PHENOLIC COMPOSITION AND ANTIOXIDANT ACTIVITY OF GREEN-SOLVENTS-BASED EXTRACTS OF RED ONION WASTES

Abstract

Onion represents one of the most important crop, based on its production,consumption and high pharmacological potential supported by its chemicalcomposition. Phytochemicals of phenolic structure, in particular anthocyanins, areamong the strongest antioxidant compounds with large biological and industrialapplications. Because their conventional extraction involves the use of highamounts of polar organic solvents, there is a strong requirement for development ofnew strategies based on greener solvents. The aim of the present paper was toextract valuable compounds of polyphenolic structure from red onion wastes usingdeep eutectic solvents, as green strategy for their isolation. In addition, the totalantioxidant activity as measured by ferric reducing antioxidant capacity assay wasinvestigated. Extraction performed at 40oC in the selected solvent system wasoptimized for two parameters, solvent/sample ratio and extraction time. Theobtained results showed the highest content of anthocyanins and antioxidantactivity at a solvent/sample ratio of 30/1 and the extraction time of 90 min, at 40oC.Regarding the total phenolics and flavonoids, the optimal extraction parameterswere 20/1 solvent/sample ratio and 90 min, at 40oC. Compared to conventionalextraction in organic solvent, the values of the antioxidant activity were similar,while those of the content of bioactive compounds were higher in extracts obtainedin ethanol solution. By further optimization of the extraction process, the obtainedproducts may find useful application in obtaining natural ingredients intended fordifferent purposes.