Functional properties of milk proteins as affected by enzymatic oligomerisation

Milk proteins were enzymatically modified by transglutaminase, lactoperoxidase, laccase as well as glucose oxidase and analysed for changes in molar mass distribution, techno- and tropho-functional properties.The study revealed that high degrees of protein cross-linking were not only detected upon enzymatic modification of milk proteins by transglutaminase, but also upon incubation with oxidoreductases like lactoperoxidase, laccase as well as glucose oxidase. Due to different reaction mechanisms, oligomeric (20,000–200,000 g/mol) and polymeric (>200,000 g/mol) reaction products with different functional property profiles were synthesised. In contrast to transglutaminase-treated milk proteins, e.g., lactoperoxidase-treated milk proteins performed outstanding interfacial properties and glucose oxidase-treated milk proteins higher in vitro digestibility. Oxidoreductase-treated proteins were shown to exhibit increased antioxidative capacity. Laccase was demonstrated to generate oligomeric as well as polymeric protein/protein and protein/phenolic acid reaction products.The study characterises enzymatically cross-linked proteins and makes it possible to specifically select modified proteins for industrial applications according to the requirements towards food proteins, weighing changes in techno- and tropho-functional protein properties.