The effect of natural, convective, microwave and combined microwave-convective drying methods on the bioactivity of persimmon

Persimmon slices (Diospyros kaki L. cv. Fuyu), whose mass was 100 g and initial moisture content was 83,97 ± 0,01%, were dried by natural, convective, microwave, and combined microwave – convective drying methods until the final moisture content was 11,03 ± 0,01%. While the longest drying time was measured at natural drying with 6 510 minutes, the shortest drying time was obtained at 5 W g-1 – 130°C with 14 minutes. Drying data are modeled with 21 different thin-layer drying equations, and the most successful models were Logistic for natural drying, Alibas model for 70°C, 130°C, 4 W g-1 – 70°C, 4 W g-1 – 100°C, and 4 W g-1 – 130°C, Weibull distribution for 100°C, Jena and Das model for 3 W g-1, Verma et al. model for 3 W g-1 – 70°C and Page model for 5 W g-1 – 130°C. The most suitable model for all other drying methods was the Modified Henderson and Pabis model. In all of the thermal properties, the highest values were reached in the natural drying method. The best results were achieved at 3 W g-1 – 70°C for brightness, 5 W g-1 – 70°C for redness, yellowness, Chroma, total color change, and whitening index, natural drying for hue angle, and 5 W g-1 – 130°C for browning index. The protein and macronutrient elements closest to the fresh product were measured at 5 W g-1 and 5 W g-1 – 70°C. While the highest value for sodium is measured at 5 W g-1, iron and manganese were best preserved at 5 W g-1 – 70°C, copper at 4 W g-1 – 70°C, and zinc in the natural drying method. The highest percentage bioavailability for the total phenolic content was determined at 5 W g-1. In terms of antioxidant capacity, the highest percent bioavailability was obtained at 130°C in the DPPH and ABTS method and at 5 W g-1 – 100°C in the CUPRAC method. In addition, the DPPH method was determined as the most appropriate antioxidant capacity method in the study since it gave the highest results. The drying method in which the anthocyanin content was best preserved was 4 W g-1, while the lowest results were achieved at 70°C. The closest lycopene content to the fresh product was found at 4 W g-1 – 70°C, while the highest beta carotene and vitamin E were found at 5 W g-1 – 70°C. The highest levels of vitamin C and pyridoxine were measured at 3 W g-1, while the thiamine, niacin, and folic acid closest to fresh were detected at 130°C and 100°C, respectively.