Milk protein hydrolysates obtained with immobilized alcalase: Antioxidant properties of hydrolysates and milk fat stability

Abstract

This study investigated the catalytic activity of immobilized alcalase in producing milk protein hydrolysates (MPHs), their antioxidant properties, and the stability of their fat. Alcalase was immobilized on three functionalised resins, with the hydrolysis conditions being enzyme to substrate ratio of 1000 units/g of milk, pH 8.0, temperature 50 °C and hydrolysis time of 10 min. Alcalase immobilized on octadecyl-activated resin was found to be more active with multiple reuse properties, retaining 80 % of its catalytic activity after ten reuses. The antioxidant activities of all the MPH produced were tested and were shown to inhibit the oxidative destruction of β-carotene more effectively than the unhydrolysed milk. MPH production was then scaled up in a custom-built enzyme reactor for controlled yield. Milk fat analyses using gas chromatography with flame ionization detection (GC-FID) and Iatroscan-FID showed that the lipid classes and fatty acid compositions of the unhydrolysed milk and MPH remain unchanged. The peroxide value (POV), p-Anisidine (p-AV) and Thiobarbituric Acid (TBARS) tests showed that lipid oxidation occurred more in the unhydrolysed milk compared to the MPH after 18 weeks of storage. This study concludes that immobilization can significantly improve the properties of alcalase and increase the number of hydrolysis cycles that it can perform while being used to produce high-quality MPH with improved antioxidant properties and stable lipids.