Survival of Listeria monocytogenes During the Manufacture and Ripening of Trappist Cheese

Trappist cheese constitutes more than one-third of the semisoft cheese production in Yugoslavia. The ability of Listeria monocytogenes to survive the Trappist cheese-making process and persist during 90 d of ripening and storage was examined. Trappist cheese was manufactured from pasteurized milk (trials A, B, C) and from whey (trials D and E) inoculated with L. monocytogenes (2.46-5.38 log₁₀ CFU/ml). An increase in L. monocytogenes counts was detected after 30 d of ripening in all of the five trials. After ripening and storage for 90 d, the L. monocytogenes counts ranged from 2.72-5.64 log₁₀ CFU/g cheese. A decline in the population of L. monocytogenes was correlated with a decrease in cheese moisture and pH and with an increase in NaCl and titratable acidity.