CHEMICAL PROCESS PARAMETERS FOR THERMAL INACTIVATION OF ALKALINE-PHOSPHATASE IN MILK

Alkaline phosphatase [EC 3.1.3.1] belongs to over 60 indigenous enzyme s in raw bovine milk. This enzyme is important in thermal processing o f milk because a negative result of the phosphatase test is generally regarded as a reliable criterion of correct pasteurization. The paper reports on a comparative study to determine the dependency on the meth od applied of the borderline between a positive and a negative result of the phosphatase test on heat treated milk. The periods at different temperatures and times necessary to produce various degrees of phosph atase inactivation in milk are given. The degree of inactivation chose n for the decision ''phosphatase - negative'' is not a given chemical process parameter but related to the detection limit of the method app lied. The milk samples were obtained in a pilot plant for the indirect milk heating. The temperature-time conditions were chosen in the rang e 60-80 degrees C and 4-128 s covering, thus, the processing condition s for thermization and holder as well as short time pasteurization. Th e paper describes chemical process parameters for thermal denaturation of this milk enzyme. Although the two methods applied (DIN 10 337: 19 93 and ISO 11816-1: 1997) differ strongly in their ALP-sensitivity as well as concerning the specificity of the different substrates used in both phosphatase tests the chemical process parameters for thermal in activation of alkaline phosphatase (tau(1/2), D-, z- and Q(10)-values) were found to agree well. The borderlines between positive and negati ve regions of ALP activity demonstrate that the STH-pasteurization are a is mainly (with respect to the DIN 10 337 method) and completely (co ncerning the ISO 11816-1 method) in the ''phosphatase positive'' regio n. The results of the study were supported by random milk samples (STH -pasteurization) from the market which showed positive phosphatase res ults when the ISO method was applied. Therefore, for use as a criterio n of STH-pasteurization the degree of ALP inactivation has to be fixed at a level sufficient for a correct STH-pasteurization from a hygieni c point of view.