Effect of psychrotrophic post-pasteurization contamination of the keeping quality at 11 and 5 degrees C of HTST-pasteurized milk in the UK.
The keeping quality of commercial HTST-pasteurized milk and laboratory pasteurized milk from a common bulk raw supply has been investigated for 5 dairies. Spoilage occurred at levels of total bacterial counts around 10(7) colony forming units/ml, but with a slightly higher off-flavour threshold for the commercial milks than the laboratory pasteurized milks. The predominant microflora at spoilage and the type of off-flavour produced differed between the 2 types of milk. Raising the storage temperature from 5 to 11 degrees C caused a slight shift in the spoilage microflora and led to an average reduction in the shelf life of the laboratory pasteurized milk from 28 to 6 d and of the commercial pasteurized milk from 13 to 5 d. Changes in the level of post-pasteurization contamination (PPC) were reflected in changes in keeping quality, particularly at 5 degrees C. However, the greatest improvements were found in the absence of PPC.
D000818:Animals; D001419:Bacteria / Q000254:growth & development*; D002417:Cattle; D003080:Cold Temperature; D004755:Enterobacteriaceae / Q000254:growth & development; D005506:Food Contamination; D005519:Food Preservation / Q000379:methods*; D006358:Hot Temperature; D008892:Milk / Q000382:microbiology*; D006113:United Kingdom