Optimization of a co-injection process for confectionery systems aided by flow simulation and experiment

Abstract

One-Shot co-injection is an efficient technology for molding filled confectionery products. By simultaneously dosing shell and filling, short processing times in the range of 1 s are achieved. However, the formation of the product is highly dependent on the rheological properties, which requires adaptation of the molding process. Although One-Shot technology is widely used in industry, the process parameters are still adjusted purely empirically. In this work we present a systematic approach for optimizing the One-Shot co-injection process by experimental investigation and flow simulation based on detailed material characterization. Molding is one of the final steps in chocolate manufacturing. Due to the close relation between fluid properties and process conditions, the scope of this work was extended to rheological characterization of confectionery suspensions and analysis of the crystallization behavior of cocoa fat systems. Although the findings from cocoa butter crystallization were not directly incorporated in the One-Shot investigation, they provided valuable information with respect to the precrystallization process which preceeds molding of chocolate. By simultaneously monitoring wide angle X-ray scattering (WAXS) patterns and rheological properties, the crystal formation and transformation in cocoa butter was investigated under steady shear flow conditions. We found that certain triacylglycerols (TAG) fractionated during crystallization. The diffraction patterns provided evidence that crystal form III of cocoa butter is a mixture of a bulk crystalline phase of the form α and a fraction of trisaturated TAGs in form β′. In addition, there were strong indications that the transformation at processing conditions from βV into the most stable crystal form βVI is accompanied by fractionation. The complexity of fat crystallization kinetics was also revealed by quiescent experiments using nuclear magnetic resonance (NMR). In consequence, fraction formation is regarded as an important factor influencing the flow properties of chocolate during manufacturing. With regard to flow simulations, reliable information on the rheology of the phases is essential. Due to the non-Newtonian fluid properties of confectionery suspensions, measuring errors may gain in importance. Rotational rheometry with a vane geometry combined with non-Newtonian shear rate correction produced well reproducible results. The transient nature of the flow properties was relevant with respect to the short process duration. We evaluated different model equations for fitting the flow