Ultrasound-Assisted Extraction, Macroporous Resin Purification, and Antioxidant Activity of Chlorogenic Acid from Eucommia ulmoides Leaves

Chlorogenic acid from <i>Eucommia ulmoides</i> leaves is a promising natural antioxidant for food applications, yet its extraction and purification require optimization to improve yield and purity. This study employed ultrasound-assisted ethanol extraction on fresh leaves, evaluating the effects of ethanol concentration, solid-to-liquid ratio, extraction time, and temperature on CGA yield. Optimal extraction parameters were determined using response surface methodology. Purification with NKA-II macroporous resin increased CGA purity to 82.72%. SEM analysis revealed wrinkled and porous surface structures, while FTIR confirmed the presence of characteristic hydroxyl, carbonyl, and aromatic groups. Under optimized conditions (70% ethanol, solid-to-liquid ratio 1:20 g/mL, 58 °C, 61 min), the extraction yield reached 6.96%. In vitro assays demonstrated strong antioxidant activity, with scavenging rates of 96.01% for DPPH, 89.69% for hydroxyl, and 99.82% for ABTS radicals at 5 mg/mL. These findings provide an efficient method for obtaining chlorogenic acid from <i>Eucommia ulmoides</i> leaves and support its potential as a functional food ingredient.