Artichoke waste as a source of phenolic antioxidants and bioenergy

The thermal properties of artichoke waste, a relatively rich source of phenolic antioxidants, were investigated before and after phenolic recovery in order to assess its suitability as a source of bioproducts and bioenergy. The two main fractions of the waste, the bracts and the stems, were submitted to solvent extraction with aqueous ethanol (0, 50, 100% v/v) and the resulting extracts were assayed for total phenolics, flavonoids and antioxidant activity. The polyphenol content of stems was 51.10 ± 0.74 mg GAE/g and that of bracts was 24.58 ± 0.57 mg GAE/g. Using 50% aqueous ethanol provided the highest extraction yields, with over 80% of phenolic compounds recovered. The higher heating value of artichoke waste was about 16 MJ/kg and changed very little after polyphenol extraction. The ash content of the two waste fractions was close to 5% (w/w) and was further reduced upon phenolic recovery. The elemental ash composition for the two fractions was very similar: silicon was the most abundant element (> 40% w/w) followed by phosphorus, calcium and potassium. Finally, TGA/DTG analysis showed no significant differences in the thermal properties of the extracted and unextracted materials, suggesting the possibility of recovering phenolic antioxidants from artichoke waste and bioenergy from the extraction residue. This could provide economic advantages to the artichoke industry and reduce its environmental impact.