Effect of maceration time and type of solvent on the content of phenolic compounds and antioxidant activity of Digitalis purpurea L

The extraction of chemical compounds from plants is influenced by various factors, such as methodology and duration of extraction, sample preparation, and the type and concentration of solvent used. This study was performed to investigate the effect of extraction time and type of solvent on the contents of phenolic compounds, flavonoids, and antioxidant activity of Digitalis purpurea L. plant.

An experiment based on a completely randomized design in a factorial arrangement with three replications was conducted at the Horticulture Laboratory at the University of Zanjan, Zanjan, Iran, in 2021. The experimental treatments included two levels of extraction duration (24 and 48 h) as the main factor, and two levels of methanol, ethanol, and acetone solvents (100% and 80%), compared with the control (distilled water), as sub-factors. Extraction of purple foxglove leaf powder was done by macerating 24 or 48 h using two levels of methanol, ethanol, or acetone as solvents (100%, 80%, and distilled water for the control). Evaluation of phenolic compounds, flavonoids, and antioxidant activity was performed. The resulting data were analyzed in SAS software version 9, and mean comparisons were performed by Duncan's Multi-Range Tests at the 1% and 5% probability levels. To determine the correlation between parameters, Pearson's correlation coefficient was checked using SPSS version 20 software.

The results showed that there was a significant difference between 24 and 48 h of maceration to extract chemical compounds (P<0.01). The highest amounts of total phenol (24.75 mg GAE/g dw) and antioxidant activity (71.36%) were obtained in 80% acetone extract, and the maximum flavonoid content (6.03 mg Q/g dw) was achieved in 80% ethanol and 48 h maceration time. Generally, increasing the maceration time from 24 h to 48 h caused a significant rise in the extraction of phenolic compounds, flavonoids, and antioxidant activity. Moreover, there was a positive correlation between flavonoid content (P=0.86) and phenolic content (P=0.82) with antioxidant activity.

According to the results, increasing the extraction time and also utilizing hydroalcoholic solvents were more effective in extracting these compounds than pure alcohols.