Effect of high pressures on lactic fermentation streptococci in commercial cheese-making starters

The aim of this paper was to determine the effect of high pressure on FD-DVS Flora-Danica and FD-DVS CHN-19 starters. Moreover, the effects of treatment duration (5, 15, 45 and 80 min), the pH of the medium used for multiplication of the cheese-making starters (4,8; 5,6; 6,4 and 7,2) and the initial count of streptococci on the degree of their number reduction during pressurization executed at 200 MPa and 18 degrees C were determined. The highest reduction in the streptococci population was recorded after 80-min pressurization of re-hydrated starter suspensions. However, the most dynamic reduction was recorded in the initial period of pressurization. Further extension of the pressurization duration resulted in further reductions in the dynamics of streptococci inactivation. The initial count of lactic fermentation streptococci in a pressurized starter was found to have a significant effect on the degree of their survivability during pressurization. The pH of the culture used for multiplication of the streptococci of the studied starters also had a significant effect on their bioresistance. The streptococci cultured in pH 6.4 displayed the highest bioresistance to high pressures. Both, an increase and decrease in the culture pH resulted in an increase in the susceptibility of the streptococci to high pressures.