COUPLING OF LACTULOSE AND FUROSINE INDEXES FOR QUALITY EVALUATION OF STERILIZED MILK

The lactulose and furosine indices, describing the extent of lactose isomerization and early Maillard reaction (MR), respectively, are widely used to evaluate the heat load in milk sterilization processes. In this work, the combination of furosine and lactulose values for sterilized milk has been used to provide additional information about the ther mal histol ll of the end-product. Samples of UHT milk and in-bottle sterilized milk processed under defined conditions (n = 46) or collected from the market (n = 160) were consider ed The effects of raw milk pH, of addition of reconstituted milk powder, of processing conditions, and of prolonged storage were investigated. A high correlation between lactulose and furosine levels was found for all the milk samples of known origin and freshly prepared. When lactulose (y) was expressed as mgL(-1) and furosine (x) as mg 100g protein(-1), the function of the correlation line,vas y = 3.02 x -41.51, with r = 0.99. High values of milk pH enhanced lactose isomerization but did not affect MR. On the contrary, milk drying only promoted intensive MR. This behaviour was also found after prolonged preheating or long storage of sterilized milk. The presence of reconstituted milk powder ol over heating of milk was identified in some commercial samples of sterilized milk.