Effect of different emulsifiers on the rheology of milk chocolate

Abstract: We investigated the effect of up to 1.5 wt% commercial soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of monoacylglycerols or ammonium phosphatides on the apparent viscosity and microstructure of milk chocolate. A method to quantify emulsifier adsorption onto the dispersed particles in chocolate was first developed. To do so, emulsifier was mixed in the chocolate at different concentrations after which the continuous cocoa butter fat phase was isolated using centrifugation. A force tensiometer was used to measure the equilibrium interfacial tension between water and the extracted cocoa butter fat phase to evaluate the extent of emulsifier adsorption onto the suspended solid particles present in the chocolate system (i.e., sugar, milk powder and cocoa powder). Based on this approach, the PGPR adsorbed the least in comparison to the other emulsifiers tested. The significance of these interactions on macroscopic (apparent viscosity) and microscopic (aggregation behaviour) phenomena were also studied. For all but PGPR, emulsifier addition reduced low shear apparent viscosity and solid particle aggregation behaviour up to a critical concentration, above which there was an increase, implying the presence of additional interactions.
This work suggests that emulsifier molecular weight and head group properties play a role in modifying the interactions between suspended solid particles in molten chocolate.