Effects of Different Temperatures on Flavonoid Secondary Metabolites and Antioxidant Activities of Paecilomyces hepiali

To explore the physiological and metabolic response mechanism of Paecilomyces hepiali (P. hepiali) under varying temperatures, five temperature gradients were established in this study. Combined with in vitro antioxidant assays and untargeted and targeted metabolomics analyses, the variations in antioxidant system and flavonoid secondary metabolites were investigated. Results showed that temperature significantly affected the accumulation of active substances and antioxidant capacity, including of peroxidase (POD), total flavonoids, soluble protein and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Metabolomics analysis revealed distinct metabolic profiles among groups, and flavonoids and phenolic acids were identified as pivotal responsive metabolites. KEGG enrichment analysis revealed that flavonoid biosynthesis, linoleic acid metabolism and arachidonic acid metabolism served as core regulatory pathways. Nineteen common differential flavonoid metabolites were screened out. Correlation analysis revealed that vanillin, cryptochlorogenic acid and sinapinic acid strongly correlated with antioxidant capacity, acting as key regulators for temperature-induced antioxidant responses in P. hepiali. This study verified that temperature modulates the antioxidant system and flavonoid metabolism of P. hepiali, offering references for industrial optimization of its fermentation.