Modulating the gel strength of filled whey protein hydrogels by altering oil droplets characteristics: Theory and experiments

Protein-based hydrogels are used in a wide range of food products, including desserts, confectionary, dressings, spreads, and meat analogs. For many applications, it is important to modulate the textural attributes of the hydrogels so that they meet consumer expectations. In this study, the impact of oil droplet characteristics, especially size and concentration, on the rheological properties of filled whey protein hydrogels was examined. The experimental measurements were compared to the predictions made by a theoretical model for the elastic properties of filled composite materials consisting of non-dilute spherical fluid particles dispersed within a solid matrix. This theory predicted that the mechanical strength of filled hydrogels can either increase or decrease with increasing oil droplet concentration depending on the size of the droplets. Small droplets have a high Laplace pressure, which makes them more resistant to deformation. Consequently, they may increase the gel strength when their effective rigidity is higher than that of the surrounding protein network. In contrast, large droplets have a low Laplace pressure, which makes them highly susceptible to deformation. As a result, they tend to reduce the gel strength. In this study, we prepared oil-in-water emulsions with different mean droplet diameters and then used them to form heat-set whey protein gels with a range of droplet and protein concentrations. The theory and experiments showed good qualitative agreement but there was a poor quantitative agreement, which was attributed to the fact that the real emulsion gels did not conform to the assumptions used to derive the theoretical model. Even so, this mathematical model is useful for understanding and predicting the behavior of filled food gels.