Low-Temperature Co-Fermentation of Lactobacillus bulgaricus 134 and Saccharomyces cerevisiae: Effects on Polyphenols Composition, Flavor Compounds and Antioxidant Activity of Black Rice Slurry

Black rice is abundant in polyphenolic antioxidants, but conventional thermal processing degrades these heat-sensitive compounds, limiting their bioactivity. Although single-strain fermentation can improve the extraction of bioactive components, it remains challenging to simultaneously balance the flavor and bioactivity of fermented black rice products. Low-temperature co-fermentation with yeast and lactobacillus has emerged as a promising strategy to enhance both the flavor profile and functional quality of fermented foods. Therefore, this study investigates the effects of low-temperature co-fermentation with Saccharomyces cerevisiae and Lactobacillus bulgaricus 134 on the quality of black rice slurry. The efficacy was systematically evaluated by monitoring fermentation kinetics, conducting polyphenol and anthocyanin metabolomics analysis, performing flavoromics analysis, and combining in vitro ABTS radical scavenging assays with a Caco-2 cell-based oxidative stress model. The results showed that this process activated β-glucosidase within the first 24 h of fermentation. By activating terpenoid and phenolic metabolic pathways, it maximized the accumulation of anthocyanins and short-chain esters during 30–36 h, which conferred the product with prominent fruity and sweet notes. Fermented black rice slurry (FBRS) exhibited potent ABTS radical scavenging activity. In the Caco-2 oxidative stress model, FBRS pretreatment restored cellular viability, upregulated the activity of endogenous antioxidant enzymes, and reduced MDA content. This study provides a theoretical foundation for developing high-nutritional, flavor-enhanced fermented black rice products.