Effect of cooking temperature on alkaline phosphatase in the production of raw-milk Pecorino cheese

The alkaline phosphatase (ALP) test is used in many countries as the standard assay for rapid validation of the milk pasteurization process. In Protected Designation of Origin cheeses, ALP has been adopted as an antifraud tool to control the use of pasteurized milk in the production of raw-milk cheeses. Low levels of ALP (<10 mU/g) might indicate the use of pasteurized milk. However, the temperatures adopted during cheesemaking may inactivate the ALP enzyme. To this purpose a trial was carried out where different temperatures of “scotta”-whey were used for the second cooking of Pecorino cheeses after molding for 3 h: T35, T60, T70, T80, T90, and T100. Cheeses’ temperatures were monitored every 15 min during cooking and every 30 min after cooking until ambient temperature was reached. For each temperature treatment, 2 cheeses (1 right after cooking and 1 cheese after cooling at ambient temperature) were sampled for chemical analyses and ALP determination using a fluorimetric method, at both, side (ALPs) and core (ALPc) portions. For both ALPs and ALPc, T80, T90, and T100 cheeses had ALP contents significantly lower (P < 0.001), compared with other treatments. In T70 treatment there was a significant portion effect, with a greater reduction in the side portion compared with the core (2389,4 vs 725,9 mU/g). This might be due to the longer exposition at a temperature above 50°C on the side portion compared with the core (135 min vs 15 min, respectively). The ALP reduction in T70 treatment for core and side portion was 50% and 7% respectively. Despite the use of raw milk, ALPs values found in T90 and T100 were similar to ALP values reported in pasteurized milk cheeses. Care must be taken in using the alkaline phosphatase to control the use of pasteurized milk in the production of PDO cheeses without considering all the temperature related parameters of the cheesemaking process.