Derivation of two layer drying model with shrinkage and analysis of volatile depletion during drying of banana

Abstract

An existing two layer evaporation/diffusion model of thin layer drying was modified to incorporate shrinkage. The model was developed and tested for a heat pump test dryer using cylindrical slices of banana, which were dried as a single layer. Shrinkage and drying data were collected over a range of conditions from 28 to 38 °C and 12–30% relative humidity. In addition, models of depletion of key aroma volatiles were developed, to allow prediction of aroma profiles under different drying conditions. It was found that inclusion of shrinkage significantly improved the goodness of fit of the drying model, with shrinkage in the direction of slice thickness found to have a greater effect on drying rates than shrinkage in the radial direction. Aroma profiles were compared at different drying intervals, using four banana flavor compounds as indicators. Volatile depletion during drying was found to approximate a first order kinetic reaction with exponential decay over short periods.