AFM approach to study the function of PGPR's emulsifying properties in cocoa butter based suspensions

• Use of PGPR in lipophilic suspensions result in enormous decrease in yield value.
• Atomic force microscopy was used to characterize sucrose particle surfaces.
• Effect of PGPR and soy lecithin on sucrose surfaces was examined in detail.
• New findings on mechanism of function of PGPR as an emulsifier are presented.
• PGPR and cocoa butter form loosely bond “pillows” to separate sucrose particles.

Polyglycerol polyricinoleate (PGPR) often is used as emulsifier in chocolate, but only little is known on the specific interactions between sucrose particles, cocoa butter and PGPR molecules. The most remarkable effect of PGPR on lipophilic suspensions is the enormous decrease in yield value compared to soy lecithin which is not yet understood. A combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), rheological measurements and analysis of immobilized fat content was used to reveal more details on the mechanism of function of PGPR.It was found that this mechanism is completely different to the one of soy lecithin. On sucrose particle surfaces, PGPR concentration was determined to 0.18 mg/m2 whereas soy lecithin coverage was calculated to 2.69 mg/m2. The interfacial layer obtained by washing separated sucrose particles with acetone contains 83.6 g/100 g cocoa butter which had been immobilized together with or by PGPR molecules. This interaction plays a major role in the mechanism of function of PGPR as an emulsifier. Weakly bound structures consisting of PGPR and cocoa butter were found to form pillow-like structures. They act as spacers between the sucrose particles and reduce particle-particle interaction so that less structure can be built up. That is why flow can be induced very easily. In addition, as particles move along together very well due to steric hindrance of these pillow-like structures, viscosity of the suspension remains low.

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