ADJUSTING FLOW PROPERTIES OF MOLTEN MILK CHOCOLATE BY MEANS OF EMULSIFIERS AND FAT

Flow properties of milk chocolate were measured at different emulsifier (soy lecithin or polyglycerol polyricinoleate [PGPR]) and fat (cocoa butter) contents. Measurements were carried out using a rotary viscometer equipped with the coaxial cylinders geometry in the shear rate range 5-60/s at 40C. Flow curves at the increasing strain rates were modeled by the Casson-Steiner equation to determine the Casson yield stress (sigma(ca) ) and the Casson plastic viscosity (eta (ca) ). Independently of the fat content (between 31 and 34%, wet basis), sigma (ca) and eta (ca) decreased when increased amounts of lecithin were added to the molten milk chocolate and showed a minimum at a lecithin concentration of 0.4% for sigma (ca) and 0.6% for eta (ca) . PGPR seemed to decrease more significantly sigma (ca) than soy lecithin. The rheological properties of the molten chocolate could be predicted by varying lecithin and fat contents on the basis of a central composite experimental design. The model used was statistically significant (R2 = 0.80 for sigma (ca) and 0.89 for eta (ca) ). PRACTICAL APPLICATIONS Monitoring the flow properties of molten milk chocolate allows the possibility for confectionery manufacturers to optimize their formulations and processes and to minimize cost. Emulsifiers such as soy lecithin and polyglycerol polyricinoleate give the manufacturers more control over the flow properties of the molten chocolate and flexibility in formulation. Cocoa butter is an expensive constituent of chocolate. Its role in modulating the rheological properties of chocolate may be accomplished by incorporating relatively small amounts of certain emulsifiers. It was the aim of this work to study the combined effect of emulsifier and fat (cocoa butter) contents on the rheological properties of molten milk chocolate to provide more understanding on the influence of each constituent on the rheological parameters.