Bacteriocin characterization of Enterococcus faecium isolates and evaluation of their in situ anti-Listerial activity in Beyaz cheese

Nowadays, as the interest in natural preservatives increases, research on bioprotective cultures that produce bacteriocins and studies on the use of these cultures in foods are also increasing day by day. Present study aimed to investigate bacteriocin characterization and safety of Enterococcus faecium H108, H206 isolates and their potential utilization in the reduction of Listeria monocytogenes ATCC7644 in Beyaz cheese. Enterocin producing E. faecium H108 and H206 strains were isolated from raw cow's milk and identified by 16S rRNA sequencing. Enterocin containing supernatants of E. faecium H108 and H206 were found to be stable to heat various chemicals used in food industry, wide pH range, lysozyme and catalase enzymes. On the other hand, activity of enterocins were inactivated by proteolytic enzymes. Maximum activity of E. faecium H108 was 6400 AU/mL, while that of H206 was 12800 AU/mL, and the activities remained stable for 24 h. Supernatant of both E. faecium H108 and H206 inhibited L. monocytogenes growth in vitro. E. faecium H108 and H206 did not show haemolytic and DN-ase activities and were susceptible to most of the antibiotics tested. The isolates were used in Beyaz cheese and were found to significantly, but not completely inhibit L. monocytogenes growth. The findings of this research suggest that E. faecium H108 and H206 isolates, after a detailed safety assessment, might be employed as bioprotective cultures in Beyaz cheese with starter culture or hurdle technologies.