Physicochemical changes and age gelation in stored UHT milk: Seasonal variations

Abstract The physicochemical changes and the occurrence of age gelation during the storage of indirect UHT milk produced in different seasons in New Zealand were examined. UHT milk produced in the early season had the lowest protein and calcium contents, the smallest mean particle size when fresh, and the lowest propensity for age gelation. During storage, the changes in pH, ionic calcium concentration, particle size, and protein profiles of the milk and serum did not vary greatly between the seasons. Protein analysis indicated that the Maillard reaction and limited proteolysis occurred during the storage of UHT milk. The heat-induced aggregation among partially κ-casein-depleted casein micelles might play a part in the physicochemical gelation of UHT milk during storage.