The Lipase of Pseudomonas fragi III. Enzyme Action in Cream and Butter

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Abstract
The lipase of P. fragi is active in cream from pH 4.9 to 8.2 with an optimum between pH 5.7 and 6.6, using incubation at 36[degree] C for 24 hrs. Growth and lipase production of P. fragi in cream at 15[degree] C for 3 days is slow. However, enough lipase is produced to cause extensive fat breakdown in the cream and the resultant butter. Over 50% of the lipase is not inactivated by pasteurizing the cream at 71.5[degree] C for 30 min. Extensive growth of S. lactis in cream, resulting in lowering of pH, does not appreciably interfere with the growth of P. fragi but markedly reduces lipase production and activity. Butter containing residual lipase undergoes considerable fat degradation during storage, even at -10[degree] C, developing pronounced rancid flavor, especially at 5[degree]C and above.