Optimization of the microwave assisted extraction and biological activities of polyphenols from lemon verbena leaves

Abstract

The present study aims to optimize the extraction of phenolics by microwave-assisted extraction (MAE) using the response surface methodology (RSM), from Lemon verbena leaves. The optimized extract was tested for its antioxidant activity using two methods (DPPH and reducing power) and its antibacterial efficiency by using disk diffusion assay and broth microdilution, against two Gram-negative (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853) and two Gram-positive (Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633) strains. Under the optimized conditions (40% (v/v): of ethanol concentration, 188 s of irradiation time, 600 W of microwave power and 1:40 g/mL of solid-to-liquid ratio) the total phenolic content (TPC) was 67.87±1.61 mg GAE/g DW. The IC₅₀ of the extract was 139.65±1.44 µg/mL and 56.60±2.79 µg/mL for DPPH inhibition and reducing power, respectively. The best antibacterial activity was shown by the extract obtained by MAE with lower MBC (1.56 to 18.75 mg/mL) and MBC/MIC ratio. Lemon verbena extract can be used as an ingredient in cosmetics, food supplements and herbal medicinal products due to its interesting biological properties.