Effects of whey protein aggregation on fat globule microstructure in whipped-frozen emulsions

Four oil-in-water emulsions, stabilized by native or pre-denatured whey proteins in the absence or presence of casein, were whipped at −5 °C and stored at −30 °C for several weeks. The microstructure of these whipped-frozen emulsions, which differed by their protein content, were observed by low-temperature scanning electron microscopy (LT-SEM), and transmission electron microscopy (TEM) following freeze-substitution and low-temperature embedding. Fat globule aggregation and adsorbed protein content in whipped-frozen emulsions were determined after application of thawing, dilution or centrifugation. Micrographs indicated that in aerated products, partial replacement of native whey proteins by pre-denatured whey proteins or casein introduced (i) more homogeneity in air bubble size, (ii) more attachment of fat globules to their air–serum interface, and (iii) fat globules in the continuous matrix that were in closer contact with each other. These differences in the microstructures of whipped-frozen emulsions were attributed to differing surface heterogeneity of adsorbed protein particles to fat globule interfaces.