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