Onion husk (Állium cépa) as a promising source of natural antioxidants

Abstract

The search for new sources of natural antioxidants is an important area of research. The total antioxidant capacities (TAC) of ethanol and aqueous extracts of yellow, red and white onion husks, rosemary and basil were determined by the Oxygen Radical Absorbance Capacity method using fluorometer Fluoroskan Ascent FL and the Ferric Reducing/Antioxidant Power spectrophotometer SF-2000 and expressed in µmol-equiv. Trolox/g of a sample and µmol-equiv. dihydroquercetin / g of a sample, respectively. Ethanol and aqueous extracts of red onion husk demonstrated the greatest TACs and amounted to 709.17±21.68 µmol-equiv. Trolox/g and 2048.83±64.97 µmol-equiv. Trolox/g, and these significantly exceeded the TACs of such popular spices in the food industry as basil and rosemary. TACs of both extracts of yellow onion husk were approximately equivalent to rosemary. Ethanol extracts of red and yellow onion husk demonstrated the greatest TACs and amounted to 2005.64±33.59 µmol-equiv. dihydroquercetin /g and 941.39±65.43 µmol-equiv. dihydroquercetin /g, respectively, and these significantly exceeded the corresponding TACs of basil and rosemary. TACs of aqueous extracts were approximately equivalent to rosemary, but below the TAC of basil. The absence of bright taste and aroma of red and yellow onion husk extracts, high total antioxidant capacity for neutralization of free radicals by both mechanisms of interaction, as well as the availability of raw materials in large scale confirms that this waste of the fruit and vegetable industry is a promising source of natural antioxidants.