5 years ago



Another aspect that was

Another aspect that was discussed during the session is that of the residual alkaline phosphatase activity in pasteurized goat’s milk, and more in particular, the legally acceptable limit value of alkaline phosphatase activity. In a concrete manner, the EU-RL MMP examined the possibility to use for goat’s milk the limit value of 350 mU/l that was set by the EU for cow’s milk. This study showed that the alkaline phosphatase activity following pasteurization of goat’s milk is generally below the limit value set for cow’s milk but that this value is exceeded in goat’s milk coming from two Member States (Marina Nicolas, ANSES, Paris). DG SANCO should now take the initiative for legislation since it has enough information to make a decision. The determination of an activity limit value for cheese made from pasteurized milk was also on the agenda of the workshop. The adoption of a limit value is based upon the inventory of values found in practice and, hence, on the capacity of the laboratories to determine the alkaline phosphatase activity in cheese. In 2009, the EU-RL MMP set up a practical workshop on standard ISO 11816-2 (which was then being reviewed) that includes a description of the reference method for that parameter, with a view to improving the testing capacity of the NRL network. Following that workshop, the capacity of the NRLs to use the method was evaluated by means of an inter-laboratory test. Four out of the 19 participating laboratories did not have a sufficient capacity and were re-briefed and then subjected to an evaluation test. After these two briefing and evaluation sessions, 17 laboratories, among which the ILVO-T&V for the Belgian NRL, were found capable of determining the alkaline phosphatase activity in cheese in a correct way. The list of the residual alkaline phosphatase activity values found in practice may now be completed in order to be more representative of the real situation for cheese in Europe (Marina Nicolas, ANSES, Paris). In the meantime, the EU-RL MMP suggested to adopt a working limit value of 10 mU/g which may later be adjusted if necessary. That value has already been tested on some cheese types. So, the Swiss Agroscope laboratory tested the limit value on a certain number of Swiss cheeses made of cow’s milk, using the reference method very accurately (Charlotte Egger, Agroscope,Liebefeld-Posiux, Switzerland). All cheeses of raw or thermised milk that were examined, showed an activity rate of more than 10 mU/g whereas most of the cheeses made from pasteurized milk had a residual alkaline phosphatase activity of less than 10 mU/g. One soft cheese, Limburger, showed a residual alkaline phosphatase activity of more than 10 mU/g although it was made from pasteurized milk. In that particular case, the superficial flora contributed to the alkaline phosphatase activity that was measured: when the activity was measured after removal of a thicker rind (exceeding the standard thickness for that cheese, i.e.0.5 cm instead of “as thin as possible”), it was indeed less than 10 mU/g. The importance of the place,where the sample was taken, was then shown by means of large wheels (80-100 cm diameter) of cheese made from thermised milk: the wheels are so big that the cheese at the centre of the wheel stays warm long enough to deactivate alkaline phosphatase in the same way as in the case of pasteurisation. Whereas for Swiss cheeses, an adjustment of the standard seems at first sight sufficient to make the proposed limit value acceptable, this is not so for other cheese types. As a matter of tact, the EU-RL MMP showed that the manufacturing process of some cheeses may be at the origin of a change in alkaline phosphatase activity and may lead to a misinterpretation of results (Marina Nicolas, ANSES, Paris). During the manufacturing process of mozzarella type cheese e.g., alkaline phospatase is sometimes deactivated, leading to an activity of less than 10 mU/g, although this cheese is made from raw milk. The participants’ attention was also drawn to the opposite phenomenon: cheese made from pasteurized milk that showed an alkaline phosphatase activity of more than 10 mU/g. In the latter case, an activity rate of more than 10 mU/g was measured at the centre of the cheese and not only on the surface, such as in the case of Limburger cheese; so, removing a thicker rind does not solve the problem. It is very likely that the microflora is at the origin of this abnormally high alkaline phosphatase activity. As for the analysis, the ISO 11816-2 method for determining alkaline phosphatase in cheese still needs to be validated. In that respect, the EU-RL MMP intends to carry out a preliminary study on the characterization of the method in 2011 and to deal with the inter-laboratory aspects of validation in 2012. In order to check pasteurization of milk of other animal species (such as camels), the use of other alkaline phosphatase markers, such as lactoperoxidase of γ-GT, is being considered. 34

Reference Ninane V. & Werbrouck H. (2010). Workshop of the NRLs for Milk and Milk Products, Paris, 2010. Labinfo AFSCA, 5, 25-27. 35

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