Abstract:To investigate the effects of benzalkonium chloride (BAC), a commonly used disinfectant in dairy production, on lactic acid bacteria (LAB) in fermented milk, this study utilized metagenomic analysis to elucidate the mechanisms by which BAC influences LAB gene functions and metabolic pathways. The results revealed a total of 216 LAB species identified from fermented milk samples containing three different levels of BAC, predominantly Streptococcus salivarius subsp. thermophilus, accounting for 99.78% to 98.45% of the total bacterial strains. BAC significantly inhibited the growth and proliferation of LAB. Gene function annotation analysis showed that 16,112 genes were annotated in the COG database, with the highest impact observed on amino acid transport and metabolism functional units. In the KEGG database, carbohydrate and amino acid metabolism were the primary pathways, with gene counts decreasing by 7.76% to 9.1% as BAC concentration increased. CAZy analysis indicated that glycoside hydrolases (GHs) and glycosyl transferases (GTs) were the most abundant enzyme families (accounting for 79.08% to 80.38%), and BAC significantly upregulated the GT8 gene. Differential metabolic pathway analysis demonstrated that BAC downregulated glucose kinase and pyruvate kinase, resulting in reduced acid production capacity in the BAC2.0 sample group, potentially affecting the texture and flavor characteristics of fermented milk. These findings provide critical insights into the potential impacts of BAC on LAB and lay a foundation for further exploration of BAC-related risks in other fermented foods.
