Polyphenols Extraction from Hazelnut Skin Using Water as Solvent: Equilibrium Studies and Quantification of the Total Extractable Polyphenols

In this work, a system for the extraction of antioxidant agents from waste vegetal matrices was studied. To this end, the extraction of polyphenols from food waste hazelnut skins was taken into consideration as a case study and a continuous set-up using distilled water at 70 °C as a solvent has been developed. Various extraction cycles were performed at different solid/liquid ratios (ranging from 2 to 5.7 g/l) in order to study the effect of this parameter on extraction efficiency. Through a mass balance, data obtained from the various cycles were used to calculate the total extractable polyphenols, and a value of 0.114 g of polyphenols per g of hazelnut skin was evaluated. Moreover, for two selected cycles the polyphenols concentration in the aqueous solution was measured at different time intervals in order to determine the extraction time, and in both tests it reached a plateau within the first hour. Finally, equilibrium concentrations of polyphenols in liquid and solid phases of the six tests were correlated by a linear isotherm equation, and a partition coefficient of 0.0368 l/g was evaluated through a fitting of experimental data