Blanching effects on convective air-drying and sorption properties of papaya

Abstract

This study investigated the influence of blanching on the drying kinetics of papaya from the perspective of the microstructure of the tissue and the water sorption behavior. Drying kinetics and water effective diffusion coefficients were determined based on Fick’s law considering shrinkage. Intense cellular changes were observed in blanched tissues images obtained by light microscopy and transmission electron microscopy. Heat pretreatment increased the water diffusion coefficients and the drying rates in comparison with fresh fruit. Severe color changes were induced by blanching, resulting in color loss during drying. At intermediate moisture ranges, sorption isotherms of blanched papayas showed lower water sorption capacity than those of fresh fruit, therefore the critical moisture for microbial growth in fresh papayas is higher than in blanched ones. The compensation theory was satisfied for fresh fruit but not for blanched fruit, which presented distinctive sorption behavior attributed to cellular damage caused by heat pretreatment.