Effects of high-pressure carbon dioxide on Escherichia coli in nutrient broth and milk.

Bactericidal effects of high-pressure carbon dioxide against Escherichia coli were studied under 100, 75, 50 and 25 bar at 20 degrees C, 30 degrees C and 40 degrees C. E. coli suspended in nutrient broth (NB, pH = 6.75) was inactivated under 100, 75, 50, and 25 bar CO2 treatments for 50, 65, 100, and 140 min at 30 degrees C, respectively. Acidification of nutrient broth by dissolved CO2 alone might account for the bactericidal effect under pressure. E. coli was inactivated in NB with initial pH 5.50 and 4.5 at 100 bar for 80 and 95 min, respectively. Treatment at 100 bar CO2 pressure for 6 h caused a decrease of 6.42 and 7.24 log cycles in whole and skim milk, respectively.