Enzymatic removal of phenols from aqueous solution by artichoke (Cynara scolymus L.) extracts

The effects of extracts from artichoke (Cynara scolymus L.) flower bracts on model wastewaters containing a range of phenolic contaminants have been studied. The extracts contained various isoenzymes of both peroxidase (POD) and polyphenol oxidase (PPO). HPLC measurements showed that the monophenol, 4-chlorophenol, was most effectively oxidized in the presence of both extract and hydrogen peroxide (H2O2), suggesting that this substrate was mainly being acted upon by POD. In similar experiments with l-dopa, an o-diphenol, the presence of H2O2 was not required for the efficient formation of insoluble melanins as PPO was more active in this case. Agitation of the reaction mixture favored oxidation by PPO by ensuring an adequate supply of oxygen to the enzyme. Conversely, bubbling with nitrogen greatly reduced PPO activity but did not affect POD. Some care was required to avoid the presence of large excesses of H2O2, which could lead to the inactivation of the enzymes. The results indicate that using a mixture of enzymes (and possibly also non-enzymic constituents) such as that found in artichoke extract, makes wastewater treatment with extract more effective and flexible than using either POD or PPO alone. Furthermore, artichoke extract was easy and simple to produce from a low value source making the method highly economical.