Non-Targeted Metabolomics Reveals the Effects of Different Light Cycles on Samsoniella hepiali

This study aimed to investigate the effects of different light treatments on the growth, antioxidant activity, and metabolite profiles of <i>Samsoniella hepiali</i>. Mycelial biomass, bioactive components, antioxidant capacity, and metabolomic profiles were analyzed under dark, continuous light, and 12 h light/12 h dark cycle conditions. The results showed that the 12 h light/dark cycle significantly reduced dry mycelial weight compared to the dark and continuous light groups (<i>p</i> < 0.001), while no significant difference in biomass was observed between the latter two. Polysaccharide (Pol) content did not differ significantly among the three groups. In terms of antioxidant activity, the continuous light group exhibited the highest protein (Prot) content, total phenolic (TP) content, DPPH radical scavenging activity, and ferric reducing antioxidant power (FRAP) as well as the lowest superoxide anion (·O₂^-) content. The dark group showed the highest activities of superoxide dismutase (SOD) and catalase (CAT). Correlation analysis revealed that total phenolic (TP) content was significantly positively correlated with 2,2-Diphenyl-1-picrylhydrazy (DPPH) and FRAP (<i>p</i> < 0.01), and significantly negatively correlated with superoxide anion content (<i>p</i> < 0.05). Non-targeted metabolomics identified 3643 metabolites, primarily amino acids and derivatives, organic acids, and glycerophospholipids. KEGG enrichment analysis indicated significant accumulation of differential metabolites such as linoleic acid, tyrosine, and phosphatidylcholine across comparison groups. These findings provide insights into the regulatory role of light exposure on the antioxidant capacity of <i>S. hepiali</i> and support its further development in fermented mycelial products.