Effect of the stabilizers on partial coalescence occurring in cocoa butter-in-water emulsions: a comparative study between sunflower lecithin, buttermilk powder and sodium caseinate

Abstract

The texture of an emulsion comprising crystallized dispersed phase depends on the extent of partial coalescence. The aim of the present work was to determine the effect of three stabilizers on partial coalescence and therefore on the texture of cocoa butter emulsions initially prepared in the oil liquid state and allowed to crystallize for seven days. Partial coalescence was assessed by visual inspection, granulometry and confocal laser microscopy. We show that the type of emulsifier is of utmost importance, everything else being unchanged: dairy proteins are too protective, inhibiting partial coalescence and the formation of a gel, lecithins are not protective enough to lead to interesting gels while buttermilk powder, comprising a mixture of both stabilizers, is very promising since a spreadable gel could be obtained thanks to connections between droplets. Interfacial tension measurements, between water and middle chain triglycerides that are liquid at room temperature, were carried out to highlight the comparative behavior of the stabilizers. Atomic Force Microscopy (AFM) was used to map the interface topography. In the case of buttermilk, the surface was rough with the existence of some protruding crystals responsible for these connections. Wide Angle X-ray Scattering (WAXS) and Small Angle X-ray Scattering (SAXS) were carried out to assess the lateral and longitudinal packing of coca butter triglycerides in the emulsion droplets stabilized by the three emulsifiers. All these results provide an understanding of the origin of the very different textures of the emulsions obtained with the three stabilizers.