Characterization of industrial processed milk by analysis of heat‐induced changes

Abstract

Summary 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 β‐lactoglobulin(β‐LG). Average amounts found were 1710 mg/l of β‐LG and 2.49 μmol/l of HMF in pasteurized milk. In UHT milk, the amounts for direct and indirect processes were 389 and 322 mg/l of β‐LG, 12.0 and 250 mg/l of lactulose and 5.6 and 8.7 μmol/l of HMF. In sterilized milk the amounts were 1120 mg/l of lactulose and 22 μmol/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.