Determination of drying characteristics of pumpkin and sweet potato dried with hot air-microwave combination and optimization by response surface methodology

In this thesis study, the effects of hot air, microwave and hybrid (hot air-microwave) drying methods on pumpkin and sweet potato samples were investigated. Drying characteristics and quality parameters such as drying rate, moisture content change, effective moisture diffusivity, energy consumption, rehydration rate, water holding capacity, color change, antioxidant activity, total phenolic content, beta carotene content of the samples dried under 15 different drying conditions including solo and combination of three different drying temperatures (50, 60 and 70 °C) and microwave power levels (90, 180 and 360 W) were investigated, and modeling for drying kinetics and optimization studies were carried out with response surface method for drying process. The best models explaining the drying kinetics of pumpkin and sweet potato samples were; Alibas, Midilli-Küçük and Weibull model. While the rehydration ratio increased for both samples with increasing microwave powers, the rehydration ratio of pumpkin decreased with imcreasing drying temperature, while the rehydration capacity of sweet potato remained unchanged. In solo drying methods, water holding capacity decreases as microwave power increases, while it increases with increasing drying temperature. For pumpkin and sweet potato samples, antioxidant activity values increased under all drying methods and conditions, while total phenolic content and beta carotene content decreased. The optimum drying temperature and microwave power for the hybrid drying process of pumpkin and sweet potato were determined as 56.55 °C-148.52 W and 62.43 °C-53.48 W, respectively.