Determination of some quality parameters and ascorbic acid and color change degradation kinetics in kiwifruit dried by different drying methods

In this study, it was aimed to determine the ascorbic acid and color change kinetics during drying of kiwifruit using different drying techniques. In addition, the rehydration capabilities of the dried products were determined at two different temperatures (20 and 50 °C) and three different models (Peleg, Weibull and first-order kinetic model) that are widely used in the literature were examined to explain rehydration behaviors. For this purpose, kiwi fruit cut in slices was dried by using conventional hot air drying (60 °C), vacuum drying (60 °C), freeze drying and hot air pre-drying (60 °C) microwave assisted vacuum drying combination (450 W) methods.The ascorbic acid content of the kiwi fruit before drying was determined as 249.17 mg / 100g dry matter. Ascorbic acid content was found to decrease by 77.52%, 75.41%, 39.86% and 29.64% by hot air drying, vacuum drying, MVK drying and freeze drying, respectively. Three different models (zero and first order kinetic model, Weibull model) were examined to fit data of ascorbic acid content change with time. For all drying processes, it was determined that the model that best describes the change in the amount of ascorbic acid over time is the Weibull model. When looking at the color values, the lightness (L *) values of the products dried by hot air, MVK and vacuum drying methods were similar to those of the fresh sample, while the values of the lyophilized samples were higher than the fresh sample. The a * values of the samples increased in all drying methods except freeze drying method. Freeze-dried samples have the lowest a * values. The b * values of the samples in all drying methods increased significantly in the initial times of drying. Three different models (zero and first order kinetic model, combination model) were examined to fit data of L*, a* and b* values versus drying time. It is seen that only the a * color values of all samples except for the kiwi sample dried with the lyophilizer fit zero -order kinetics. It was determined that L * values of kiwi slices dried by freeze drying and MVK method followed the combined kinetic model. It was determined that the change in b * values also fit this model for all drying processes, while the change in a * values fit this model except for the lyophilized sample. It has been determined that the drying method and the rehydration temperature are effective on the rehydration rate of dried kiwifruit slices. For all drying methods, experimental rehydration data obtained at both temperatures were found to fit the Weibull model. SEM images of the dried products were also obtained in this study.