Physico-chemical changes during processing and storage of UHT milk

Abstract

In this study, physico-chemical and heat induced changes during the preparation and storage of UHT milk were evaluated. Parameters such as pH, acidity, viscosity, sedimentation, colloidal calcium (Ca), colloidal magnesium (Mg), hydroxyl methyl furfural (HMF), lactulose and color value were evaluated. During conversion of raw milk to UHT milk, there was slight increase in viscosity, colloidal Ca, colloidal Mg, HMF, lactulose and colour value, while decrease in pH value was observed. During storage of UHT processed milk there was significant (p<0.001) increase in viscosity, a value, b value, HMF and lactulose content, whereas a significant (p<0.001) decrease in pH, colloidal Ca, colloidal Mg and L value was observed. Increase in acidity, sedimentation content and formation of Maillard browning products adversely affected the quality of UHT milk. These changes were noticed more in UHT processed milk stored at 30°C vis-à-vis 5°C.

Peptidomic Fingerprints of Stored UHT Milk Inoculated with Protease Extracts from Different Pseudomonas Strains Relative to aprX Expression and Visible Spoilage

“…Anema [33] discussed that, while most studies report a decrease in pH in UHT milk during storage, some studies have highlighted a small pH increase in the first weeks of storage followed by a prolonged decrease. pH decrease for UHT milk storage has been previously reported to occur due to various potential contributions from dephosphorylation of casein micelles, breakdown of lactose, precipitation of calcium phosphate, Maillard reactions and proteolysis [34][35][36]. pH decrease was observed to occur in UHT milk inoculated with extracellular extract from P. panacis DSM 18529 after its maximum milk proteolysis was reached at day 21 (Figures 2 and 3), but this relation was not observed for P. weihenstephanensis DSM 29166.…”

Quality of yogurt produced from various types of milk as raw materials

“…When milk is processed, various changes are made that affect the quality of the milk, especially the pH and protein levels [8]. During refrigeration, UHT milk will get thicker and its pH will go down [9].…”