Response surface modeling and optimization of the extraction conditions using lactic acid-based deep eutectic...

Most recurrently available organic solvents are toxic and inflammable and pose high risks to human health. Natural deep eutectic solvents (NADESs) have been developed as promising green alternatives.

We aimed to extract polyphenolic compounds from Mentha pulegium using lactic acid-based deep eutectic solvents. Extraction parameters were optimized by response surface methodology.

Combined with ultrasound-assisted extraction, three different lactic acid-based deep eutectic solvents were investigated for the extraction of polyphenols. Methanol (80%, v/v) was used for comparison. The optimized influencing factors were: water content in solvent, extraction time, and temperature. The design was adopted including 17 experiments with three center points.

All NADESs tested showed an excellent extraction efficacy compared to 80% methanol. Under the optimized conditions, with 45% of water, at 30°C, and for extraction 90 min, the highest extraction yields were recorded using lactic acid:sodium acetate (3:1), achieving 173.35 ± 0.02 mg gallic acid equivalents (GAE)/g dry weight (dw) of polyphenols and 95 ± 0.09% antioxidant activity. After extraction for 90 min at 80°C with 18% of water, we obtained 164.06 ± 0.01 mg GAE/g dw and 94 ± 0.02% antioxidant activity using lactic acid:glucose (5:1). Efficient recovery (64.92 ± 0.01 mg GAE/g dw and 97 ± 0.1% antioxidant activity) was achieved using lactic acid:glycine (3:1) with 31% of water, at 35°C, and extraction for 30 min.

Our results indicate that with optimized parameters, the proposed natural solvents are excellent alternatives to chemical ones for the extraction of phenolic compounds.