Selenium-biofortified spent yeast cultivated in corn hydrolysate: antioxidant response and biomass production under aerobic and anaerobic conditions

Spent yeast represents a promising opportunity for value-added applications. This study proposes its biofortification as a source of organic selenium (Se)-enriched supplements. Se is an essential component of the glutathione (GSH) system, playing a critical role in decomposing lipid peroxidation products and protecting cellular membranes. We evaluated the effects of sodium selenite (Na₂SeO₃) supplementation on enzymatic activity, oxidative stress markers, and biomass production of Saccharomyces cerevisiae Thermosacc^®, cultivated in corn hydrolysate-a non-synthetic medium that provides a more realistic representation of industrial environments-under aerobic and anaerobic conditions. Antioxidant responses were assessed via glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione S-transferase (GST) activities, while oxidative stress was measured through hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels. Yeasts were grown with 0, 200, and 400 mg L^-1 Na₂SeO₃. The highest enzymatic activities were observed in AE400 (GPx: 5.35 μmol mg^-1, GR: 3.39 μmol mg^-1, GST: 0.035 μmol mg^-1), indicating enhanced antioxidant defenses under aerobic Se supplementation. However, increased Se concentrations also elevated H₂O₂ and MDA levels-especially in aerobic conditions-likely due to intensified ROS generation. Consequently, biomass production and growth parameters declined, suggesting an energy trade-off in which antioxidant defense is prioritized over cell proliferation. These findings highlight Se's dual role as both an antioxidant and a pro-oxidant at elevated concentrations. This study advances understanding of yeast redox biology and supports the integration of Se-enriched yeast production into industrial fermentation as a sustainable strategy for generating high-value functional ingredients for food and feed applications.