Release of galactose and N-acetylglucosamine during the storage of UHT milk

The changes in the concentration of monosaccharides and the influence of dephosphorylation of sugar phosphates thereon were studied in four batches of UHT milk, (two commercial and two experimental batches produced in a pilot plant) during storage at 10–30°C for 120 days. An increase in galactose and N-acetylglucosamine, together with a decrease in N-acetylglucosamine-1P and galactose-1P, were found, which were larger as the temperature of storage increased. The effects of microbial content and thermal treatment on these processes were evaluated. The contribution of dephosphorylation of the phosphorylated sugars to the total increment in N-acetylglucosamine and galactose was examined. While, in most cases, the monosaccharide increases found were consistent with the disappearance of phosphorylated sugars, changes in galactose during storage at 30°C seemed to be due to other processes, probably involving glycosidases, that may have potential detrimental consequences to milk stability.