Quantification of emulsifier adsorption onto sugar crystals dispersed in vegetable oil and associated effects on flow behaviour

Emulsifiers play an essential role in the flow behaviour of confectionery products such as chocolate. This research associated emulsifier adsorption onto sugar crystals and its effects on the flow properties of model sugar-in-oil suspensions. A new method to quantify emulsifier adsorption onto sugar crystals dispersed in oil was developed by exploiting the relationship between oil-water interfacial tension and unadsorbed emulsifier in the continuous oil phase. The model system consisted of 30 wt% sugar-in-oil suspensions to which were added up to 1 wt% soy lecithin, ammonium phosphatides (AMP), citric acid esters of mono- and diglycerides (CITREM) or polyglycerol polyricinoleate (PGPR). The link between sugar crystal surface coverage, sedimentation, aggregation state and apparent viscosity was then investigated. The lecithin, AMP and CITREM showed the largest decrease in apparent viscosity when added to the suspension at 0.05 to 0.1 wt%, which corresponded to their critical micelle concentration. The largest decrease in sugar crystal aggregation and sedimentation was also evident at this emulsifier concentration. By contrast, addition of PGPR led to a continuous decrease in viscosity and aggregation in the sugar suspension as a function of concentration, with no evident optimal concentration observed. Key advantages of this new method are its simplicity and ability to quantify emulsifier concentration in dispersed systems irrespective of emulsifier identity.