A laboratory-scale contactor for osmotic dehydration of fresh fruits and vegetables

Data from small-scale batch experiments involving osmotic dehydration of green beans in aqueous solutions of sodium chloride were analyzed, and regression models based upon these data were developed. A laboratory-scale contactor was designed and fabricated to allow batch-type osmotic dehydration of fruits and vegetables. The contactor was then employed to dehydrate green beans in sodium chloride water solutions. Effects of processing variables, including salt solution concentration (5%, 10%, 15%, and 20%), solution temperature (10°C, 20°C, and 30°C), and time of exposure (0, 15, 30, 45, and 60 minutes) on the moisture loss and salt uptake of green beans were evaluated. Regression models of moisture loss and salt uptake were also developed. Models based upon both small-scale batch processing and processing in the contactor were compared in terms of parameters in the models. Small-batch treatments removed moisture more rapidly at the beginning of the processing than did processing in the larger- scale contactor. Overall, more moisture was removed and less salt was taken up by the green beans during contactor processing as compared to the small batch processing. Green bean pods could lose 26% their original moisture while taking on 8% salt by weight when immersed in a 20% NaCl solution at 30°C for one hour during processing in the contactor. Differences in results between the two processing methods may be attributable to (1) different mass ratios for the two experiments and (2) physical differences in the green beans used in the two processes.