Optimization of High Yield Conditions and Antioxidant Activity of Ganoderma lingzhi Exopolysaccharide Promoted by Vernonia amygdalina Leaf

Exopolysaccharide (EPS) is the main active metabolite of Ganoderma lingzhi in liquid fermentation. In order to increase the content of Ganoderma lingzhi EPS, this study added Vernonia amygdala leaf powder to the fermentation medium, and used single factor experiments and orthogonal experiments to optimize fermentation conditions. Fourier transform infrared spectroscopy was used to characterize the structure of Ganoderma lingzhi EPS, then its antioxidant activity was detected. The single factor experiment found that when the optimal addition amount of Vernonia amygdala leaf powder was 4g/L, the content of EPS increased by 167% compared with the control group. The optimum fermentation conditions of the orthogonal experiment were as follows: Fermentation duration was 12 d, initial pH was 5.0, the rotation speed was 120 r/min, and the addition amount of Vernonia amygdala leaf powder was 4 g/L. Under such a condition, the content of EPS could reach 13.05 g/L. The infrared spectra showed that the major absorption peaks of the Ganoderma lingzhi EPS from the addition of Vernonia amygdala leaf powder were similar to those of the EPS from the control group. The antioxidant activity assay showed that the addition of Vernonia amygdala leaf powder had less effect on the scavenging of ABTS⁺ radicals by EPS, but enhanced their ability to scavenge DPPH radicals, OH radicals, and ferric ion reduction. The results showed that Vernonia amygdala leaf could effectively increase the content of EPS in Ganoderma lingzhi, which provided a new idea for the efficient production of polysaccharides in Ganoderma lingzhi.