Changes in Physicochemical Properties, Volatile Flavor Compounds and Microbiota in Phascolosoma esculenta Muscle During Frozen Storage at −20 °C

Phascolosoma esculenta is a valuable marine seafood, which suffers quality and flavor deterioration with the extension of frozen storage time. To reveal the degradation mechanism, physicochemical properties, microbiota, metabolites, and volatiles were investigated in P. esculenta muscle during frozen storage (−20 °C). Water-holding capacity (WHC) decreased to 77.87%, while the content of total volatile basic nitrogen (TVB-N) and thiobarbituric acid reactive substances (TBARSs) increased to 18.85 mg/100 g and 1.18 mg MDA/kg, respectively. Long-term frozen storage reduced microbial diversity. Macrococcus and Nitrospira became the predominant genera after 360 days of frozen storage, and their predominance was associated with muscle flavor deterioration. Untargeted metabolomics identified 4299 metabolites. Differential metabolites were mainly involved in purine, nucleotide, arachidonic acid, and amino acid metabolism. Volatile profiles were markedly altered during frozen storage. Freshness-related aldehydes decreased markedly, whereas off-flavor alcohols (e.g., 1-octen-3-ol) and sulfur-containing volatiles (e.g., dimethyl trisulfide) continuously accumulated. Pearson correlation analysis showed that physicochemical spoilage indicators, cold-adapted microorganisms, and differential lipid metabolites were closely associated with the generation of undesirable off-odors. This study reveals the interactive effects of protein degradation, lipid oxidation, and microbial succession during frozen storage.