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Thermal indicators in milk, which had been subjected to one of the six industrial processes of thermization, pasteurization, direct and indirect UHT-sterilization, pre-sterilization and in-bottle sterilization, were studied. The following three indices of heat damage were analyzed by high performance liquid chromatography (HPLC), hydroxymethylfurfural (HMF), lactulose and acid-soluble ␤-lactoglobulin(␤-LG). Average amounts found were 1710 mg/L of ␤-LG and 2.49 mol/L of HMF in pasteurized milk. In UHT milk, the amounts for direct and indirect processes were 389 and 322 mg/L of ␤-LG, 12.0 and 250 mg/L of lactulose and 5.6 and 8.7 mol/L of HMF. In sterilized milk the amounts were 1120 mg/L of lactulose and 22 mol/L of HMF, without any detectable presence of undenatured whey proteins. On the basis of the time/temperature profiles, a sterilization factor, expressed as seconds, was defined for each thermal treatment. By applying discriminant analysis each industrial process could be classified independently at the 95% confidence level (pasteurization, UHT-treatment and in-bottle sterilization), but direct-UHT treated milk could not be discriminated from indirect-UHT milk, nor thermized milk from raw bulk milk. The simultaneous application of several heat-induced parameters improves the classification of industrial processed milks, and is therefore a useful tool for optimization of the processing conditions.

5-(Hydroxymethyl)-2-furfuraldehyde (HMF) is formed upon heat treatment of milk and milkresembling systems by the Maillard reaction, via its Amadori product, and also by isomerization and subsequent degradation of sugars. Traditionally, the HMF content has been used as an indicator of both degradation routes. A new analytical approach has been developed for determining the HMF formed only by the acidic degradation of Amadori products, called bound HMF, and that could be related to the extent of the Maillard reaction due to heat treatment or long-term storage of foods. Optimal conditions for the acidic digestion procedure were determined. Reversed-phase HPLC is applied for accurate measurement of bound HMF.

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