This is caused by the high heat stability of the enzyme (~88%
residual activity) after UHT process conditions (138 C, 18 s). It was
shown that the milk matrix has a protective effect on the enzyme
activity during the thermal process. A further reason for the
spoilage ability is the high enzyme activity with casein as a sub-
strate under the storage conditions of UHT milk. The milk was
spoiled after four weeks of storage even at low enzyme activities
(1 pkat mL1
).