Effects of somatic cell count on quality and shelf-life of pasteurized fluid milk

Milk was collected from eight Holstein cows four times before and four time s after intramammary infection with Streptococcus agalactiae. Postinfection milk had significantly higher somatic cell count (SCC) (849,000 cells/ml) than preinfection milk (45,000 cells/ mi). High SCC raw milk had more lipol ysis and proteolysis than low SCC raw milk. Pasteurized, homogenized, 2% fa t milks from pre- and postinfection periods were stored at 5 degrees C and analyzed for lipolysis, proteolysis, microbial quality, and sensory attribu tes at 1, 7, 14, and 21 d post processing. During refrigerated storage, the average rates of free fatty acid increase (i.e., lipolysis) and casein hyd rolysis in high SCC milk were, respectively, three and two times faster tha n those in low SCC milk. In general, standard plate counts, coliform counts , and psychrotrophic bacterial counts of both the high and low SCC milks re mained low (<100,000 cfu/ mi) during 5 degrees C storage. Low SCC milk main tained high organoleptic quality for the entire 21-d shelf-life period. How ever, for high SCC milk, between 14 and 21 d, sensory defects were detected , which resulted in low overall quality ratings. The sensory defects mainly included rancidity and bitterness and were consistent with higher levels o f lipolysis and proteolysis. Hence, mastitis adversely affected the quality of pasteurized fluid milk. It is recommended that the fluid milk industry consider implementation of premium quality payment programs for low SCC mil ks.