Extraction of rosmarinic acid from Salvia officinalis L. using tunable deep eutectic solvent and its physiochemical properties

Abstract

Rosmarinic acid (RA) is a phenolic compound known for its remarkable antioxidant, antiallergic, antimicrobial, anticarcinogenic and anti-inflammatory properties, making it highly valuable for diverse industrial applications such as medicine formulation, cosmetic production and food additives. This study focused on the green extraction of RA and antioxidants from Salvia officinalis L. using deep eutectic solvents (DESs). Various DESs were prepared using choline chloride (ChCl) as the sole hydrogen bond acceptor (HBA) with various hydrogen bond donors (HBDs), including acetic acid (AA), propanoic acid (PA), malonic acid (MA) and ethylene glycol (EG) at different compositions (1:1, 1:2 and 2:1) and water content (0–30%). The resulting clear and homogeneous DESs were characterised by Fourier-transform infrared (FTIR) analysis, density measurements and Nile red assay to investigate their physicochemical properties. Ultrasound-assisted extraction was performed with the successfully formed DESs at 70°C for 30 min, using a solid-solvent ratio of 1:30 g/mL to extract RA and antioxidants from S. officinalis L. leaves. Stable DESs (ChCl-AA, ChCl-MA, ChCl-PA and ChCl-PG) were formed at the molar ratio of 1:2. The formation of hydrogen bonds in the DESs was confirmed by FTIR spectra (3800–3000 cm−1). The DESs densities decreased with increasing temperature and water content. ChCl-MA DES was the most polar, with the lowest transition energy, (Formula presented.) value of 44.672 kcal mol−1. ChCl-EG DES extract (1:2 molar ratio, 30% water content) yielded the highest RA (49.619 ppm), which is 12.2% higher than the methanol extract. ChCl-MA DES extract (1:2 molar ratio, 10% water content) showed 11.57% higher antioxidant activity than methanol extract, with an inhibition percentage of 92.663%. Overall, ChCl-EG (30% water content) and ChCl-MA (10% water content) at the molar ratio of 1:2 are viable green alternatives to conventional solvents for extracting RA and antioxidants from S. officinalis L., respectively.