Lactoperoxidase is an enzyme present in milk in very big quantity. It is associated to the serum proteins. It is inactivated by thermal treatments with considerably high temperatures (70° C for 15 minutes or 80°C for 30 seconds) that are conditions more drastic then those required for a normal pasteurization process. For this reason, the persistence of lactoperoxidase activity in pasteurized milk can be used as a good indicator for the quality of the product. A “light” temperature treatment that preserves this enzyme can be done only to a raw milk of good microbiologic quality. In this case chemical-physical and nutritional characteristics of the milk are altered at the minimum level.

The different sensitivity to heat of some enzymes (in particular alkaline-phosphatase and lactoperoxidase) has permitted the development different methods to be used to verify the efficiency of thermal treatment of milk through pasteurisation. These methods anyway are quality method and only indicate the presence or absence of the enzyme giving only an indication about the fact that a thermal treatment has occurred. A quantitative result of lactoperoxidase though makes possible to determine the nutritional quality of the milk: the higher is lactoperoxidase value, the lower are the alterations of the original

In order to have lactoperoxidase evidence in milk we need to add hydrogen peroxide and a compound that receives the oxygen, to act as an indicator. FOODLAB innovative method permits to quantify the lactoperoxidase in milk in a very easy and quick way. It is used a pre-filled single use cuvette and microquantities of the sample.

Materials:
· FOODLAB Instrument
· Pre-filled single use cuvettes
· Chromogen bottle
· Starter reagent bottle
· Micropipette for taking 5 mL
· Micropipette for taking 50 mL

Prepare the reagent contained into the cuvette adding 50 mL of chromogen reagent. Using the specific pipette add 5 mL of sample into the cuvette and then, after 5 minutes of incubation into the specific cells of the instrument, put 50 mL of starter reagent. After 5 minutes the instrument prints out the result expressed as U/L of lactoperoxidase.

The quantitative analysis of peroxide is an innovative test and therefore it is very difficult to find commercial samples to be used as standards or official reference methods. CDR has compared the analysis of different milk samples done with Foodlab method with the values reported in the technical sheet of the Reflectoquant® reflectometric method.

* Refllectoquant® Peroxidase test in Milk - Reflectometric determination after conversion of a specific substrate

The values have been compared and the results are good. Values reported for tests done with Reflectoquant®:

Values obtained with Foodlab method in CDR laboratory:

In order to verify the specificity of the test it has been done some recovery tests, adding to milk without peroxidase, incremental quantities of raw milk.

The results are very good.

Repeatability tests with Foodlab method have been done in CDR laboratories. The results are very good.

CONCLUSIONS
FOODLAB method for peroxide test on milk is very simple, quick and reliable. The quantitative method gives precise indications about the thermal treatment of milk and in addition is an indicator of milk quality: the higher is the peroxidase value, the lower is the importance of the alterations of the original characteristics that it has encountered.