SENSORY AND MICROBIAL QUALITY OF MILK PROCESSED FOR EXTENDED SHELF-LIFE BY DIRECT STEAM INJECTION

Heat treatments of milk between 100 and 145 degrees C produce a new ty pe of product with a shelf life of 15 to 30 days at 7 degrees C, which is termed extended shelf life (ESL) milk. Little information is avail able on the safety and sensory qualities of this product. Extended she lflife milk is being processed commercially to expand the distribution area of fluid milk products. After arrival at market, this product st ill has the shelf life of a pasteurized product. In this study milk wa s processed by direct steam injection at temperatures between 100 and 140 degrees C for 4 or 12 s. Holding time did not significantly affect the sensory quality of the milk. A trained taste panel found cooked f lavor and other off flavors varied significantly with increasing proce ssing temperature and storage time. There were no significant differen ces noted in cooked or off flavors between 132 and 140 degrees C. Psyc hrotrophic Bacillus species were isolated from milk processed at and b elow 132 degrees C, while no organisms were isolated from milk process ed at temperatures at or above 134 degrees C. Consumer preference pane ls indicated consumers preferred milk processed at 134 degrees C for 4 s to ultra-high-temperature (UHT) processed milk, although there was a slight preference for high-temperature short-time processed (HTST) m ilk compared to milk processed at 134 degrees C for 4 s. Higher temper atures had a less destructive effect on lipase activity, while storage time did not significantly affect lipase activity.