Heat Resistant Bacterial Lipases and Ultra-High Temperature Sterilization of Dairy Products

Abstract

Properties of a heat resistant lipase produced by Pseudornonas spp. MCS0, a psychrotroph isolated from raw milk, were studied to determine if such enzymes could interfere with successful production of ultra-high temperature sterilized dairy products. In milk MCS0 lipase was extremely heat resistant at 100 to 150C and would be expected to suffer little inactivation during recommended ultra-high temperature processes of 121 to 149C for .5 to 8 s. The optimum temperature for MCS0 lipase activity in butter oil emulsion was 40C, and activity at 20 to 25C was 27 to 41% of maximum. The optimum pH was pH 8.5 with only 8.3% of maximum activity at pH 6.5 but 43% of maximum activity at pH 7. Lipase activity was greatest in 5% butter oil emulsions, but activity was never less than 65% of maximum over the range of 1 to 10% butter oil. The pH may be the most critical factor in influencing lipase activity in ultra-high temperature sterilized dairy products. Of five batches of normal whole milk and four batches of