An Investigation on the Recovery of Antioxidant Phenolics from Onion Solid Wastes Employing Water/Ethanol-Based Solvent Systems

Onion solid wastes, composed of the apical trimmings and the outer dry layers of the bulb, were used as raw material for the recovery of antioxidant phenolics by employing acidified water/ethanol-based solvent systems. The extraction efficiency was assessed by measuring the reducing power and the antiradical activity of the extracts, and the total polyphenol yield. Improvement of the extraction yield was based on modifying the solvent composition and the operating conditions (temperature, time). Initial screening of various mixtures showed that significantly higher recoveries (P < 0.001) can be attained by using 60% ethanol containing 0.1% HCl. The assessment of factors affecting yield, including extraction time and temperature, was accomplished using a series of extractions on the basis of a 2 x 3 factorial design model, with time and temperature values varying from 0.5 to 6 h and from 40 to 60A degrees C, respectively. The results obtained showed that improvement of yield is dependent upon increasing extraction time up to 6 hours, whereas increasing the temperature from 40 to 60A degrees C had a negative effect.