Thermal stability of milk glycosidases and their activities in industrial whey preparations

Abstract

Milk sugars are shown to possess health promoting effects and are thus considered valuable food ingredients, especially for infant nutrition. They may, however, be cleaved by heat stable milk glycosidases that remain active post processing. Nine glycosidases (α-mannosidase, α-glucosidase, β-glucosidase, β-glucuronidase, α-fucosidase, NAGase, α-neuraminidase, α-galactosidase and β-galactosidase) were included in this study investigating thermal stability (45 °C to 90 °C) of milk glycosidases, as well as assessing remaining activities of milk glycosidases in five commercial whey-based preparations. Glycosidase activities were measured by assays based on 4-methyllumbelliferone. The study revealed α-mannosidase and β-glucuronidase to be the most heat resistant glycosidases, which were still active after 80 °C/120 s, and 75 °C/30 s, respectively. Particularly, α-mannosidase and α-glucosidase were remaining active in whey protein- and whey fat concentrates after exposure to heat and ultrafiltration. In contrast, almost no glycosidases were active in whey protein isolate or in enriched whey protein products due to their high purity. Isolates can thus be favored over concentrates to avoid glycosidases in nutraceutical and infant products. No α-neuraminidase activity was detected in the whey products, and only low activity of α-fucosidase, which indicate low degradation of bioactive sugars containing the functional residues α-fucose and sialic acid.