Combined hot-air and microwave-vacuum drying for improving drying uniformity of mango slices based on hyperspectral imaging visualisation of moisture content distribution

Drying uniformity is one of the most important indicators in evaluating a drying technique as well as the final quality of dried products. In the current study, three drying approaches (hot-air drying (HAD), microwave-vacuum drying (MVD), and the combined method (HAD + MVD)) were applied to dehydrate mango slices. During the HAD + MVD process, the time required for hot-air drying was determined in terms of colour variations during hot-air drying. With the help of hyperspectral imaging in conjunction with multivariate data analysis and image processing, the moisture content distribution on mango slices subjected to different drying methods was visualised. Results showed a non-uniform drying property for mango slices dried by HAD or MVD individually, where HAD-dried samples had a higher moisture content in the centre but MVD-dried samples showed the opposite result. Drying uniformity was improved when HAD and MVD were combined, which produced dried products with an even moisture distribution. Mango slice samples dried by HAD + MVD showed a porous structure and a high percentage of colour retention. The current study led to the development of an effective combined HAD + MVD technique for enhancing drying uniformity for the industry.