A novel bacteriocin RSQ01 with antibacterial activity and its application and metabolomic mechanism in milk preservation

Milk poses a high-risk for microbial contamination (e.g., Salmonella Enteritidis) and spoilage. In recent years, lactic acid bacteria (LAB) bacteriocins have been widely acknowledged as the potential natural antibacterial substance in food biopreservation due to their excellent antibacterial effects. However, studies on the benefits of LAB bacteriocins for maintenance of milk quality were lacking. In the present study, a novel bacteriocin RSQ01 of Lactococcus lactis was purified and characterized extensively. The RSQ01 possessed a molecular weight of 1.90 kDa and an amino acid sequence of GTPSGGADGIGFAFHPEEVG, which exhibited an extensive antimicrobial spectrum against both gram-positive and gram-negative bacteria. Moreover, RSQ01 exhibited excellent tolerance to heat and acid-base treatments, and sensitivity to the proteolytic enzymes, such as trypsin, proteinase K, and pepsin, with a MIC value of 11.63 mu g/mL against S. Enteritidis_35. Furthermore, RSQ01 maintained the nutri-tional composition, antioxidant parameters, and sensory properties of milk. Additionally, 238 differentially abundant metabolites (DAMs) were identified between the RSQ01-treated and-free milk by global metabolomics, which were assigned to eight categories/superclasses (e.g., organic acids and derivatives, lipids and lipid-like molecules, and organoheterocyclic compound). Finally, fourteen metabolic pathways enriched by DAMs were primarily involved in amino acid, lipids, and organic acid metabolism (e.g., phenylalanine/pyrimidine/trypto-phan metabolism, glycerophospholipid metabolism, and C5-branched dibasic acid metabolism). The results provide evidence suggesting that abundance changes in metabolomes caused by RSQ01 contributed to the milk quality. Overall, this study indicated potential of RSQ01 in milk preservation.

Automated summary

Milk is prone to microbial contamination and spoilage, but lactic acid bacteria (LAB) bacteriocins have shown great potential in preserving food due to their antibacterial effects. This study purified and characterized a novel bacteriocin RSQ01 from Lactococcus lactis, which exhibited a broad-spectrum antimicrobial activity against both gram-positive and gram-negative bacteria. RSQ01 also maintained the nutritional composition, antioxidant parameters, and sensory properties of milk, and caused abundance changes in metabolomes, which contributed to the milk quality. Overall, this study highlights the potential of RSQ01 in milk preservation.