Contribution of the lactoperoxidase system to the keeping quality of pasteurized milk

The lactoperoxidase system is a naturally occurring antimicrobial system fo und in milk, with lactoperoxidase, thiocyanate and hydrogen peroxide as its components. The keeping quality of milli pasteurized at 72 degrees C for 1 5 s was found to be better than that of milli heated at. 80 degrees C for 1 5 s. This agrees with previous findings and is usually attributed to heat s hocking: of spores. Hoc-ever; complete deactivation of lactoperoxidase occu rred at 80 degrees C-15 s: whereas at 72 degrees C-15 s residual lactoperox idase activity was similar to 70%, which may provide an alternative explana tion. Higher levels of hypothiocyanite (the major antimicrobial agent produ ced by the lactoperoxidase system) were also detected in milk processed at 72 than at 80 degrees C, which supports the theory that the lactoperoxidase system has a role in the keeping quality of pasteurized milk. Of all the m ethods evaluated, titratable acidity and alcohol stability gave the most, c onsistent estimates of keeping quality, while dissolved oxygen was a good i ndication of the onset, of spoilage. Lactoperoxidase activity decreased wit h temperature more rapidly between 70 and SO degrees C than is usual for an enzyme over a 10 deg C range.