EXPLOITATION OF AGRI-FOOD SOLID WASTES FOR RECOVERY OF HIGH ADDED-VALUE COMPOUNDS: THE CASE OF GRAPE POMACE AND ONION PEELS

Abstract

Large quantities of both liquid and solid wastes are produced annually by the food processing industry. These waste materials contain principally biodegradable organic matter and their disposal creates serious environmental problems. The waste loads at the processing plant can be significantly reduced through the use of new or modified processing methods or through in-plant treatment and reuse and a variety of processes are being developed towards this direction, aiming at converting the waste materials into bio-fuels, food ingredients and other added-value bio-products. The scope of the present study was an examination on the possibilities of using non-toxic, cheap and readily available means of recovering phenolics from red pomace and onion peels. On such a basis, the solvent systems tested were composed of ethanol, a bio-solvent that can be obtained after fermentation of the sugar-containing raw materials and distillation. In the case of red grape pomace, simple media composed of 60% ethanol were shown to be ideal for recovery of extracts with increased polyphenol concentration and antiradical activity. Higher ethanol content (90%), however, was more effective for pigment extraction. For onion peels, extracts with high flavonol recovery and a reducing power were obtained with a similar medium (60% ethanol/ 0.1% HCl), while optimisation of the extraction conditions with regard to temperature and time, afforded higher yield and more active extracts.