Effect of ultrasonic vacuum pretreatment on mass transfer kinetics during osmotic dehydration of black jamun fruit.

Abstract

The study investigates the effects of novel combination of ultrasound and vacuum pre-treatment on osmotic dehydration of black jamun fruit. The osmotic dehydration was conducted under three different conditions namely atmospheric osmotic dehydration (AOD), vacuum pre-treated osmotic dehydration (VOD), ultrasonic vacuum pre-treated osmotic dehydration (USVOD). The changes in water and solute content during osmotic dehydration were fitted to Peleg model to predict the equilibrium moisture and solute content values. The adequacy of Weibull distribution model for predicting the moisture and solute contents during osmotic dehydration at different temperatures were assessed. The effective diffusivity of samples in AOD, VOD and USVOD were estimated by application of Fick's second law. The high regression coefficient (R2 > 0.9) and low χ2 value represented the suitability of Peleg model for predicting equilibrium moisture and solute content and Weibull model for predicting both moisture and solute fraction in jamum fruit during AOD, VOD and USVOD processes. Both vacuum and ultrasound vacuum pretreatment enhanced the moisture loss and solute uptake during osmotic dehydration. The results showed the osmotic drying rate was significantly influenced by different pre-treatment techniques and both vacuum and ultrasonic vacuum pretreatment process enhanced moisture loss and solute uptake during osmotic dehydration. The effective moisture and solute diffusivity were highest in ultrasonic vacuum pretreated samples and the values at 30-50 °C temperature were ranged from 8.53 × 10-10 to 9.27 × 10-10 m2/s and 3.81 × 10-10 to 4.39 × 10-10 m2/s respectively. The results were interrelated to changes in tissue structure caused by application of vacuum and ultrasonic vacuum pretreatment.