Numerical modeling of heat and mass transfer during foam-mat drying of green banana: Effect of ovalbumin concentrations

Drying is one of the earliest food storage methods and a complex process involving heat and mass transfer simultaneous under unstable conditions, which can make significant changes in chemical composition, structure and physical properties of food. This process increases the shelf-life of food products, reduces the packaging requirements and facilitates transportation by reducing the volume and mass of the products. In this study, the effect of ovalbumin concentration as a foaming agent (1, 2 and 3%) at 70°C with the foam thickness of 3 mm was investigated on foam mat drying of green banana pulp and on the functional properties of produced powder. Also, computer simulation was performed to evaluate the effect of ovalbumin concentration on heat and moisture distributions. Finally, validation of the model was assessed by matching the experimental data with the predicted data. The results showed that increasing the ovalbumin concentration reduced the foam density and enhanced the expansion (overrun), porosity and stability of the foam. Also, by increasing the concentration of ovalbumin from 1 to 2 & 2 to 3%, Tap density, Carr index and Hausner ratio respectively increased and then decreased. Increasing the concentration of ovalbumin caused a decrease in bulk density, on the contrary, absolute density, intra granular porosity and water solubility index of the powder increased. In the study of morphology and microstructure of green banana pulp powder particles using the images obtained from the field-emission scanning electron microscopy (FESEM), it was observed that by increasing the ovalbumin concentration from 1 to 3%, particle sticking to each other increased; Also, it was found that the surface shrinkage of the particles with increasing the ovalbumin concentration from 1 to 2% & 2 to 3% respectively decreased and then increased. The glass transition temperature (Tg) of obtained powders were determined using DSC. The results from experimental and predicted data showed a correlation coefficient of 0.908. This result indicated a good agreement between the experimental and model data. The uniform distribution of heat and moisture during drying resulted in the betterment of qualitative characteristics of the final product in terms of powder moisture content uniformity and increased the final quality of green banana pulp powder.