Applicability of a bacteriocin-producing Enterococcus faecium as a co-culture in Cheddar cheese manufacture

Abstract

Two strains, Enterococcus faecium RZS C5 and E. faecium DPC 1146, produce listericidal bacteriocins, so-called enterocins. E. faecium RZS C5 was studied during batch fermentation in both a complex medium (MRS) and in milk to understand the influence of environmental factors, characteristic for milk and cheese, on both growth and bacteriocin production. Fermentation conditions were chosen in view of the applicability of in situ enterocin production during Cheddar cheese production. Enterocin production by E. faecium RZS C5 in MRS started in the early logarithmic growth phase, and enterocin activity decreased during the stationary phase. The effect of pH on enterocin production and decrease of activity was as intense as the effect on bacterial growth. Higher enterocin production took place at pH 5.5 compared with pH 6.5. The use of lactose instead of glucose increased the production of enterocin, and at higher lactose concentration, production increased more and loss of activity decreased. The production in skimmed milk compared to MRS was lower and was detected mainly in the stationary phase. When casein hydrolysate was added to the milk, enterocin production was higher and started earlier, indicating the importance of an additional nitrogen source for growth of E. faecium in milk. For co-cultures of E. faecium RZS C5 with the starters used during Cheddar cheese manufacture, no enterocin activity was detected during the milk fermentation. Furthermore, the applicability of E. faecium RZS C5 and E. faecium DPC 1146 strains was tested in Cheddar cheese manufacture on pilot scale. Enterocin production took place from the beginning of the cheese manufacturing and was stable during the whole ripening phase of the cheese. This indicates that both an early and late contamination of the milk or cheese can be combated with a stable, in situ enterocin production. The use of such a co-culture is an additional safety provision beyond good manufacturing practices.