Effect of low frequency ultrasound on lactose-protein interactions in protein solution containing different casein to whey protein ratios

Milk systems containing varying casein-whey ratios (80:20, 60:40, 50:50, 40:60, 20:80) and lactose concentrations similar to those of bovine milk underwent ultrasound at 20 kHz for 1, 5 and 10 min. The influences of low-frequency ultrasound on the physicochemical, structural, thermal and water mobility properties of lactose/protein systems were examined. The physiochemical properties, protein structural changes, water mobility and lactose crystallisation behaviour were mainly a function of the type of protein, the ratio of proteins and the sonication time. The particle size, turbidity and pH values of all milk systems decreased with the increase in sonication time. A higher proportion of whey in the system decreased the lactose crystallisation temperature without sonication. FTIR results indicated that the addition of lactose to the milk system delayed the protein-protein aggregation until 5 min of sonication. The study highlights the interaction of milk components in model milk protein and lactose solutions as a function of milk protein type and sonication that can be utilised in improving the functional and storage properties of food products fortified with milk proteins and lactose as ingredients.image