Predicting safety and quality parameters for UHT-processed milks

A spreadsheet was developed to evaluate safety and quality parameters for milks subjected to different heating and cooling profiles and holding time conditions in a continuous heat exchanger. Safety parameters evaluated were lethality ( Fo ) and microbial inactivation ( B *) values; quality parameters were chemical change ( C *), thiamin loss, lactulose formation, Maillard browning and hydroxymethylfurfural (HMF) formation. The spreadsheet was used to predict these parameters for a pilot plant, heating milks at 120–150°C for 4, 27 and 58 s, using its heating and cooling profiles. Milks were processed in the same plant at these conditions and a selection of the milks were analysed to establish the validity of the spreadsheet. All samples with a C * value < 3 gave a positive Aschaffenburg turbidity. The activation energy that gave the best agreement between the predicted and experimental results for lactulose was found to be 122 kJ/mol. One set of optimized conditions for this product was 135°C for 10 s, giving B * = 1.24 and C * = 0.55. This milk was compared with two others and its sensory characteristics were similar to that with a C * of 1.5 but different to that with a C * value of 6. Browning was only found to be noticeable in the most severely heat-treated sample immediately after processing, but would become apparent on storage at 30°C and above. The spreadsheet is useful for comparing the characteristics of products from plants with different heating profiles or as a means for optimizing UHT plant performance where the heating and cooling rates are fixed.