Olive mill wastewater (OMW) originating from a two-phase olive oil producing plant was treated with a crude polyphenol oxidase (PPO) homogenate, prepared from potato waste peels. The treatments carried out were based on a 2 3-full-factorial, central composite design (CCD) in order to identify optimal operational conditions with regard to polyethylene glycol (PEG) concentration, pH, and treatment duration. The treatment performance was assessed by estimating the % reduction in total polyphenol (TP) concentration. The model obtained produced a satisfactory fitting of the data (2 = 0.96, = 0.0017). The utilisation of the predictive model enabled the theoretical calculation of the optimal set of conditions, which were pH = 4, = 3.57 h, and [PEG] = 900 mg L −1. Under these conditions, the optimal theoretical % removal calculated was 54 ± 9. Examination of the treated samples with high-performance liquid chromatography (HPLC) showed that the potato homogenate afforded changes in the polyphenolic profile. Based on the experimental evidence, oxidation pathways were proposed.

Plant food wastes and by-products might contain a range of enzymes capable of transforming bio-organic molecules, and thus they may have potential uses in bioremediation processes. Potato peels are an abundant plant food waste and might be considered a promising means of bioremediation since they contain the oxidative enzyme polyphenol oxidase (PPO), able to oxidize a range of pollutants. With this in view, this study aimed at investigating the influence of the side-chain structure of several o-diphenolic acids on their oxidizability by a crude potato peel PPO. After establishing optimal conditions concerning pH and temperature, the examinations carried out showed that the crude enzyme preparation used exhibited the highest catalytic efficiency with the physiological substrate, L-DOPA, which is an amino group-bearing o-diphenolic acid. Critical comparison of the data that emerged from testing chlorogenic acid (CGA), hydrocaffeic acid (HCA), and caffeic acid (CA) revealed that the unsaturation on the side chain might be a factor of instability for substrate binding, as judged by the particularly high K M for CA, but lack of double bond (HCA) or conjugation of the carboxyl group (CGA) restores stability. Based on the K M values determined, it was also shown that the higher the side-chain length, the lower the affinity between the substrate and the enzyme.

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