In-situ measurements of drying and shrinkage characteristics during microwave vacuum drying of radish and potato

Drying performance, drying rate, and shrinkage are essential subjects in the field of food drying technology. Microwave vacuum drying at room temperature is well known for high-quality and fast drying of food. This study presents in-situ and continuous measurements of samples' mass and shape without taking out the samples from the vacuum drying chamber. The change of measurement method from ex-situ to in-situ demonstrates that the continuous microwave heating accelerates water transfer from the interior to the surface of the sample with less deformation due to external ambient pressure. Potatoes and radishes are used as samples to examine the water transfer and shrinkage deformation mechanisms during internal heating by microwave irradiation. It is found that decreasing the water content increases the drying rate, before reaching the critical water content. In addition, the glass transition phenomenon in the potato's core significantly reduces the shrinkage rate. • A novel in-situ measurement method was developed for microwave vacuum drying. • In-situ measurements demonstrate reduced shrinkage rate and faster drying. • Microwave internal heating enhances water transfer to the external surface. • MRI images indicate internal dehydration even in the early drying stage. • Internal heating reduces shrinkage and creates cavities inside the sample. • Glass transition occurs in the potato and significantly reduces shrinkage.