Predicting safety and quality parameters for UHT-processed milks

A spreadsheet was developed to evaluate safety and quality parameters for m ilks subjected to different heating and cooling profiles and holding time c onditions in a continuous heat exchanger. Safety parameters evaluated were lethality (Fo) and microbial inactivation (B*) values; quality parameters w ere chemical change (C*), thiamin loss, lactulose formation, Maillard brown ing and hydroxymethylfurfural (HMF) formation. The spreadsheet was used to predict these parameters for a pilot plant, heating milks at 120-150 degree sC for 4, 27 and 58 s, using its heating and cooling profiles. Milks were p rocessed in the same plant at these conditions and a selection of the milks were analysed to establish the validity of the spreadsheet. All samples wi th a C* value <3 gave a positive Aschaffenburg turbidity. The activation en ergy that gave the best agreement between the predicted and experimental re sults for lactulose was found to be 122 kJ/mol. One set of optimized condit ions for this product was 135<degrees>C for 10 s, giving B* = 1.24 and C* = 0.55. This milk was compared with two others and its sensory characteristi cs were similar to that with a C* of 1.5 but different to that with a C* va lue of 6. Browning was only found to be noticeable in the most severely hea t-treated sample immediately after processing, but would become apparent on storage at 30 degreesC 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 c ooling rates are fixed.