Evaluation of the extent of the Maillard reaction for the quality control of low-heat-treated dairy products [furosine determination].

One of the objectives of the evaluation of heat damage in low-heat-treated dairy products is to characterize them recognizing both overheating processes and use of high-heat-treated raw materials. A well-known modification promoted by heating is the Maillard reaction, the extent of which can be evaluated by furosine determination. A direct HPLC method makes possible the routine quantification of furosine at very low levels and in any type of dairy product. As the Maillard reaction is highly enhanced at low values of water activity, furosine determination should also represent a suitable method for determining dried dairy products both in liquid milk and in fresh cheese. The natural and rather constant furosine value of raw milk (3-5 mg per 100 g protein) is easily exceeded if very low amounts of reconstituted milk powder are present. Milk pasteurization produces a slight Maillard reaction related to the heating conditions. By coupling furosine determination with another heat treatment indicator like the peroxidase test and the content either of soluble serum protein (Kjeldahl) or of soluble beta-lactoglobulin (HPLC), it is possible to identify the maximum level of furosine which can be produced by the thermal process. Low amounts (1-2 per cent) of extra-low-heat reconstituted milk powder added before the heat process are easily recognized in peroxidase-positive pasteurized milk, being the detection sensitivity related to the powder heat class. Furosine values found in commercial milk samples in many cases exceed the expected upper level deriving from the second heat-treatment indicator. These samples being lactulose free (HPLC), addition of sterilized milk can be excluded and the presence of reconstituted milk powder is highly probable (P<0.01). Furosine determination may also be adopted for the quality control of pastafilata and fresh cheese. Industrial cheesemaking of Mozzarella does not produce values of furosine higher than 8 mg per 100 g protein. Data found in several commercial samples from the European market and ranging from 6 to 40 mg show that undeclared use of milk powder or other dried dairy products like casein or caseinate is rather widespread.