Spoilage potential of pasteurized milk microbiota

The aim of this study was to evaluate the spoilage patterns of pasteurized milk microbiota. Additionally, the microbiological quality of raw and pasteurized milk regarding total aerobic and psychrotrophic counts was assessed. Samples were collected from two dairies at the milk reception point and different sites along pasteurized milk production line. Total aerobic and psychrotrophic counts in raw milk samples from Dairy 1 and 2 were at similar levels (approximately 6-7 log CFU/ml). The pasteurization step significantly reduced the total mesophilic bacteria counts. Samples from both dairies did not contain a detectable level of culturable psychrotrophic bacteria before the filling. However, psychrotrophic count in milk packages from Dairy 1 increased from 0.66±0.26 log CFU/ml to 3.76±0.19 at the end of the shelf-life. Forty-eight isolates with the different colony morphology selected from plate-count agar plates were screened for spoilage potential under laboratory conditions. The most prominent enzymatic trait (64.58% isolates) was proteolytic activity. Out of 17 enzymatically active isolates, 10 isolates were successfully identified as following: Bacillus pumilus (n=3), Bacillus licheniformis (n=2), Leifsonia aquatica (n=2), Pseudomonas oryzihabitans (n=2) and Bacillus megaterium (n=1). More stringent hygiene is required at each step of the dairy production chain to achieve a high microbiological quality of raw and pasteurized milk and to control spoilage microbiota. Book of Proceedings