Effects of Fusarium oxysporum infection on flavor quality and bidirectional metabolic characteristics of dried Lutjanus erythropterus fillets

Dried Lutjanus erythropterus (L. erythropterus) fillets are susceptible to fungal contamination during storage, resulting in flavor deterioration and food safety risks. Fusarium oxysporum (F. oxysporum) has been identified as one of the predominant spoilage fungi in dried L. erythropterus fillets, but its spoilage mechanism remains unclear. This study investigated the effects of F. oxysporum infection on the flavor quality, food safety, and bidirectional metabolic characteristics of dried L. erythropterus fillets. A 40-day storage experiment was conducted using a non-inoculated control group (CK) and an F. oxysporum-inoculated group (FO). Dynamic changes in fungal colony counts, deoxynivalenol (DON), moisture content, and adenosine monophosphate (AMP) were monitored. Free amino acids, volatile compounds, and untargeted metabolomics were analyzed to characterize flavor and metabolic alterations. The fungal population in the FO group increased rapidly and reached a maximum of 260 CFU/g on day 24. DON concentration remained low before day 20 but increased sharply thereafter and stabilized at 12.93-14.47 μg/kg. Moisture content and AMP in the FO group exhibited a three-stage variation pattern of decline, increase, and subsequent decline. Compared with the CK group, umami, sweet, and bitter amino acids increased significantly and reached their highest levels on day 40, with excessive accumulation of bitter amino acids contributing to taste deterioration. F. oxysporum infection reduced desirable volatile compounds, including aldehydes and esters, while promoting the accumulation of spoilage-related amines and pyrazines. Phenylacetaldehyde was identified as a characteristic biomarker, and days 12-20 represented the critical period for flavor deterioration. Untargeted metabolomics revealed significant temporal metabolic differentiation, with 198 metabolites upregulated and 131 downregulated on day 32 compared with day 0. Differential metabolites were mainly enriched in amino acid metabolism pathways, among which tryptophan metabolism was identified as the core pathway. In conclusion, F.oxysporum infection accelerates quality deterioration and increases food safety risks in dried L. erythropterus fillets by disrupting physicochemical properties, amino acid metabolism, and flavor-related metabolic networks. Tryptophan metabolism plays a central regulatory role, and days 12-20 constitute a critical early-warning window for fungal deterioration. These findings provide a theoretical basis for fungal contamination control and preservation of dried aquatic products.