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 chemical
composition. Phytochemicals of phenolic structure, in particular anthocyanins, are
among the strongest antioxidant compounds with large biological and industrial
applications. Because their conventional extraction involves the use of high
amounts of polar organic solvents, there is a strong requirement for development of
new strategies based on greener solvents. The aim of the present paper was to
extract valuable compounds of polyphenolic structure from red onion wastes using
deep eutectic solvents, as green strategy for their isolation. In addition, the total
antioxidant activity as measured by ferric reducing antioxidant capacity assay was
investigated. Extraction performed at 40oC in the selected solvent system was
optimized for two parameters, solvent/sample ratio and extraction time. The
obtained results showed the highest content of anthocyanins and antioxidant
activity 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 parameters
were 20/1 solvent/sample ratio and 90 min, at 40oC. Compared to conventional
extraction in organic solvent, the values of the antioxidant activity were similar,
while those of the content of bioactive compounds were higher in extracts obtained
in ethanol solution. By further optimization of the extraction process, the obtained
products may find useful application in obtaining natural ingredients intended for
different purposes.