Effect of micro-aeration on mechanical and thermal properties of chocolate and correlation to oral processing

Abstract

Food oral processing is of great interest to the food industry due to the need for designing foods with controlled sensorial attributes. This study targets to explain stages of oral processing such as first bite, mastication, and melting of chocolate using a combination of engineering techniques, i.e. experimental protocols and computational models. The fundamental goal of this study is twofold; firstly, to link mechanical properties of chocolate to sensorial attributes using sensory experiments for chocolate with varying levels of porosity. Secondly, employ these mechanical properties as inputs to develop computational models that simulate the first bite and chocolate’s melting. Fundamental mechanical experiments were performed to measure the mechanical properties, such as Young’s modulus, fracture stress, and fracture toughness of chocolate with different levels of porosity ranging from 0% to 15%. The micro-porous chocolate samples indicated micro-pores with an average pore size of 40 μm. The outcome of the mechanical experiments showed a significant effect of micro-aeration on these mechanical properties. Material properties such as Young’s modulus, fracture stress, and fracture toughness were found to decrease on average by 30%, 25%, and 40% with 15% micro-aeration. The two-layer viscoplastic model was used in this work to predict the material behaviour of chocolate based on experimentally determined stress-strain curves. To investigate the fragmentation of chocolate, in-vivo mastication experiments were performed on chocolate samples with varying levels of porosity. The number of fragments increased by 75% when the non-aerated chocolate was compared against the 12% micro-aerated chocolate after one chewing cycle. Heat transfer experiments were designed to investigate the thermal behaviour of chocolate and coupled with a multiscale computational model to simulate the melting of chocolate fragments as a function of chewing cycles. In addition, a heat transfer test rig was developed, which could record the thermal changes in chocolate with enough resolution under different thermal loads. The results showed that the thermal conductivity and specific heat capacity decreased and increased on average by 20% and 10% respectively, with 15% micro-aeration, suggesting a slower rate of heat transfer for the micro-aerated chocolate. However, the micro-aerated chocolate melted faster (up to 55%) inside the mouth due to the higher fragmentation, an effect which was aligned with the melting time from the sensory experiments. The measured mechanical properties were used to explain the differences in sensorial attributes observed from in-vivo sensory tests, such as hardness, grittiness, and melting time but also the fact that sweetness perception remained unaffected of porosity. The outcome of this study can lead to the development of a design tool for chocolate products with controlled sensorial attributes and a potential enhancement of their nutritional value.