Can prior subjection to pre-heating enhance the heat tolerance of mesophilic bacterial cultures?
The enhancement of heat tolerance of mesophilic bacterial cultures is important for withstanding the elevated temperatures in the development of probiotic processed cheeses. The objective was to determine whether prior subjection to preheating would enhance heat tolerance of mesophilic cultures. Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris were suspended in a 0.1% peptone and exposed to the preheat temperatures of 30oC, 40oC, 50oC, 60oC, 70oC or 80oC for 1, 5, or 10 minutes. The cultures were then grown in M17 broth at 32oC for 72 hours. After the first generation of growth the cultures were then subjected to the same preheat temperature and time, and then grown in M17 broth at 32oC for 72 hours. The second generation was also subjected to the same preheat temperature and time and grown in M17 broth at 32oC for 72 hours. After three generations of growth the cultures were then subjected to the challenge conditions of 95oC for 5 minutes. The control cultures were exposed to the challenge conditions without the subjection to any of the preheat temperatures and times. The cultures were plated in M17 agar and allowed to incubate aerobically at 32oC for 72 hours. Three replications were conducted. No growth was obtained when any of the pre heat treated cultures were subjected to the challenge temperature and time conditions. Heat tolerances of mesophilic cultures studied were not enhanced under these conditions.
Keywords: heat tolerance, mesophilic cultures, cheese