Improvement of intermittent microwave drying of red peppers: Effect of ethanol and blanching pretreatments on drying behavior, modeling, energy consumption and some quality attributes

This research explores the potential of intermittent microwave drying as an alternative to sun and hot air drying. It also evaluates ethanol immersion (a new pretreatment method), along with traditional hot water and steam blanching pretreatments, to enhance drying efficiency. Key aspects studied include drying characteristics, moisture diffusion, thermal properties, energy consumption, modeling techniques, color changes, and shrinkage in red peppers. The drying was performed at 80, 240, and 400 W, with pretreated samples dried at 240 W. The shortest drying time was 27.5 min at 400 W and 40 min with 100 % ethanol at 240 W (240 W-100ET10) for pretreatments. The highest effective moisture diffusivities (D_eff) and mass transfer coefficients (h_m) for unpretreated samples were at 400 W. Among pretreatments, 240 W-100ET10 had the highest D_eff and h_m. Artificial neural network modeling outperformed thin layer modeling with higher R² and lower RMSE. Thermal properties, including specific heat and thermal conductivity, decreased during drying. The highest specific moisture evaporation rate and lowest specific energy consumption were 0.244 kg kWh⁻¹ and 4.105 kWh kg water^-1, respectively, for 240 W-100ET10. L* values decreased during drying, with notable changes in a* and b* values. Besides, thickness shrinkage decreased by higher microwave power and pretreatments. According to principal component analysis, hot and steam blanching and 400 W, %50 ethanol immersion for 10 min and 240 W, 80 W and 240 W-100ET10 showed similarities. Ethanol pretreatment and higher microwave power may be considered as promising methods for optimization of intermittent microwave drying of red peppers.