Lactobacilli isolated from lump sheep's cheeses and their antimicrobial properties

Abstract

A total of 34 strains of lactobacilli were isolated from the lump sheep's cheeses produced from raw sheep milk. The strains were identified by MALDI-TOF MS, and 20 of them demonstrating the best fermentation and sensoric properties in milk were chosen and tested for their antimicrobial activity. All selected strains were active against the indicator bacteria and moulds. The highest inhibitory effect was observed with the strains Lactobacillus paracasei 314, L. paracasei 316, L. plantarum K816, L. plantarum L718, and L. plantarum 2L2. The subsequent research was focused on the metabolites causing this inhibition. The production of lactic and acetic acids was studied under different cultivation conditions (0, 2, 4, and 6.5% NaCl addition; cultivation at 15, 30, 37, and 45°C; and pH value of the broth before sterilisation 5 and 9). L. plantarum L718 produced the highest concentration of lactic and acetic acids under most of the cultivation conditions. Antimicrobial substances such as phenyllactic acid (62.54-101.62 mg/dm3), H2O2 (0.78-2.30 μg/cm3), and diacetyl (produced by L. plantarum K816 and L718) were studied as well.