Evaluation of osmodehydration and vacuum-assisted osmodehydration as pre-treatments during fruit drying process: The effect on drying rates, effective water diffusion and changes in product quality

Abstract

This work evaluates the effect of applying osmodehydration (OD40 at atmospheric pressure) and pulsed-vacuum osmodehydration (ODVP40, at 498 mmHg) as pre-treatments before apple (cv. Granny Smith) drying. The pre-treatments were evaluated in terms of time-dependent free moisture content (MK), drying rates (DR), effective water diffusion (D), product shrinkage and color changes. The ODVP40 pre-treated samples (40 °Brix grape juice at 40 °C) had a higher total soluble solids content (p < 0.05) and lower moisture content (p < 0.05). Drying experiments were performed at three temperatures (50, 60, and 70 °C) and 3.5 m/s air-flow. Page model best fitted the MK (R2 >0.996) and DR (R2 >0.827). A response surface model was used to estimate the Page model parameters as a function of the initial sample's temperature (T) and total soluble solids concentration (SSo). D values (considering product shrinkage) were computed as 3.56–5.48 × 10−10 m2/s, 6.86–14.35 × 10−10 m2/s, 30.70–72.81×10–10 m2/s for fresh, OD40 and ODVP40 apple, respectively.