Changes of Phenolic Profiles and Antioxidant Activity in Pigment Rough and Brown Rice (Oryza sativa L.) During Germination

This study investigates the alterations in phenolic profiles and antioxidant activity of pigmented rough and brown rice (Oryza sativa L.) during a controlled germination process at 30°C over periods of 12, 24, 36, and 48 h. Our findings indicate a gradual decrease in total phenolic and flavonoid content, as well as antioxidant activity, in both rough and brown rice varieties throughout the germination process. Notably, red and black rice exhibited detectable levels of proanthocyanidins and anthocyanins, respectively, with significantly higher concentrations observed at the initial stages of 0 or 12 h. A comprehensive analysis identified seven phenolic compounds in germinated red rice, including trace amounts of p-hydroxybenzoic acid, and exclusively vanillic acid (14.83-24.91 mg/100 g) in germinated black rice. The levels of p-coumaric, sinapic, and ferulic acids in red rice peaked between 24 to 36 h post-germination. Specifically, these acids increased by 103.8%, 75.3%, and 93.8% in cultivar GRR, and by 61.6%, 54.0%, and 55.8% in cultivar GBR, respectively. This trend is in contrast to black rice, where peak levels of these acids were observed at the un-germinated stage. The germination process was also associated with a reduction in isoferulic acid content in both red and black rice varieties. Our results substantiate that germinated rough rice contains significantly higher levels of phytochemicals compared to germinated brown rice, suggesting its superior potential in germination-based applications. Furthermore, principal component analysis, explaining 92.18% of the total variance, offers valuable insights for the food industry in developing functional grain products enriched with health-promoting phytochemicals.