Enzymes ability to serve as markers of pasteurized camel milk

With the increasing number of camel milk dairies being set up in camel breeding areas, reliable tests are needed to evaluate the efficacy of heat treatments, especially pasteurization. Much research has been carried out on the enzymes of bovine milk, but camel milk has different physico-chemical properties and the convenient enzymatic markers are not necessarily the same. A given enzyme can have different heat inactivation kinetics in the two milks, or even be present in one milk and absent in the other. Moreover, the heat treatment needed to pasteurize camel milk probably differs from that generally applied to bovine milk in temperate countries (often 72 C for 15 sec). The generally high temperatures in camel breeding areas, together with the more difficult collection conditions, mean that microbial load before pasteurization is higher. Alkaline phosphatase (EC 3.1.3.1) is the enzyme generally used to test the pasteurization of bovine milk. Gamma-Glutamyltranspeptidase (EC 2.3.2.2.), would be suitable for the detecting heat treatment carried out between 70 and 80°C. Three other enzymes appear to be of interest. In bovine milk, lactoperoxidase (EC 1.11.1.7) can be destroyed completely at temperatures > 75°C, and can therefore be used to detect milk that has been heated above this temperature. Xanthine oxidase (EC 1.1.3.22) was formerly used as an enzymatic marker in pasteurized bovine milk. Leucine arylamidase activity is appreciably higher in camel than bovine milk. This paper permits an estimation of the time-temperature combinations that would be suitable for the pasteurization of camel milk, based on the evaluation of the effect of heat treatments on microbial levels. We also report on the heat sensitivities of the enzymes mentioned above and their suitability for use as markers of pasteurization in camel milk. The standard pasteurization treatment applied to bovine milk at 72°C for 15 sec does not destroy all the aerobic microorganisms in camel milk. However, treatment for 15 or 30 sec at 75 or 80°C resulted in microbial levels of < 4 000 CFU/ ml. These levels remain < 30 000 CFU/ mI after storage at 4°C for 4 days, the current standard limit for pasteurized milk. Alkaline phosphatase remains active after several hours at 75°C, and requires treatment at 90°C for 45 sec to be totally inactivated. Lactoperoxidase and xanthine oxidase are also very heat stable; they are not inactivated after 30 sec treating at 90°C. Glutamyltranspeptidase loses > 70% of its activity after 30 sec treatment at 75°C, and is rendered completely inactive after 16 sec at 80°C. Leucine arylamidase is inactivated at 75°C for 28 sec or at 80°C for 7 sec. (Résumé d'auteur)