oxide (•NO), 6,8-dinitrosocatechin, 6,8-dinitrosoepicatechin, and 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone from nitrous acid, (+)-catechin, (−)-epicatechin, and quercetin, respectively. In this manuscript, functions of adzuki-meshi are discussed considering the reactions of the flavonoids with nitrite in the stomach.