Extraction of phenolic compounds and evaluation of the antioxidant and antimicrobial capacity of red onion skin (Allium cepa L.)

This study evaluated the content of phenolic compounds, total flavonoids and anthocyanins, as well as the antioxidant and antimicrobial activity, of red onion skin extract (Allium cepa L.) that was obtained by conventional extraction at different times (30, 60, 120 and 240 minutes) and using different concentrations of ethanol (20, 40, 60 and 80%). The antioxidant activity of the extracts was evaluated using the following methods: DPPH radical sequestration, the inhibition of the auto-oxidation of the ?-carotene system, FRAP and IC50. The antimicrobial activity was evaluated by the disk diffusion method. The best results for phenolics, flavonoids and anthocyanins were found using extraction with 80% solvent at 165, 60 and 120 minutes respectively. In relation to the antioxidant activity using the FRAP, DPPH and IC50 methods, the best values were found using 80% solvent at 120, 30 and 30 minutes of extraction respectively. The best value for antioxidant activity determined by the ?-carotene method was with 59.32% solvent at 240 minutes of extraction. No antimicrobial activity of the extracts in relation to the tested microorganisms was detected. The results of this study showed that the concentration of 80% ethanol favored the extraction of phenolic compounds, flavonoids and total anthocyanins, as well as producing the highest antioxidant activities found by the different methods. The best extracts in terms of antioxidant activity by the DPPH and IC50 methods were obtained with the lowest extraction time of 30 minutes, in contrast to the extraction time of 240 minutes, which produced the highest antioxidant activity by the ?-carotene methods