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Application of machine learning (ML)-based algorithms in food drying is an exciting and innovative approach to advance the drying technology. In order to appropriately develop this novel approach i...

Food materials, particularly plant-based food materials, are mostly cellular in structure with diverse structural heterogeneities and variable cellular properties. To uncover the fundamental drying process, the cellular-level understanding of simultaneous heat and mass transfer process and associated morphological changes is essential. Consequently, researchers have attempted to investigate microlevel transport and material properties and their spatial and temporal distribution using recent innovative and cutting-edge experimental methods and technologies. The aim of this paper is to review the latest experimental technologies that can be applied to investigate the micro-level features of food material during drying. A comprehensive overview of advanced experimental techniques including X-ray microtomography, nuclear magnetic resonance (NMR), Near Infrared (NIR) Spectroscopy, light microscopy, nanoindentation and atomic force microscopy (AFM) has been presented. Finally, a summary of the current challenges of micro-level investigation for food drying is presented at the end of this paper.

Effective diffusivity is the most important key parameter needed in the analysis, design and optimization of heat and mass transfer during food drying process. Generally, two types of effective diffusivities are used to develop the mathematical modelling of food drying namely, moisture dependent effective diffusivity (MDED) and temperature dependent effective diffusivity (TDED). However, no study has extensively investigated which effective diffusivity is more accurate in predicting drying kinetics. The main goal of this study is to determine the appropriate effective diffusivity for predicting the drying kinetics. Drying models were developed for different fruits and vegetables based on moisture dependent and temperature dependent effective diffusivities. COMSOL Multiphysics, a finite element based engineering simulation software is used to solve the coupled heat and mass transfer equations. 3D moisture profiles were developed to investigate the spatial moisture distribution during drying. Extensive experimental investigation on five types of fruit and vegetables were conducted and results were compared with the simulated results. The experiments were repeated three times, and the average of the moisture content at each value was used for constructing the drying curves. Close agreement between experimental and simulated results validates the models developed. It was observed that the moisture profile and temperature profile in case of MDED were more closely fitted with the experimental results. For all fruits and vegetables, the moisture ratio with MDED was significantly lower than moisture ratio with TDED. This finding confirms that the MDED is more accurate for predicting kinetics in food drying. Moreover, the moisture ratio of apple was lowest whereas pear showed the highest moisture ratio. On the hand, carrot showed a considerably lower moisture ratio compared to potato.