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

The lactulose and furosine indices, describing the extent of lactose i somerization and early Maillard reaction (MR), respectively, are widel y used to evaluate the heat load in milk sterilization processes. In t his work, the combination of furosine and lactulose values for sterili zed milk has been used to provide additional information about the the r mal histol ll of the end-product. Samples of UHT milk and in-bottle sterilized milk processed under defined conditions (n = 46) or collect ed 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 betwe en lactulose and furosine levels was found for all the milk samples of known origin and freshly prepared. When lactulose (y) was expressed a s 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 a lso found after prolonged preheating or long storage of sterilized mil k. The presence of reconstituted milk powder ol over heating of milk w as identified in some commercial samples of sterilized milk.