The Science of Colour in Rice: A Review on Health Benefits, Genetic Regulation, and Anthocyanin Stability

The pigmented rice types, i.e., black, red, and purple rice, are highly nutritious substitutes for the ordinary white rice, providing compounds such as anthocyanins, flavonoids, and proanthocyanidins. These bioactive compounds confer antioxidant, anti-inflammatory, anti-cancer, anti-diabetic, and cardiovascular-protective effects, while also assisting in weight management, gut health, and metabolism. The genetic basis of pigmentation includes regulatory genes like OsC1, OsDFR, and OsMYB, which comprise the MYB-bHLH-WD40 complex regulating anthocyanin biosynthesis. Anthocyanin pathways interact with flavonoid and proanthocyanidin synthesis, which is essential for colouration and stress adaptation. The environmental factors, such as temperature, pH, and storage conditions, cause degradation of anthocyanins. Acylation and encapsulation are techniques used in preserving anthocyanins better for industrial use. However, degradation of anthocyanins remains unexplored. Emerging evidence shows that degradation is not only chemical but also enzymatically regulated, mediated by polyphenol oxidases, peroxidases, and β-glucosidases, which accelerate oxidation and hydrolysis reactions and contribute to organ-specific pigment loss. Studies confirm first-order kinetics of anthocyanin breakdown under heat, alkaline pH, and oxygen, while stability improves with encapsulation, co-pigmentation, and gamma irradiation. This review explores the pigmentation of rice (Oryza sativa L.), focusing on its respective health benefits, genetics, synthesis, and degradation. Additionally, much remains to be discovered about its genetic and molecular basis. The regulation of vacuolar enzymes and degradation-related genes in rice tissues is still poorly understood, representing a major knowledge gap compared with biosynthesis.