Untargeted Metabolomic Analyses of Fermented Unpolished Black Rice with Melanogenesis Inhibition Activity”

Abstract

Fermentation of rice can enhance the release of bioactive ingredients and generate diverse microbial metabolites, contributing to various functional properties. Previous studies have demonstrated that a mixture of selected microorganisms—referred to as the De-E11 starter, composed of Rhizopus oryzae, Saccharomyces cerevisiae, Saccharomycopsis fibuligera, and Pediococcus pentosaceus—produces fermented unpolished black rice sap (FUBRS) with melanogenesis inhibition activity. To further understand this fermentation process, we characterized FUBRS and profiled its metabolite composition in comparison with unfermented unpolished black rice (Un-FR), recognizing the substantial enzymatic activity of the FUBRS microorganisms and their potential for extensive metabolite production. The results indicated that fermentation decreased the pH, increased total acid content, and elevated reducing sugar levels. Moreover, significant alterations in phytochemical profiles were observed in FUBRS. In terms of biological activity, fermentation significantly enhanced antioxidant and tyrosinase/melanogenesis inhibitory activities. Untargeted metabolomic analysis using orthogonal projections to latent structures discriminant analysis (OPLS-DA) revealed a clear differentiation in metabolite profiles between FUBRS and Un-FR. Volcano plot analysis (≥2-fold change) showed a general increase in metabolites—including sugars, phenolic acids, organic acids, and fatty acids—after fermentation. Quantitative analysis confirmed the accumulation of p-hydroxybenzoic acid, lactic acid, acetic acid, and succinic acid, all of which are known melanogenesis inhibitors. This study provides valuable insights into the characteristics and metabolite profile of FUBRS, informing strategies for optimizing fermentation processes to enhance the production of melanogenesis and tyrosinase inhibitory compounds. Moreover, it identifies key metabolites as critical biomarkers for monitoring and controlling these processes. Together, these findings support the efficient and reproducible production of high-efficacy ingredients for cosmetic, nutraceutical, and potentially pharmaceutical applications. © 2025 Sangkaew et al. Distributed under Creative Commons CC-BY 4.0