Optimization of ultrasonic-assisted osmotic dehydration as a pretreatment for microwave drying of beetroot (Beta vulgaris).

This article focuses on optimizing drying conditions for red beetroot (Beta vulgaris) using ultrasonic-assisted osmotic dehydration followed by microwave drying, employing the Box-Behnken design and response surface methodology (RSM). The study varied ultrasonic power, sonication time, salt concentration, and microwave power to maximize antioxidant capacity (measured by DPPH• % inhibition), total phenolic content (TPC), and desirable color attributes (L*, a*, b* values). Results identified optimal conditions at 5.15% salt concentration, 20 minutes sonication, 50 W ultrasonic power, and 716.45 W microwave power, which preserved bioactive compounds and improved color quality. Drying kinetics fitted well to the Midilli et al. thin-layer drying model (R² > 0.90), and effective moisture diffusion coefficients increased with higher microwave power and ultrasonic pretreatment. The study concludes that ultrasonic-assisted osmotic dehydration prior to microwave drying effectively maintains the quality characteristics of dried beetroot.