Effect of an Edible Pectin Coating and Blanching Pretreatments on the Air-Drying Kinetics of Pumpkin (Cucurbita moschata)

Abstract

With the aim of making food drying processing data and their evaluation available, this work entails evaluating the air-drying kinetics of fresh pumpkin slices and those pre-treated by applying an edible pectin coating or blanching. The drying kinetics of the fresh, blanched, and pectin-coated pumpkin slices were evaluated at 60 and 70 °C with air velocities of 0.85 and 1.70 m∙s−1. The effects of the pre-treatments and drying parameters on moisture diffusivity were investigated. Under the drying conditions studied, a constant-rate period was found and the falling-rate period was described by the diffusion equation. In order to take shrinkage into account, shrinkage coefficients were incorporated in an approximate way, using the analytical solution of Fick’s equation. The highest constant drying rate values were obtained for the blanched samples, followed by the coated samples and finally the fresh samples. Constant drying rates demonstrated that this period did not significantly influence the estimate of the effective diffusion coefficients. It was shown that the water diffusivity of the coating was high, but only slightly increased the drying time, thus not affecting drying efficiency. Conversely, blanching promoted more water transfer and enhanced drying efficiency. It was concluded that coating and blanching at the temperatures and velocities studied were promising for use as pre-treatments in the drying of pumpkins.