Response surface methodology to optimize the culture conditions of Ophiocordyceps sinensis Based on antioxidant activity

Ophiocordyceps sinensis (O. sinensis) were valuable "food-medicine homologous" fungus with anti-aging and health benefits. In order to obtain O. sinensis with strong antioxidant capacity, we used 7 strains (ZD, LJ, XW, DR, XH, HN, LD) from different regions to optimize the culture conditions using response surface methodology. Metabolomics and transcriptomics were employed to explore the differences in metabolite composition and candidate genes controlling the heterogeneous accumulation of compounds. The strain from the LJ region had the strongest antioxidant properties, and the parameters of the optimal culture conditions were fermentation time of 30 d, temperature of 18, speed of 145 rpm, and inoculum volume of 20%. Response surface methodology showed that the optimum parameters of the medium were beef broth of 50%, peptone of 0.5%, glucose of 3%, yeast paste of 0.1%, KH2PO4 of 0.34%, MgSO4 of 0.13%, at which time the FRAP of O. sinensis in LJ (2.49 +- 0.14 umol Trolox/g) was increased by 35.49% over the original one. LC-MS/MS assay showed that differential accumulated metabolites (DAMs) were mainly enriched in organic acids and derivatives, organoheterocyclic compounds, and lipids. These DAMs were significantly enriched in the pathway with glycerophospholipid metabolism and biosynthesis of unsaturated fatty acids. The transcriptome results showed that differentially expressed genes (DEGs) upregulated in optimization strain (OF) were mainly enriched in the pathways with tyrosine metabolism, valine, leucine and isoleucine degradation, glutathione metabolism and other. Combined analysis revealed that DEGs such as aurF (G6O67_005062), ADH6 (G6O67_006735) and PC-14 (G6O67_004551) complexly regulate the accumulation of heterogeneity of metabolic flows in ascorbate and aldarate metabolism and taurine and hypotaurine metabolism is the main reason for the influence of antioxidant properties in O. sinensis. These findings provide a reference for the effective development of high antioxidant activity in O. sinensis.