Effect of Emulsifiers on the Rheology of Molten Milk Chocolate

Candidate: Enea Lelaj
Supervisor: Dr. Derick Rousseau

Abstract

Food emulsifiers play an important role in the processing of confectionery products by helping to reduce the apparent viscosity of molten chocolate during mixing and moulding. A range of emulsifiers are presently used in the confectionery industry, with soy lecithin the standard for most applications. Other emulsifiers, notably polyglycerol polyricinoleate (PGPR), ammonium phosphatides (AMP) and citrated esters of mono and diglycerides (CITREM) have also been used in different applications. The mechanism underpinning emulsifier effects on viscosity reduction has yet to be fully elucidated, with most efforts based on experiments on sugar-in-oil suspensions rather than chocolate compositions. It is generally accepted that emulsifiers adsorb to the surface of sugar dispersed in oil thereby limiting particle-particle aggregation. Yet, other than sugar, chocolate also contains cocoa powder and milk powder, which may influence the efficacy of food emulsifier adsorption. The purpose of this thesis was to correlate the viscosity-reducing effects of commercial soy lecithin, PGPR, CITREM, and AMP added up to 1.5 wt% in molten chocolate with its adsorption behaviour. We developed a method to quantify emulsifier adsorption onto dispersed chocolate particles using the relationship between interfacial tension and concentration of unadsorbed emulsifier in a model chocolate. Findings from this approach were then used to provide insights on how emulsifier adsorption was affected by molecular structure and, ultimately, its effects on the flow behaviour of the chocolate. In brief, addition of commercial soy lecithin, CITREM, and AMP reduced low shear apparent viscosity and solid particle aggregation behaviour up to a critical concentration, above which these increased. The apparent viscosity and aggregation response of chocolate containing PGPR did not show a minimum, but gradually decreased with a continued increase in emulsifier concentration. Findings from the present work suggest that emulsifier molecular weight and head group play an important role in modifying the interactions between suspended solid particles in molten chocolate.