Influences of Blanching and Freezing Pretreatments on Moisture Diffusivity and Quality Attributes of Pumpkin Slices During Convective Air-Drying

In this study, the relationship between moisture diffusivity in convective air-drying and cellular structure through blanching and freezing pretreatment and quality attributes of dried pumpkin slices were evaluated to obtain necessary information for designing appropriate drying and pretreatment conditions. The results suggest that the loosely bound structure of cell walls due to blanching and pores in the tissue formed by ice crystals during freezing increased moisture diffusivity. In addition, the functional and structural damage of cell membranes by the pretreatments, shown by the electrical impedance analysis, is likely involved in moisture diffusivity during drying. In particular, the sample pretreated by both blanching and freezing showed significantly higher values of moisture diffusivity compared to other samples. With regards to quality attributes, a decrease in color lightness due to starch gelatinization during blanching dramatically affected the color characteristics of the dried product. Starch gelatinization due to blanching and the formation of pores during freezing significantly influenced the structure of the samples after drying, which affected the rehydration rates and mechanical properties.