Studies of Lipase Action. II. The Activation of Milk Lipase by Temperature Changes

Abstract

Lipolysis in cold milk is accelerated by warming the milk slightly and re-cooling. To secure a maximum of activation, milk should be pre-cooled to 5° C. or lower, re-warmed to 30° C., and then re-cooled below 10° C. The length of time the milk is held at the pre-cooling temperature, or at the activation temperature, is of less importance than the actual temperatures employed, at least in the case of moderate rates of heating and cooling.The rate of lipolysis seems dependent upon the crystalline state of the fat, and consequently upon the previous temperature history of the milk. Differences in previous temperature history are retained even at 20° C. for at least 22 hours.Milk which has been activated can be reactivated or deactivated by suitable heat treatment.These phenomena are of practical importance wherever raw milk is handled. It seems probable that this unrecognized phenomenon of activation has been responsible, in part at least, for many experimental results which have been attributed to other factors.