Impact of Submerged Fermentation Parameters on Proteins Extracted from Ganoderma sichuanense and Their Antioxidant Potential

Ganoderma sichuanense is a widely studied medicinal mushroom, but the production of its antioxidant proteins has been scarcely evaluated. We assess the influence of different concentrations of culture media components under submerged fermentation, with and without agitation, on production of proteins with antioxidant activity from the mycelial biomass of G. sichuanense. Protein extracts were characterized by scanning electron microscopy, X-ray diffraction, and attenuated total reflectance Fourier-transform infrared spectroscopy. They were also analyzed for total protein and phenolic contents, antioxidant activities (ABTS•+, DPPH•, chelating ability, and reducing power), and electrophoretic profiles by SDS-PAGE. The most active extract was tested for cytoprotective potential under H2O2-induced oxidative stress in Saccharomyces cerevisiae. Growth kinetics of the best fermentation condition were also analyzed. Microstructural differences ranged from fibrillar to aggregated forms, depending on cultivation. Crystallinity was unaffected, but chemical differences and secondary structure organization were confirmed by infrared spectroscopy. The extract from the static culture with 10 g·L−1 glucose, 5 g·L−1 yeast extract, and 2.5 g·L−1 soy peptone (referred as CM1S) showed the highest protein and phenolic contents and the strongest antioxidant activity (IC50 = 4.8 and 24.0 µg of protein·mL−1 for ABTS•+ and DPPH•, respectively). SDS-PAGE revealed higher protein band intensities in static cultures. CM1S showed potential to protect yeast cells from oxidative stress. The Gompertz model estimated a specific growth rate of 0.0068 h−1 in CM1S. The findings highlight a cultivation strategy that modulates fungal metabolism and improves the recovery of antioxidant proteins from G. sichuanense biomass.