Aggregated whey proteins and trace of caseins synergistically improve the heat stability of whey protein-rich emulsions

Abstract

Heat treatments are used to extend the shelf life of manufactured food emulsions, which in turn require excellent heat stability. Whey protein aggregation prior to homogenization is a means to modify emulsion heat stability but the underlying mechanism of heat stabilization has hardly been studied in an industrial context where whey protein ingredients contain caseins. Emulsions were prepared with 30% anhydrous milk fat and 70% whey protein/casein solutions with protein concentrations ranging from 3 to 6%. The proteins were either unheated (WP/Cas samples) or heat-aggregated (A-WP/Cas samples). After homogenization, the fat droplet interface was characterized and emulsion stability was analyzed visually and at microscopic level. WP/Cas emulsions were heat stable at low protein concentrations but exhibited a gradual decrease in heat stability when the protein concentration increased (>3%). This instability was due to the co-gelation of the protein-coated fat droplets and the proteins in the dispersing phase. In contrast, A-WP/Cas emulsions were rapidly heat destabilized at low protein concentrations (<4%) but were more heat stable than WP/Cas emulsions at higher protein concentrations. The stability of the A-WP/Cas emulsions at protein concentrations higher than 4% was correlated with the heat stability of the whey protein aggregates in the dispersing phase and the decrease in the proportion of whey protein aggregates at the oil/water interface due to increasing competition with caseins present in the whey protein ingredient. This study contributes to greater understanding of the functional role of aggregated whey proteins and residual caseins in emulsions stabilized by industrial WP ingredients.