Screening for bacteriocin-producing lactic acid bacteria from kurut, a traditional naturally-fermented yak milk from Qinghai–Tibet plateau

The objective of this study was to screen the bacteriocin-producing lactic acid bacteria (LAB) strains from kurut collected from six regions in Qinghai–Tibet Plateau. Upon the elimination of the effects of organic acids and hydrogen peroxide on tested microorganisms, 5 strains, among a total of 256 presumptive LAB strains screened, belonging to the species of Lactobacillus casei (strains T1, T11 and S9), Lactobacillus lactis (strain S2), and Leuconostoc lactis (strain T14), showed inhibition activities against both Staphylococcus aureus and Escherichia aerogenes. The inhibition activities were destroyed after treated with proteinase K, pepsin and trypsin separately, suggesting the proteinaceous nature of the antimicrobial compounds produced from the strains. The bacteriocins from strains T1 and T14 remained stable for 20 min at 121 °C and after 2 h of incubation at pH values between 3.0 and 11.0, compared with those from strains S2 and T11 that were stable during pH 3.0–6.0, and that from strain S9 stable between pH 3.0 and 9.0. Bacteriocins produced from strains S2, S9 and T11 were resistant to heating treatment at 100 °C for 20 min. Bacteriocins did not adhere to the surface of the producer cells. The results suggest that the extracellular bacteriocins produced from special LAB strains from kurut, of high antibacterial activity, as well as high thermal and pH stability, may be applied to dairy products manufactory to inhibit the growth of spoilage and pathogens during fermentation.