PATTERNS OF FATTY-ACIDS RELEASED FROM MILK-FAT BY RESIDUAL LIPASE DURING STORAGE OF ULTRA-HIGH TEMPERATURE PROCESSED MILK

Patterns of fatty acids released from milk fat and types of residual lipase activity in UHT milk were investigated. Commercial UHT milk samples obtained immediately after processing were stored at 23 and 35-degrees-C and analyzed for both FFA and lipase activities. Results showed that concentrations of short-chain FFA, except lauric acid, changed little at 23-degrees-C during 12 wk of storage. At 35-degrees-C, however, concentrations of all short-chain FFA showed steady increases, ranging from 9% for caprylic to 45% for lauric acids. Concentrations of long-chain FFA increased moderately (7 to 20%) at 23-degrees-C, but their increases were much higher (26 to 63%) at 35-degrees-C. Patterns of release of FA were similar at both temperatures. However, the ratios of the long-chain FA released in UHT milk were different from those of FA of milk fat. Residual lipase activities were detected in UHT milks as well as in their centrifugal fractions. Cream fractions showed the highest lipase activities, followed by aqueous supernatant and casein precipitates. Cream fractions preferentially hydrolyzed long-chain FA from milk fat, whereas aqueous supernatant fractions hydrolyzed both short-chain and long-chain FA.