Abstract:
In this study, the drying kinetics, ascorbic acid degradation, and color change kinetics of kiwifruit during hot air drying (HAD), vacuum drying (VD), freeze drying (FD), and hot air-microwave-assisted vacuum combination drying (HA-MVD) were investigated. The applicability of Weibull model for describing the rehydration kinetics of dried kiwifruits was also assessed. The ascorbic acid content of the kiwi fruit decreased by 77.52, 75.41, 39.86, and 29.64%, and the total phenolic content decreased by 26.62, 29.24, 19.16, and 1.99% after HAD, VD, HA-MVD, and FD, respectively. For all drying processes, the ascorbic acid degradation was best described by the Weibull model. Zero-order, first-order, and combined kinetic models were examined to fit data of color parameters (L*, a*, and b*). Scanning electron microscopy images of the dried products were also obtained. The results indicate that HA-MVD may be an alternative method for the drying of kiwifruit since it provides good quality product in shorter time.
Practical applicationsKinetic modeling of changes in foods during drying is an important issue in relation to predicting quality changes and setting optimal processing conditions. In this study kinetic models describing the ascorbic acid degradation and also the color change of kiwifruit during four different drying methods were determined. Kiwifruit contains high amount ascorbic acid which is widely considered as a marker of nutritional quality for fruits and vegetables subjected to various drying treatments. That is why it is important to build kinetic models to estimate the degradation rate of ascorbic acid during various drying processes. When the ascorbic acid content, total phenolic content, color, and rehydration properties of the final dried products were compared, it was seen that the hot air-microwave-assisted vacuum combination drying (HA-MVD) method yielded good quality dried product in quite shorter time as compared to other methods. The results of this study show that the HA-MVD method could be successfully applied for drying of kiwifruits.