Impact of hydrolysis method and lactase preparation on proteolysis and glycation in long-term stored lactose-hydrolysed UHT milk

Abstract

Shorter shelf-life of lactose-hydrolysed UHT milk (LHM) can be linked to lactase purity both due to unwanted proteolytic activity and Maillard reactions. To study this, pre- and post-hydrolysed milk was added one of three types of lactase enzymes of increasing purity (A, B and C), and stored for up to 1 year at 25 or 35 °C. Proteolytic side-activities in post-hydrolysed milk depended on lactase purity, with lactase A causing the highest proteolysis. The lowest proteolytic activity occurred with lactase C in both pre- and post-hydrolysed milk. LHM with lactase A exhibited proteolysis in C-terminal regions of major milk proteins, particularly in post-hydrolysed milk, which also showed endopeptidase activity. Glycation initiated by UHT treatment was higher in pre-hydrolysed milk than in post-hydrolysed milk, but subsequent storage led to similar glycation levels in both. Therefore, using post-hydrolysis with highly purified lactases, proteolytic side-activities can be lowered and glycation can be delayed.