Oven, Temperature‐Controlled Microwave, and Shade Drying Effects on Drying Kinetics, Bioactive Compounds and Antioxidant Activity of Knotweed (Polygonum cognatum Meissn.)

Abstract

AbstractIn this study, the plant node was dried in an oven (40, 50 and 60 °C), shade and temperature‐controlled microwave (40, 50 and 60 °C) methods. Statistically (p<0.05), the values closest to the color values of fresh grass were determined in an oven at 40 °C drying temperature. Effective diffusion values varied between 8.85×10−8–5.65×10−6 m2 s−1. While the activation energy was 61.28 kJ mol−1 in the oven, it was calculated as 85.24 kJ mol−1 in the temperature‐controlled microwave. Drying data was best estimated in the Midilli‐Küçük (R2 0.9998) model oven at 50 °C. The highest SMER value was calculated as 0.0098 kg kWh−1 in the temperature‐controlled microwave drying method. The lowest SEC value in the temperature‐controlled microwave was determined as 24.03 kWh kg−1. It was determined that enthalpy values varied between −2484.66/−2623.38 kJ mol−1, entropy values between −162.04/−122.65 J mol−1 and Gibbs free energy values between 453335.22–362581.40 kJ mol−1. Drying rate values were calculated in the range of 0.0127–0.9820 g moisture g dry matter−1 in the temperature‐controlled microwave, 0.0003–0.0762 g dry matter−1 in the oven, and 0.001–0.0058 g moisture g dry moisture matter−1 in the shade. Phenolic content 6957.79 μg GAE g−1 fw ‐ 48322.27 μg GAE g−1 dw, flavonoid content 3806.67 mg KE L−1 fw ‐ 22200.00 mg KE L−1 dw and antioxidant capacity 43.35 μmol TE g−1 fw ‐ 323.47 μmol TE g−1 dw. The highest chlorophyll values were obtained from samples dried in an oven at 40 °C. According to the findings, it is recommended to dry the knotweed (Polygonum cognatum Meissn.) plant in a temperature‐controlled microwave oven at low temperatures. In this study, in terms of drying kinetics and energy parameters, a temperature‐controlled microwave dryer of 60 °C is recommended, while in terms of quality characteristics, oven 40 °C and shade methods are recommended.