Modeling Thin-Layer Drying Kinetics of Justicia adhatoda Leaves Using Different Drying Techniques and Its Quality Evaluation

Abstract

Drying of medicinal herbs like Justicia adhatoda is essential to maintaining their bioactive constituents, but conventional methods tend to degrade quality by subjecting them to excessive heat for long periods. To overcome this, the current research compares and assesses the drying kinetics, phytochemical retention, and optical quality of J. adhatoda leaves under cabinet tray drying (CTD) and microwave drying (MD). Since the plant has pharmacological importance, the research seeks to select a drying process that guarantees efficiency and quality retention. Experimental drying was carried out at different temperatures (45°C–75°C) for CTD and microwave powers (200–700 W) for MD. Among the 11 thin-layer models, Page's model proved to be the most reliable in predicting drying behavior for both processes (R² = 0.999) for CTD and (R² = 0.996) for MD. MD under 360 W took the shortest time, whereas 200 W maintained the maximum total flavonoids and tannin contents. Antioxidant activity was maximum at 360 W, indicating maximum retention of functional constituents under optimal microwave power. Microwave-dried samples exhibited better color preservation, demonstrating its capability to retain sensory as well as commercial acceptability. The results of this study have important consequences for the herbal processing industries, allowing scalable, high-quality drying schemes to be developed that protect the therapeutic and cosmetic worth of medicinal crops.