Effect of storage temperature and time on the qualities of pasteurized milk

Abstract

Samples of precooled raw milk and packed pasteurized milk were taken from five dairies. Raw milk was analyzed immediately after sampling. Pasteurized milk was kept at 5±1.0℃, 7±1.0℃, 10±1.0℃, 15±1.0℃, and 20±1.0℃, and analyzed periodically as scheduled until the milk was rejected. 20±1.0℃, and analyzed periodically as scheduled until the milk was rejected. The analysis was conducted triplicately during 6 months. The studied qualities were microbiological, chemical, enzymatic and organoleptic properties. The correlations between microbiological counts and storage time of pasteurized milk at all storage temperatures were linear. The composition of milk was found to be rather constant at all storage temperatures and times. The acidity of milk increased while the flavor scores decreased as storage time increased. The milk was not accepted when standard plate counts reached log 7-9 cfu/ml (colony forming units/ml milk) which related to the acidity>0.2% and flavor scores < 4 (using 1-9 Hedonic Scale). Enzyme protease was not found in raw and pasteurized milk, but the presence of enzyme lipase showed constantly both in raw and pasteurized milk. Shelf-lite of pasteurized milk depended on the storage tempera tures and should not exceed 10℃ At temperature of 5±1.0℃, and 7±1.0℃, pasteurized milk could be kept at least 2 and 1 week respectively.