Optimized Ultrasonic-Assisted Deep Eutectic Solvent Extraction of Polyphenols from Pleurotus eryngii: Enhanced Yield, Stability, and Antioxidant Activity

The extraction of bioactive polyphenols from Pleurotus eryngii (PEPs) offers promising applications in nutraceuticals and functional foods. However, conventional extraction methods are often inefficient and environmentally taxing. This study aimed to develop an optimized ultrasonic-assisted deep eutectic solvent (UDES) extraction process to enhance the yield, stability, and antioxidant activity of PEPs using a green and sustainable approach.

Twelve deep eutectic solvents (DESs) containing 10–20% water were synthesized and screened for their polyphenol extraction efficiency. Among them, choline chloride–ethylene glycol (ChCl–EG, 1:2) demonstrated the highest extraction capacity. The DESs' physicochemical properties, including their viscosity, density, and pH, were characterized at different temperatures. FTIR confirmed the presence of hydrogen bond interactions and successful DES formation. Process optimization was performed using single-factor experiments followed by the application of the response surface methodology (RSM). The optimal extraction conditions were identified to be 50 °C, 320 W ultrasonic power, a solid-to-solvent ratio of 60 g/L, and a 20 min extraction time, yielding 39.31 ± 1.3 mg gallic acid equivalents (GAE)/g, closely matching the RSM-predicted value of 39.40 mg GAE/g.

FTIR and SEM analyses confirmed that UDES synergistically enhanced the stability of the extracted PEPs, while HPLC identified gallic acid (9.14 mg/g) as the main phenolic compound. Antioxidant activities assessed through ABTS, DPPH, and FRAP assays showed significant improvements with UDES extraction, reaching 100% inhibition or activity in all tests. For ABTS, the values increased from 12.5 ± 1.90% (WC) to 15.04 ± 1.61% (UWC), 39.68 ± 1.71% (EC) to 49.70 ± 0.54% (UEC), and 63.74 ± 0.44% (DES) to 100% (UDES extraction), with ultrasonication enhancements of 20.25%, 25.25%, and 56.88%, respectively. Similarly, DPPH scavenging rose from 25.22 ± 1.13% (WC) to 28.81 ± 2.52% (UWC), 46.69 ± 2.26% (EC) to 56.41 ± 0.67% (UEC), and 70.76 ± 1.75% (DES) to 100% (UDES extraction), reflecting increases of 14.23%, 20.82%, and 41.30%, respectively. For FRAP, the values improved from 25.59 ± 1.56 (WC) to 30.20 ± 1.87 (UWC), 45.04 ± 0.84 (EC) to 56.66 ± 1.40 (UEC), and 72.69 ± 7.87 (DES) to 100% (UDES extraction), with respective ultrasonication enhancements of 17.99%, 25.69%, and 37.56%.

In conclusion, UDES extraction is a highly efficient and eco-friendly technique for extracting polyphenols from P. eryngii, offering significant potential for the valorization of mushroom by-products in health-related applications.