Effect of Raw Milk Quality on Ultra-High Temperature Processed Milk

Twenty samples of commercial grade A raw milk were collected and placed in four categories based upon standard plate count. The effect of raw milk quality on keeping quality of ultra-high temperature milk was determined. Categories were 104, >104, <105, >105, to <106, and >10 6 cfu/ml. All samples were heat processed at 149C for 3 s, then stored at 7.1C. Tests conducted were standard plate count, psychrotrophic count, proteolytic count, Hull test, and trinitrobenzenesulfonic acid test. All samples were tested at 0, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, and 90 d. Statistical analyses of raw milk data showed significant differences among categories for both psychrotrophic and proteolytic counts. Also, there were significant differences in the amount of proteolysis that occurred among categories. Both the Hull test and the trinitrobenzenesulfonic acid test indicated that the samples with <104 cfu/ml had significantly less proteolysis than samples with > l0 s to <106 cfu/ml. The data also demonstrated a decrease in protease activity after ultrahigh temperature.