Effects of vacuum drying on structural changes of bananas, pineapples, and apples
This work aims at investigating structural changes occurring in vacuum drying (VD) compared with conventional convective drying of bananas, pineapples, and apples, and to find the appropriate thin-layer equation for predicting the drying kinetic of products. Drying experiments were carried out at the drying air temperatures of 100 °C, 110 °C, and 120 °C at 4 kPa. The experimental results showed that the VD method at high temperature for all three types of fruits showed the fastest drying time, lowest degree of lightness, lower shrinkage, more pores, more crispness, and more rehydration ability compared with conventional drying and low-temperature drying. Consequently, the VD at drying air temperature of 120 °C was suggested as the best drying condition. Moreover, six mathematical models describing thin-layer drying were investigated. The Logarithmic equation was considered adequate for describing the thin-layer drying behavior of apples, while the Diffusion approach equation was deemed adequate for bananas and pineapples.