Bacteriocinogenic Lacticaseibacillus paracasei strains from Inner Mongolian fermented milk efficiently control pathogenic bacteria in model cheddar-like cheese

Abstract

Bacteriocins produced by lactic acid bacteria (LAB) consist of a wide range of antimicrobial proteins or peptides which can be used as bio-preservatives to control food-borne pathogens. In this study, bacteriocinogenic LAB strains were isolated from fermented milk in Inner Mongolia, China. These strains exhibited high antimicrobial activity and were identified as Lacticaseibacillus paracasei. The sensitivity of their antimicrobial activity to protease K implies the possible existence of bacteriocins within the culture. Selected L. paracasei strains were subjected to whole genome sequencing and the bacteriocin biosynthetic gene clusters were identified in-silico. To further verify the antimicrobial properties of the isolated strains in controlling food pathogens in model Cheddar-like cheese, they were used as adjunct starter cultures in cheese contaminated with Bacillus cereus and Listeria monocytogenes. The results showed that each of the five strains carries a minimum of three bacteriocins biosynthetic gene clusters. All L. paracasei strains exhibited the ability to inhibit B. cereus and L. monocytogenes and caused a significant log reduction of pathogens during cheese ripening. Additionally, the isolated strains improved cheese texture and flavor to varying degrees. In conclusion, the indigenious L. paracasei present in milk could play an important role in pathogen control and the quality improvement of Cheddar-like cheeses.