Optimization of the Extraction of Total Flavonoids and Antioxidant Activity from Lippia multiflora Moldenke (Verbenaceae) Leaves using Experimental Design

The leaves of Lippia multiflora contain secondary metabolites including flavonoids which have an important antioxidant activity. This study aims to optimize the extraction conditions of total flavonoids and the antioxidant activity of these leaves. To achieve this, the Plackett-Burman design was used for the screening of the factors influencing the extraction, then the central composite design was implemented for the optimization itself. The effects of five factors, such as the plant-to-solvent ratio, the nature of the extraction solvent, the extraction time, the extraction method and the size of the L. multiflora leaves, on the extraction of total flavonoids and the antioxidant activity were studied. Results of Plackett-Burman design indicated that factors influencing both flavonoids extraction and antioxidant activity were the solid-liquid ratio and extraction time. The predicted optimal conditions for the highest flavonoids content from L. multiflora leaf with better antioxidant activity were found with aqueous decoction for 30 min with 3.5 g of cut leaves in 100 mL of distilled water. Using the predicted conditions, experimental responses were 87.18 ± 1.03 mg/g QE and 372.34 ± 4.04 µmol/g TE for total flavonoids and antioxidant capacity, respectively. Under the above-mentioned conditions, the experimental results are very close to predicted one. Thus, L. multiflora leaf can be considered as a natural source of flavonoids content with good antioxidant activity.