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

Mississippi State University, Mississippi 39762

ABSTRACT

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 > 10⁶ cfu/ml. All samples were heat processed at 149°C for 3 s, then stored at 7.1°C. 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 > 10⁵ to 10⁶ cfu/ml. The data also demonstrated a decrease in protease activity after ultra-high temperature.