Factors affecting the sensitivity of mesophilic Lactobacilli to high pressure treatment

Resumen del póster presentado al Simposio "Tecnologías emergentes de interés para la industria alimentaria" (EMERTEC), celebrado en España en marzo de 2002.The effects of physiological age of cells and of several factors such as, the growing and immersion media, and temperature during pressurization, on the barosensitivity of Lactobacillus casei ssp casei IFPL 99 and L. plantarum IFPL 935 were studied. Whey permeate enriched with 15% bovine reconstituted skim milk (10%) and 0.5% yeast extract (WPYM) and MRS were used as growth media. Each experiment involved inoculating the whey permeate (WP) and reconstituted bovine skim milk (SM) without incubation and exposing lactobacilli suspensions to pressures up to 400 Mpa for 20 min. The hydrolytic activity of the pressurized cells on the fragment 193-209 of the B-CN (C-peptide) as a index of effectiveness of their peptidolytic enzymes was also considered. Highest sensitivity to high pressure was obtained for logarithmic growth phase cells. Both strains were more sensitive to high pressure when the cells have been grown in MRS than in WPYM. The use of SM as immersion medium had a protector effect for the strains. Higher reductions of viable cells was found at 35 ºC than at 10 and 25ºC in both logarithmic and stationary growth phase cells. High pressures increased the hydrolytic activity of sublethaly damaged lactobacilli on the carboxyl-terminal fragment from B-casein (C-peptide), which contributes to bitterness in cheese. The results of the study could be useful to design the optimal pressure process to obtain cells to use as a cheese ripening agent.Peer reviewe