Effect of sucrose and sodium chloride on the survival and metabolic activity of Lactococcus lactis under high-pressure conditions

High-pressure processing affects the metabolism and the viability of Lactococcus lactis. Treatments at 200 MPa did not affect the viability of the cells, but reduced their metabolic activity. The analysis of the cells treated at 300 MPa showed that high-pressure initially affects metabolic activity and subsequently damages membrane integrity of Lactococcus lactis. These treatments reduced the number of viable cells by 4 log. Sucrose and NaCl protected the viability of the cells from high-pressure inactivation at 300, 400 and 600 MPa. Sucrose preserved the metabolic activity and membrane integrity of the cells during the high-pressure treatments, salt preserved the membrane integrity, but not the metabolic activity. These results showed that ionic and non-ionic have a different mechanism of protection the micro-organisms against the high-pressure inactivation.