Improving the heat stability of whey protein microgel-emulsion with a small quantity of casein.

Whey protein (WP) emulsions are sensitive to heating. Currently non-dairy additives are added to impede emulsion instabilities, but manufacturers are looking for their removal (clean label tendency). WP microgels are highly stable to heating1. They were suggested to be more efficient than native WP to stabilize emulsions over time2, but the heat stability of such emulsions is not addressed yet. Fractal aggregates are responsible for emulsion flocculation and coalescence when they cover fat droplet surface3. Emulsion instability is reduced in the presence of small amount of caseins. We hypothesized that it is possible to design WP emulsions that are stable to heating in a large range of protein concentrations by covering fat droplet surface with caseins and releasing WP microgels in the aqueous phase.Dairy emulsions at 30% fat content and containing between 2.5% to 6.5% (w/w in the aqueous phase) WP microgels, and 0 to 0.4% (w/w in the aqueous phase) caseins were reconstituted. The protein interfacial amount and composition were determined immediately after emulsion formation and the heat-stability of the emulsions at 120°C was assessed at macroscopic and microscopic scale. At low casein concentration in the emulsion the fat droplet surface was mainly covered by WP microgels and the emulsions gelled rapidly on heating. Emulsions were heat-stable at 0.4% casein concentration whatever the WP microgel concentration in the aqueous phase. This study shows that it is possible to produce WP emulsions that are stable to heat treatment in the absence of additives by a reasoned approach: the selection of the casein concentration in order to cover fat droplet surface and the selection of WP aggregates (microgels), that are heat-stable in solution.