Effect of seasonal variation on some physical properties and heat stability of milk subjected to ultra-high temperature and in-container sterilisation

• Stability of milk to ultra-high temperature (UHT) and in-container sterilisation was compared throughout 1 year.
• Effects of adding CaCl2, and stabilising salts were quite different for the two processes.
• Heat stability following ultra-high temperature (UHT) was greater in autumn and winter than in spring or summer.

Heat stability was evaluated in bulk raw milk, collected throughout the year and subjected to ultra-high temperature (UHT) or in-container sterilisation, with and without added calcium chloride (2 mM), disodium hydrogen phosphate (DSHP, 10 mM) and trisodium citrate (TSC, 10 mM). More sediment was observed following in-container sterilisation (0.24%) compared with UHT (0.19%).Adding CaCl2 made the milk more unstable to UHT than to in-container sterilisation, while adding DSHP and TSC made the milk more unstable during in-container sterilisation than to UHT processing, although TSC addition increased the sediment formed by UHT processing.Better heat stability was observed in autumn and winter than in spring and summer following UHT. However, following in-container sterilisation, samples with added stabilising salts showed significantly improved heat stability in autumn, whereas with added CaCl2, the best heat stability was observed in spring. No correlation was found between urea and heat stability.