Optimization of ultrasonic and microwave-assisted extraction with natural deep eutectic solvents for enhanced recovery of phenolics and terpenoids from celery leaves

Abstract

Celery (Apium graveolens L.) is a widely available plant rich in bioactive compounds, known for its therapeutic properties. This study aims to determine the optimal conditions for the extraction of phenolics and terpenoids from celery leaves. Various natural deep-eutectic solvents were screened under fixed conditions of ultrasonic-assisted extraction (UAE) and microwave-assisted extraction (MAE), and the most suitable solvent for extraction was the solvent composed of acetic acid and glucose. Single-factor experiments were run to assess the influences of various independent variables, including the ratio of sample to solvent, the water content of the solvent, ultrasonic power, ultrasonic time, ultrasonic temperature, microwave power, and microwave time, on the phenolics and terpenoids extraction efficiency. Optimization of extraction conditions was conducted using the Box–Behnken design model. For the MAE method, the optimal conditions for phenolics and terpenoid recovery were a sample-to-solvent ratio of 0.019 g/mL, 10.0% water content, 86.043 W of microwave power, and 4.0 min of microwave time. Under these conditions, the total phenolic content was 36.06 ± 2.88 mg gallic acid equivalent (GAE)/g, and the total terpenoid content was 56.22 ± 1.01 mg ursolic acid equivalent (UE)/g. For the UAE method, the optimal conditions for phenolics recovery were a sample-to-solvent ratio of 0.019 g/mL, 20.66% water content, 54.14 ℃ temperature, 18.71 min of extraction time, and 336.51 W ultrasonic power. For terpenoids, the optimal UAE conditions were a sample-to-solvent ratio of 0.018 g/mL, 10.60% water content, 37.28 ℃ temperature, 18.71 min of extraction time, and 416.22 W of ultrasonic power. These conditions yielded 37.7 ± 1.95 mg GAE/g of total phenolic content and 76.22 ± 0.712 mg UE/g of total terpenoid content. The results imply the efficiency of the solvents and the extracting methods, suggesting their potential in the recovery of terpenoid and phenolic compounds from celery leaves.