Sliced kumquats were dried by using three different drying methods, microwave (375 W), hot air (70 and 80 °C), and vacuum (70 and 80 °C with 100 and 300 mbar) to determine drying characteristics, antioxidant capacity and total phenolic content and color. All color parameters (L, a, b, C ab , ΔE and h°) changed depending on the drying methods. Page and Modified Page models are the best fitted drying methods with the highest value of R 2 (0.9994) and the lowest values of RMSE (0.000635-0.000735) and χ 2 (0.000010-0.000013) compared to other models. Effective moisture diffusivity values for dried kumquats ranged from 1.54 × 10-8 to 8.24 × 10-8 in vacuum drying at 70 °C-300 mbar and microwave drying at 375 W, respectively. On comparison to the fresh sample, the dried samples showed an increase in both total phenolic content and antioxidant capacity. The total phenolic content (3095.71 ± 101.41 mg GA/100g d.w) and antioxidant activity (10.51 ± 0.19 µmol TE/g d.w) with DPPH assay showed the highest levels for the vacuum drying at 70 °C-100 mbar method. Microwave dried samples had the highest antioxidant activity with CUPRAC assay as (17.58 ± 0.63 µmol TE/g d.w.). This study indicated that microwave drying and vacuum drying at 70 °C-100 mbar were able to yield high-quality kumquat slices.

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Microwave pre‐treatment for vacuum drying is a promising method in order to enhance heat and mass transfer rate. In this study, the influences of microwave pre‐treatment (90 W 30 min) on vacuum drying conducted at different combinations of drying temperature and absolute pressure (60, 70, and 80°C with 15 and 30 kPa) were investigated by evaluating the drying characteristics, rehydration capacity, and some quality attributes of orange slices. The vacuum drying treatments were carried out both with (MWVD) and without the microwave‐pretreatment (VD) at the same temperature and absolute pressure combinations. It was revealed that application of MWVD shortened the drying time of orange slices while increasing drying rate, effective moisture diffusivity and rehydration capacity. Six different semi‐theoretical mathematical models were applied, and Page, Modified Page, Logarithmic, and Lewis models were best fitted to experimental data of orange slices. It was observed that, among the different drying conditions applied in the scope of the study, VD at 80°C–15 kPa caused lowest color change (ΔE) that indicates the difference between the dried and fresh orange slices. All drying treatments caused a reduction in ascorbic acid content (AAC) (56.24–59.34%), total phenolic content (TPC) (15.92–55.79%) and total antioxidant capacity (TAC) (6.05–35.18%, 21.03–42.28%, and 54.76–69.07% for DPPH, FRAP, and CUPRAC assays, respectively) of orange slices. When MWVD and VD were compared, it was observed that MWVD caused less decrease in TPC and more in AAC and TAC. In conclusion, MWVD method is suggested as the more effective method providing lower drying time, faster drying rate, and better quality parameters of the product. Practical applications Orange including various nutrients with health beneficial effects is a perishable fruit. Therefore it is processed in to frozen, dried, canned, jam and fruit juice forms in order to increase its shelf life. Especially in seasons with overproduction, orange can be processed into dried form, and it can be turned into an alternative healthy snack with increased commercial value. In this research, drying characteristics of orange slices by microwave pre‐treated for vacuum drying were assessed with mathematical modeling. Drying conditions affected rehydration capacity, total phenolic content (TPC), total antioxidant capacity (TAC), ascorbic acid content (AAC) and color values of orange slices. Based on those outcomes, the optimum process conditions for an industrial drying application can be designed to enhance heat and mass transfer rate and to improve quality attributes of the product.

The effects of microwave (90 and 180 W), hot air (60 and 70°C) and vacuum (60 and 70°C with 250 mbar) drying techniques on drying characteristics, total phenolic content (TPC), antioxidant capacity (AC), color and texture of mulberry pestils were investigated. L*, b*, C*, and h° decreased while a* value was generally increased in pestils. Hardness, springiness, chewiness, and gumminess of the samples were found to be significantly different (p < 0.05). Between the applied seven thin layer drying models, Page and Modified Page were best fitted with the highest R2 (0.9997) and the lowest values of RMSE (0.000927) and χ2 (0.000011). Effective moisture diffusivity (Deff) of pestils ranged from 4.42 × 10−8 to 8.47 × 10−7 m2/s. Drying treatments caused an increment in TPC (1.41%–57.13%) and AC (0.37%–72.79%). These highest results were both obtained from microwave 180 W (TPC: 209.14 mg GAE/100 g dw and AC: 181.37 μmol TE/100 g dw). Practical applications Mulberry is a perishable fruit with several health benefits. It can be consumed raw or in the form of fruit leather (pestil), jam, jelly, marmalade. By pestil production, in which fruit pulp is dehydrated into leathery sheets, mulberry can be processed into a nonseasonal shelf life prolonged product for markets without the additon of preservatives. In this study, drying kinetics of mulberry pestil by microwave, hot air, and vacuum methods were evaluated via mathematical modeling. Page and Modified Page were the best thin layer drying models for pestil production. Drying characteristics were assessed for the development of food specific system in industrial usage and the simulation and optimization of the drying process. Drying treatmens affected texture and color of pestils significantly while exerting higher total phenolic content and antioxidant capacity when compared to non‐dried formulation. Microwave was determined as a promising method to yield high‐quality pestils with greater nutritional properties and the advantage of reduced drying times.

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