Comprehensive metabolomic and pharmacological analyses elucidate antioxidant mechanisms and flavor profiles associated with red pericarp color protein in cooked brown rice.

Abstract

Red pericarp color (OsRc) protein is the key regulator of red seed coat pigmentation in colored rice. However, its detailed role in regulating the cooking properties of brown rice remains unclear. Here, we evaluated the antioxidant properties and analyzed the metabolite profiles of cooked brown rice. The results showed that wild-type (WT) rice exhibited significantly greater antioxidant activity than the two rc mutant rice varieties. Moreover, the total phenolic and flavonoid contents of WT rice were 2.2-fold and 5.0-fold higher than OsRc knockout. Non-volatile metabolomics analysis via Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) identified 447 differentially accumulated metabolites (DAMs). The changes in metabolite levels in phenylpropanoid, flavonoid, flavone and flavonol, and anthocyanin biosynthesis regulated by the OsRc gene may influence the antioxidant properties of brown rice. Network pharmacology and molecular docking showed that four key antioxidant metabolites, including syringetin and hesperetin, showed stable binding with key targets such as Src through hydrogen and hydrophobic bonds. Meanwhile, gas chromatography-mass spectrometry (GC-MS) identified 122 DAMs, including alcohols, esters, aldehydes, and ketones. Gas chromatography ion mobility spectrometry (GC-IMS) revealed that OsRc promoted the accumulation of heptanal, 2-propanone, isoprene, n-octanal, and 1-hexanol. These findings highlight OsRc's potential in improving the antioxidant functionality and flavor quality of brown rice.