Investigation of drying kinetics and physicochemical properties of mulberry leather (pestil) dried with different methods

Abstract

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.