Metabolic and enzymatic changes of Shewanella baltica in golden pomfret broths during spoilage

Shewanella baltica was identified as a specific spoilage organism in golden pomfret. Its spoilage potential and activity have been reported to be closely related to its enzymes. In this work, the main enzymes of S. baltica were reported, and enzyme activities as well as changes of intracellular metabolites of 3 strains (ABa4, ABe2, BBe1) in fish broth during spoilage were determined. Totally, 47 enzymes were identified, amongst which cysteine desulfurase and Lon protease were related to the spoilage potential of S. baltica. Aminopeptidases and endoproteases in S. baltica might make contribution to the spoilage than carboxypeptidases, especially during early spoilage (0–4 d), in which aminopeptidase activity increased by 31.44%–342.01%. In this period, amino acids, organic acids and sugars increased in strain ABa4 and ABe2 (up to 8.73 log1.5 fold change), due to that they were transferred into the cell matrix for bacterial proliferation and activity. In the later spoilage (4–10 d), proteases and nucleotidases were still produced but secreted out of the cell, accompanied by metabolite consumption. The enhanced levels of metabolites in strain BBe1 during later spoilage might be due to a stronger metabolite intake than the consumption. The altered metabolites were mainly involved in amino acid metabolisms, aminoacyl-tRNA biosynthesis and purine metabolism, which were connected with the spoilage activity of S. baltica. This study investigates the spoilage-related enzymes, metabolites and metabolisms of S. baltica, providing information for the spoilage controlling of seafood.