Drying kinetics of persimmon dried by microwave and hot air combination and quality characteristics of the powder product

In this study, persimmon (Diospyros kaki L.) fruit was previously separated from its fruit skin and seeds and pureed with the help of a blender, and then subjected to three different drying methods: hot air (SH), microwave (MD) and microwave-hot air combination (MDSH). 8 models: SH (50 °C and 75 °C), MD (100 and 200 W) and MDSH (100 W-50 °C, 100 W-75 °C, 200 W-50 °C, 200 W-75 °C). Different drying methods were applied, and the samples obtained showed moisture content, drying rate, energy consumption, bulk, tapped and particle density, porosity, flowability and cohesiveness values, swelling capacity, water retention capacity, rehydration, color values (L, a*, b*, C, a°, ΔE), total phenolic substance and antioxidant capacity were examined. The results showed that increasing drying air temperature and microwave power levels caused shorter drying time and the drying process took place in a decreasing period. Among the applied drying methods, the MDSH method provided significantly higher drying rate and greater moisture removal. Although the samples are similiar in terms of moisture content and drying speed, it was observed that the sample dried with hot air at 50 °C dried the slowest and had the highest moisture content because of drying, while 200 W-75 °C had the lowest moisture content in the shortest time. While significant changes were observed in the bulk and compressed density values of persimmon powder samples obtained with different drying methods, no statistical difference was observed in particle density (p<0.05). The lowest porosity values of persimmon powders are 37.99% at 200 W-75 °C; The highest value belongs to 50 °C and is 77.57%. The flowability and porosity values of the samples showed significant increases in the samples dried with the MDSH method. Total phenolic substance and antioxidant capacity were found to decrease with increasing temperature and MDHS methods. Compared to the raw material, the closest values in terms of total phenolic substance and antioxidant capacity of fresh persimmon were obtained in 50 °C hot air drying, while the lowest values were obtained in MDSH applications. When the color values were examined, a decrease in the L* value was observed for all drying conditions compared to the fresh sample, while an increase in the a* value was observed. In terms of ∆E value, it was determined that the lowest value belonged to the 100 W-75 °C MDSH method, while the highest value belonged to the 200 W-75 °C MDSH method. Considering all the results, it was recommended to combine MD and SH drying techniques to minimize the negative effects of SH only and/or MD only methods.