Development of fractional viscoelastic model for characterizing viscoelastic properties of food material during drying

Mechanical properties, specifically, viscoelastic properties of food materials are the most important characteristics which change significantly while drying is in progress. These changes of the viscoelastic properties have a great impact on the deformation of food material during drying. Understanding of the nature of this changing viscoelastic property is crucial for developing a realistic mathematical model for deformation during food drying. The viscoelastic properties of fresh food samples have been predicted using classical models such as Maxwell model and Burgers model. However, due to the diverse nature of food material, these models cannot predict various viscoelastic properties accurately (relaxation modulus, relaxation time, stiffness, coefficient of viscosity and creep compliance) during drying as conditions are continuously changed. In this context, the fractional viscoelastic model is proposed in this study as a new approach for predicting the accurate viscoelastic behaviour for food materials during drying. Therefore, the main aim of this paper is to develop and validate a viscoelastic model for characterizing viscoelastic properties of food material during drying using fractional viscoelastic model. The proposed model is used to capture the changes of the viscoelastic properties of the food materials during drying. Proposed model is validated by comprehensive experiments as predicted results very closely matched with experimental results. It is found that the fractional order (ψ) changes exponentially with the moisture content, whereas the stiffness (χ) shows third order polynomial change with the moisture content. Interestingly, it is found that the material behaviour is dependent on strain rate while applying the monotonic compression load on the fresh apple tissue at different constant strain rates.