Lactobacillus paracasei subsp. paracasei strains can increase the safety of artisanal cheeses made from raw milk (intervento orale)

The aim of this study was to select Escherichia coli-inhibiting lactic acid bacteria from among many endogenous strains isolated from two artisanal Calabrian cheeses, Caprino d’Aspromonte and Pecorino del Poro, made from raw goats’ and ewes’ milk, respectively. This was to obtain microorganisms able to improve, without pasteurizing the milk, the hygienic quality of these or other raw milk cheeses. The E. coli-inhibiting activity was detected both in plate and in pasteurized milk.In plate, several lactic acid bacteria, identified as L. paracasei subsp. paracasei, show an intense antagonistic activity against endogenous strains of E. coli. The possibility that the observed activity was due to organic acid or to hydrogen peroxide production was experimentally excluded. The antagonistic effect against E. coli was possibly due to production of bacteriocin-like compounds. Furthermore, the inhibitory substances produced by L. paracasei subsp. paracasei strains have a bactericidal mode of action, as high-lighted by a clearing around the spot of the producer culture. In pasteurized milk inoculated with 0.2% of 24 h-culture of E. coli and then, after 4 h, with 2% of 48 h-culture of the lactic acid bacteria, E. coli was completely eliminated after 8-12 days by L. paracasei subsp. paracasei strains.The described activity is interesting, because it could be possible that, not only E. coli, but also different food-borne pathogens are inhibited, as reported for other lactobacilli. Therefore, artisanal Calabrian cheeses made from raw milk could be protected from E. coli contamination by utilizing selected strains of L. paracasei subsp. paracasei, if need be, together with other lactic starters. The inhibition can be ascribed to the production of bacteriocin-like compounds. The use of L. paracasei subsp. paracasei to increase the safety of cheeses from raw milks seems to be feasible and no adverse sensory changes seem to be observed.