Osmotic dehydration and freezing as a suitable pretreatment in the process of vacuum drying kiwiberry: drying kinetics and microstructural changes

Abstract

This study investigated the effects of osmotic dehydration and freezing on the kinetics and microstructure of vacuum-dried kiwiberry. Both fresh and previously frozen fruit were dehydrated in sucrose, maltitol and xylitol. Freezing and osmotic dehydration were selected as possible ways to improve the drying kinetics and positively influence the taste of the fruit. This experiment focused on the analysis of microstructural changes induced by applied processing methods using the X-ray microtomography technique. The results showed that the fruit pretreated in sucrose suffered the least structural damage as expressed by the largest condensation of small pores and thin cell walls. Freezing and xylitol resulted in the accumulation of larger pores and thicker walls. The most rapid drying time of 678-688 min was observed for unfrozen samples, dehydrated in sucrose and maltitol. Freezing slowed down the drying process, by 60-100 min, in comparison to the unfrozen samples. The applied mathematical models proved useful in predicting the kinetics of the drying process. The equation proposed by Midilli et al. provided the best fit for predicting the kinetics of the process.