Hazelnut oil migration in dark chocolate - kinetic, thermodynamic and structural considerations

The objective of this study was to assess the effects of three storage temperatures (11, 20 and 26 degrees C) on the migration kinetics and equilibrium states of a model filled confection consisting of dark chocolate and a hazelnut oil-based filling. HPLC, atomic force microscopy and X-ray diffraction were used to study the migration behaviour of hazelnut oil into simulated filled confections and the associated changes in microstructure. Using a Fickean model, the mechanism for the migration of foreign triacylglycerols (TAG) into chocolate was evaluated. Deviations from Fickian diffusion were noted with increasing temperature, and resulted from the breakdown of the chocolate matrix. At higher temperatures, filled dark chocolate exhibited accelerated fat bloom formation due to the increased ingress of foreign incompatible TAG. The rate of migration and the diffusion coefficient increased 20 and 400 times, respectively, when the storage temperature was raised from 11 to 26 degrees C. The amplified rate of migration at elevated temperatures resulted in a confectionary product with a severe loss in quality. There was significant degradation in the texture and gloss of the product within 24 h of storage at 26 degrees C. However, the storage of filled dark chocolate at 11 and 20 degrees C showed negligible deterioration over 8 wk. Overall, the results from this study offer some insight into the optimisation for the production and storage of filled chocolates.