Dual-Pigmented Rice: A Dual-Pigmented Whole Grain with Enhanced Nutritional and Antioxidant Properties

Abstract

Pigmented rice is valued for its abundant natural bioactive compounds and potential health-promoting properties. In this study, the black rice cultivar Huamoxiang No. 5 (HMX) was used to develop three genetically similar rice lines with distinct pericarp pigmentation. Among them, BRHMX (a dual-pigmented rice accumulating both anthocyanins and proanthocyanidins) and RHMX (a red rice accumulating proanthocyanidins) were generated through hybridization, successive backcrossing, and marker-assisted selection, whereas the white rice line WHMX was derived from a spaceflight-induced mutant of HMX. Comparative analyses revealed that differences in pericarp pigmentation had negligible effects on grain morphology and major nutritional components, including starch, protein, and amino acids. Compared with HMX, BRHMX maintained more than 80% of the anthocyanin content of HMX, while its proanthocyanidin content was 103% higher than that of RHMX. Furthermore, BRHMX exhibited the highest total phenolic content and the highest levels of 31 soluble phenolic acids, together with the strongest chemical antioxidant capacity, as determined by ABTS and FRAP assays. Untargeted metabolomic profiling showed that flavonoids and soluble phenolic acids were the major metabolite classes associated with pericarp color divergence. Integrated metabolomic and transcriptomic analyses further suggested a potential reallocation of metabolic flux between anthocyanin and proanthocyanidin biosynthetic pathways during early pericarp development. Cooking generally reduced the contents of anthocyanins, proanthocyanidins, and total phenolics, as well as chemical antioxidant capacity, although the magnitude of these changes varied among the four lines. Collectively, these findings demonstrate that the newly developed dual-pigmented rice line combines characteristics associated with conventional black and red rice, providing a valuable genetic resource for whole-grain rice product development.