Growth-Death Kinetics of Listeria Monocytogenes in Strained Yogurt

Abstract

In this research, viability of Listeria monocytogenes was studied in strained yogurt (Turkish name: Torba yogurt) samples prepared in laboratory conditions and contaminated with various levels of L. monocytogenes before and after incubation. When strained yogurt samples (pre-incubation inoculation, A1 and post-incubation inoculation, B1) were contaminated with a 106 cfu/ml level of L. monocytogenes, their pH value reached to 4.08, and the presence of L. monocytogenes was defined only by using the enrichment method at the 30th day of the storage at the pH of 3.55, since the resistance of the bacteria had been lost in those yogurts. However, L. monocytogenes was completely inhibited at the 7th day of the storage for the strained yogurt samples (pre-incubation inoculation, A2 and post-incubation inoculation, B2) contaminated with the level of 104 cfu/ml when the pH value was 3.58. As a result, it can be stated that viability of Listeria monocytogenes may not be possible if the pH of the yogurt is around the ≤3.59 after the 7th day of the storage.