Oral processing of micro-aerated chocolates: a computational mechanics, rheological and tribological study
Creators: name: Samaras, Georgios F.
Publisher: name: Imperial College London
Year: 2021

description: The emerging need to reduce the calorific value of foods, while simultaneously improving the consumer perception drives the quest for food structures that satisfy both criteria. Aiming to shed light on the influence that micro-aeration has on the breakdown of chocolate during the early stages of the oral processing, this study focuses on the investigation of the effect that micro-aeration has from a computational mechanics, rheological and tribological perspective. Firstly, several constitutive models are investigated and compared in both the explicit and implicit Finite Element (FE) frameworks and are calibrated using experimental results from mechanical testing conducted in a parallel PhD study. Afterwards, a non-local damage evolution law is presented providing mesh objectivity in both microscopic and macroscopic FE calculations. The constitutive model coupled with the non-local damage model, implemented in an ABAQUS VUMAT subroutine, is then applied in a micromechanical model for the prediction of the elastic, plastic, and fracture properties of micro-aerated chocolate using as input the properties of the non-aerated solid chocolate. Different boundary conditions are employed in both monodisperse and polydisperse dispersion of pores for the estimation of a representative volume element that is used for the estimation of the macroscopic properties. Overall, micro-aeration reduces the elastic, plastic and fracture properties of the chocolate, whereas the polydisperse dispersions provide a better estimation for the equivalent fracture strain at failure. The estimated values are applied in macroscopic FE simulations of the first bite, where the force-displacement FE results match the experimental data obtained by a replicate of the first bite model with 3D printed molar teeth. The forces needed for the fragmentation of chocolate reduce with micro-aeration level as shown from the experiments and validated by the FE simulations, whereas the in-vivo and in-vitro fragmentation studies show that micro-aerated chocolate breaks into more and smaller pieces. Furthermore, the effect of the micro-aeration on the rheological properties of the molten chocolate with and without the influence of artificial saliva is investigated. Micro-aeration increases viscosity values while the storage and loss moduli decrease. From a tribological perspective, a new bench test rig to measure friction in the simulated tongue-palate contact is developed. The test was applied to molten chocolate samples with and without artificial saliva. Friction was measured over the first few rubbing cycles, simulating mechanical degradation of chocolate in the tongue-palate region. The coefficient of friction increases with cocoa solids percentage and decreases with increasing micro-aeration level. The presence of artificial saliva in the contact reduced the friction for all chocolate samples, however, the relative ranking remained the same. Finally, the link between structure, material properties and sensory perception is given through a comparison with data from sensory tests. The current study can be used as a cost efficient tool for the investigation of new food structures that reduce the calorific value while enhancing the taste perception.