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Preserving the Original Activity of Fresh Milk Lipase

1956; Elsevier BV; Volume: 39; Issue: 8 Linguagem: Inglês

10.3168/jds.s0022-0302(56)94827-5

1529-9066

Th. Förster, C. Jensen, Emily Plath,

Diet, Metabolism, and Disease

To properly study lipase activity in milk it is desirable to control the loss in activity of the enzyme that occurs during the first hours of cold storage.This the authors have succeeded in doing by deaerating the milk by nitrogen ebullition.Editor.A rapid decrease in lipase activity during the first hours of cold storage presents a problem to the investigator interested in estimating the lipase content of fresh milk.Peterson et al. (6) observed this phenomenon but also found little additional decrease after 12 hours of aging at 0 ° C.They followed the practice of holding all samples at this temperature for a period of 10 to 15 hours prior to making their lipase determinations.This practice provided samples in which the lipase activity remained reasonably constant.The values they reported for the milk of individual cows, however, do not necessarily reflect the lipase activity of the freshly drawn product.The writers (2) became acutely aware of this problem in connection with the development of a photometric method of estimating milk lipase.4 They repeatedly observed small, but significant, decreases, which were traced to a few minutes difference in the age of the milk.In one experiment involving seven comparisons between fresh and aged (30 hours at 0 ° to 4 ° C.) milk, an average 19% loss in activity was noted.Davies (1) reported that traces of heavy metals, particularly copper, inhibited the action of lipase in unpasteurized sweet cream butter.He suggested that oxidation of the enzyme was partly responsible for the decrease in lipase activity.Krukovsky and Sharp (4) later confirmed the work of Davies.They concluded that dissolved oxygen alone could be responsible for some lipase inactivation.These workers deaerated their milk samples by boiling them under reduced pressure.Apparently the oxygen was almost completely removed by this procedure.Hlynka and Hood (3) deaerated milk samples by ebullition with nitrogen and confirmed the findings of Krukovsky and Sharp.The work of these three groups of investigators indicated that the decreases in lipase activity during cold storage