Creation of textured dairy emulsions by connecting oil droplets through whey protein aggregates
Résumé
Heat treatment applied on whey proteins solutions causes protein denaturation and induces the formation of aggregates of different sizes and shapes depending on the experimental conditions. Even if cold gelation of whey protein aggregates is well known [1], their role in emulsions and their interfacial properties are less studied. Recent works showed that emulsions containing 30% of milk fat can be textured by modulating the ratio Aggregates (Ag)/Native Whey Protein (NWP) and by taking into account the size and the distance between droplets [2]. Based on these results, our challenge in this study was to texture emulsions with low oil volume fractions using aggregates
We investigated the texture of dairy emulsions composed of 5-30% (w/w) of milk fat stabilized by a mixture of fractal aggregates having an average size of 240 nm and NWP. After homogenization (500 bars), emulsions were analyzed at 20°C by visual observation, granulometry, confocal laser microscopy and dynamic oscillatory measurements. When oil content was 30%, emulsions were already textured after homogenization at 60°C which is in contrast with 5% oil-in-water emulsions that remain liquid. Surprisingly, these low oil content emulsions texturize over time with increasing firmness. It is suggested that Ag allows the formation of a network by connecting oil droplets leading to emulsion texture. Tuning the Ag/NWP ratio induces very different textures for these low oil content emulsions ranging from heterogeneous systems exhibiting syneresis for 2 and 0.1% (w/w) of Ag and NWP respectively to smooth and stable emulsions for 3% of Ag and the same proportion of NWP. Confocal laser microscopy evidenced a rough microstructure with serum pores for emulsions with 2% of Ag and 0.1% (w/w) of NWP (Figure 1A) whereas more homogeneous systems were observed for 3% of Ag (Figure 1B). Moreover, rheological properties of these emulsions are recovered after shearing that could be very interesting for food application perspectives (Figure 1C).
In conclusion, tuning Ag/NWP ratio can be a tool to control and guide emulsion texture even at low oil volume fraction by creating a network. In this way, fractal aggregates may be an alternative to additives use in dairy emulsions