Systematic Investigation of the Antioxidant Properties of Agri-food Byproducts and Characterization of the Effects of Hydrolytic Treatments

Systematic Investigation of the Antioxidant Properties of Agri-food Byproducts and Characterization of the Effects of Hydrolytic Treatments We report herein the results of a systematic evaluation of the antioxidant properties of a series of plant-derived byproducts, selected among those produced in largest amounts by the agri-food industry, which represent a cheap, sustainable and easily available source of phenolic compounds, such as lignins and tannins.1,2 In particular, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays indicated the superior activity of pomegranate peels and reducing/antioxidant power (FRAP) assays indicated the superior activity of pomegranate peels and seeds, grape pomace and pecan nut shell. The effects of an acid hydrolytic treatment previously applied to other agri-food wastes to improve the antioxidant properties3,4 were also evaluated. An increase in the antioxidant potency was observed for most of the waste materials following this treatment, with the exception of the condensed tannin-rich pecan nut shell and grape pomace. UVVis and HPLC investigation of the soluble fractions coupled with the results from IR analysis and chemical degradation approaches on the whole materials allowed to conclude that the improvement of the antioxidant properties was due not only to removal of non-active components (mainly carbohydrates), but also to structural modifications of the phenolic compounds.5 Parallel experiments run on natural and bioinspired model phenolic polymers suggested that these structural modifications positively impacted on the antioxidant properties of lignins and hydrolyzable tannins, enhancing their H-atom and electron donor properties, whereas significant degradation of condensed tannin moieties occurred, likely responsible for the lowering of the reducing power observed for grape pomace and pecan nut shell. These results put the basis for a rational exploitation and manipulation of agri-food byproducts for application as antioxidant additives in functional materials.