Ultrasound-assisted extraction of anthocyanins from red onion skin, and determination antioxidant activities in red onion

Anthocyanins, a class of polyphenols, are the pigments responsible for the red, purple and blue colors of mostfruits and vegetables. Interest in using anthocyanins as value added natural alternatives to the use of synthetic foodcolorings has increased in recent years, especially with the recognition of potential adverse health effects from theconsumption of synthetic colorings[2]. It is known that anthocyanin pigments act as strong antioxidants and are antiinflammatory,with antimutagenic and cancer chemopreventive activities [1]. Several technologies for the extractionof anthocyanin pigments from various plants sources have been proposed in literature [1]. conventional solventextraction techniques have some limitations. These include mass transfer resistances, the large amount of solventused in classical extraction methods, long extraction time, high extraction temperature, health related risks and lowefficiency and extraction yield[3,4]. Ultrasound-assisted extraction can be used as a tool to overcome the drawbacksof conventional solvent extraction methods and to improve some benefits of the solvent extraction process [5]. In thisstudy, Ultrasound-assisted extraction of anthocyanin compounds was optimized, Among the experimental rangeused for testing the variables, extraction with 80% solvent concentration, 50 mL/g liquid solid ratio, 65⁰C extractiontemperature and 11.5 min extraction time resulted in the highest level of TAC (13.22 mg C3G/ g DW). The totalanthocyanins content in onion was utilized by the pH differential method. Anthocyanin content of freeze dried onionsample was 13.22 (mg anthocyanidin-3-glucoside/100 g dried onion). The total flavonols content in red onion skinwas measured by spectrophotometric method. The total polyphenol contents were also measured by means of Folin-Ciocalteu method. Moreover, all the concentrations of anthocyanins, flavonoids and polyphenols showedsignificantly positive correlations with antioxidant activities measured by DPPH, and FRAP assays.

Keywords:

Anthocyanins , Ultrasound , Antioxidant Activities