Saccharomycopsis fibuligera solid-state fermentation of wheat bran for glutathione enrichment and functional improvement.

Wheat bran (WB) is an abundant and low-cost cereal by-product, but its compact cell-wall structure and high levels of anti-nutritional factors limit its high-value utilization. In this study, a GSH-producing Saccharomycopsis fibuligera strain K2 with broad extracellular hydrolytic activities was selected for wheat bran biotransformation, and its glutathione (GSH)-producing capacity was further enhanced by atmospheric and room-temperature plasma (ARTP) mutagenesis. The resulting mutant 1-7 produced 29.57% more GSH than the parental strain K2 and was subsequently applied to WB solid-state fermentation (SSF). During SSF, the GSH content reached 272.87 mg/kg, corresponding to 5.23-fold that of raw wheat bran. Fermentation was also accompanied by substantial substrate biotransformation, including increased soluble dietary fiber and total phenolic content, decreased insoluble dietary fiber, a 42.95% reduction in phytic acid, and enhanced antioxidant activity. Volatile profiling further showed increased abundances of esters and aromatic alcohols following S. fibuligera fermentation, whereas co-cultivation with Lactiplantibacillus pentosus increased volatile diversity and enriched volatile phenols, particularly 4-ethylguaiacol. Correlation analysis revealed associations between changes in substrate composition and volatile profiles. Overall, S. fibuligera-based SSF enabled the conversion of low-value WB with co-occurring substrate biotransformation, GSH enrichment, and volatile-profile diversification, providing a laboratory-scale basis for the integrated valorization of cereal by-products.