Drying Behaviour and Quality Retention in Avocado (Persea americana) Leaves: A Comparison of Hot Air and Microwave Drying

Avocado (Persea americana) leaves are an underutilised plant material with potential applications as herbal teas and functional ingredients due to their phenolic and antioxidant compounds. However, limited information exists on suitable drying conditions to preserve their quality. This study investigated the effect of oven temperatures (50, 60 and 70°C) and microwave power levels (200, 500 and 700W) on the drying behaviour and quality attributes of avocado leaves. Leaves were dried in a hot air oven and a digital microwave oven until equilibrium moisture content was reached. Initial moisture content and water activity of fresh leaves averaged 1.40 g Hâ‚‚O/g DM (58.34% wb) and 0.958, respectively. Increasing temperature and microwave power significantly reduced drying time, with microwave drying achieving comparable moisture reduction in substantially shorter times. Drying occurred predominantly in the falling rate period. Drying rate constants and effective diffusivity increased with both temperature and microwave power level, with higher values observed for microwave drying. Quality evaluation showed that microwave drying, particularly at 700W, resulted in significantly higher (p ≤ 0.05) retention of total phenolic content, antioxidant capacity, flavonoids and condensed tannins compared to oven drying. Selected thin-layer models adequately described drying behaviour under both methods. The results indicate that microwave drying at 700W is an efficient method for rapid drying of avocado leaves while preserving key bioactive compounds.