Reuse potential of artichoke (Cynara scolimus L.) waste for the recovery of phenolic compounds and bioenergy

Artichoke waste was investigated as a potential source of phenolic compounds and bioenergy. The total phenolic content of the waste, expressed as gallic acid equivalents (GAE) per unit dry weight, was 32.2 mg GAE/g. Polyphenols were recovered from the waste by an environmentally friendly solvent extraction procedure using 50% (v/v) aqueous ethanol as solvent. Experiments were conducted according to a central composite design and response surface methodology was used to evaluate the effect of temperature (T), extraction time (E) and liquid-to-solid ratio (R) on the yield of phenolic extraction. Under optimal conditions (T = 53.3 °C, E = 110.4 min and R = 3.3 mL/g), over 90% of the phenolic compounds present in the waste were recovered. The three main factors T, E and R were all statistically significant and their influence on the extraction efficiency increased in the order: R < T < E. Artichoke waste was found to have high calorific value (HHV = 19.1 MJ/kg) and low ash content (A = 3.8 wt%). After phenolic extraction, HHV increased to 19.6 MJ/kg and A was reduced to 1.6 wt%. Overall, the results obtained strongly support the use of artichoke waste for the recovery of valuable phenolic compounds and the production of renewable bioenergy.