SURVIVAL OF LISTERIA-MONOCYTOGENES IN YOGURT DURING STORAGE AT 4-DEGREES-C

Cows' milk was inoculated with ca 10(3) and 10(7) cfu/ml Listeria monocytogenes. After fermentation at 42-degrees-C for 0-5 h, the yogurt was stored at 4-degrees-C. Low and high inocula survived for 48 h and 7 d, respectively; L. monocytogenes cells were not detectable by direct plating or cold-enrichment after 5 and 15 d, respectively. In low inoculum samples, initial pH at the time of refrigeration was 4.9; the final pH at the time of last sampling was 4.2. In the samples with high inoculum the pH decreased from 5.0 to 4.2.