The effect of drying methods on viscoelastic behaviour of dehydrated fruits and vegetables

Abstract

The effect of drying methods on the rheological behaviour of dehydrated apple, banana, carrot and potato was examined by uniaxial compression tests on cylindrical specimens. Samples were dehydrated using four different drying methods: osmotic, conventional, vacuum and freeze drying. After drying samples at varying final moisture, the contents were tested for compressibility using pressures ranging from 0.02 to 8 kg kg - db. A simple mathematical model was used to describe the viscoelastic behaviour of the examined materials. Four parameters with physical meaning were incorporated in the model: the maximum stress (σ max ), the maximum strain (∈ max ), the elastic parameter (E) and the viscoelastic exponent (p). It was shown that all the parameters were dependent on both the drying method and the material. Osmotic dehydration seems to increase the viscous nature of fruits and decrease their elasticity, while freeze-dried materials seem to have the most elastic structure.