Optimization of Sequential Microwave–Ultrasound-Assisted Extraction of Turmeric (Curcuma longa L.) Using Response Surface Methodology and Evaluation of Its Antioxidant Activity

Abstract

Turmeric (Curcuma longa L.) is a natural source of curcuminoids, particularly curcumin, with potential applications in food, pharmaceutical, and cosmetic products. This study evaluated a two-stage microwave pretreatment-ultrasound- assisted extraction process for curcumin recovery from turmeric. Separate three-factor Box–Behnken designs were used to evaluate the effects of liquid-to-solid ratio (LSR), microwave power, and extraction time during microwave-assisted extraction (MAE), and the effects of LSR, extraction temperature, and sonication time during ultrasound-assisted extraction (UAE). Curcumin concentration was determined using UV–Vis spectrophotometry at 465 nm. The MAE model was significant (p < 0.0001) and showed that LSR was the most influential factor. The highest observed MAE yield was 6.354 mg g⁻¹ at an LSR of 5:1 mL g⁻¹, microwave power of 500 W, and extraction time of 1.5 min. The UAE model was also significant (p = 0.0089), with LSR and temperature significantly affecting curcumin yield. The highest observed UAE yield was 10.783 mg g⁻¹ at an LSR of 30:1 mL g⁻¹, 40 °C, and 5 min. The highest- yield extract exhibited an IC₅₀ value of 6.22 mg L⁻¹ in the DPPH assay. These results indicate that the two-stage extraction approach can improve curcumin recovery; however, independent validation experiments are required to confirm the predicted optimum conditions.