Unraveling the spoilage characteristics and mechanism of Bacillus spizizenii in spiced beef: Insights from in-situ and metabolomics analysis.

Abstract

In this study, in-situ culturing and metabolomics were employed to identify the spoilage characteristics of Bacillus spizizenii isolated from spoiled spiced beef (SB) and to elucidate the metabolic mechanism underlying spoilage. Results showed that within 24 h of inoculation, SB had an off-odor and internal holes, with significant increases in total volatile basic nitrogen, total acid-base reactive substances, and trichloroacetic acid-soluble peptides (P < 0.05). The key off-odor substances were predominantly derived from 2-butanone, 2-heptanone, and 2,3-butanedione, which are associated with lipid metabolism. The formation of holes in the SB resulted from muscle fascicle separation triggered by the degradation of sarcoplasmic proteins and collagen. Metabolomics analysis revealed a significant accumulation of these lipid and protein degradation products (lipid and lipid-like molecules, organic acids and derivatives, and organic heterocyclic compounds), which promoted the activity of lipid metabolism and amino acid degradation in B. spizizenii. Lipid metabolites including arachidonic acid, linoleic acid and butanoate were further metabolized into key off-odor substances. The degradation of sarcoplasmic proteins and collagen by proteases secreted by B. spizizenii might act as a key inducer of amino acid metabolic pathways. In-situ culturing combined with metabolomics provides a comprehensive approach to studying the spoilage mechanism in cooked meat products caused by Bacillus.