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

The changes in the concentration of monosaccharides and the influence of de phosphorylation 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 degreesC for 120 days. An increase in galac tose and N-acetylglucosamine, together with a decrease in N-acetylglucosami ne-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 an d galactose was examined. While, in most cases, the monosaccharide increase s found were consistent with the disappearance of phosphorylated sugars, ch anges in galactose during storage at 30 degreesC seemed to be due to other processes, probably involving glycosidases, that may have potential detrime ntal consequences to milk stability. (C) 2001 Elsevier Science Ltd. All rig hts reserved.