Abstract
Tannins have always been the subject of great interest for their countless properties, first of all their ability to produce functional coatings on a variety of materials. We report herein a comparative evaluation of the antioxidant properties of wood tannin-based coated substrates. In particular, nylon membrane filters were functionalized with chestnut (hydrolyzable) or quebracho (condensed) tannins by dip coating under different conditions. The efficiency of functionalization was evaluated by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays, which invariably highlighted the superior ability of condensed tannins to induce the formation of a functional and robust coating. The results of the antioxidant assays revealed also the deleterious effects of aerial or enzymatic oxidation conditions on substrate functionalization, being more significant in the case of hydrolyzable tannins. On the other hand, the use of oxidizing conditions allowed to obtain more stable coatings, still exhibiting good antioxidant properties, in the case of condensed tannins. The presence of iron ions did not lead to a significant improvement of the coating efficiency for either tannins. The systematic approach used in this work provides novel and useful information for the optimal exploitation of tannins in antioxidant functional coatings.
Highlights
Tannins occupy a prominent role among natural phenolic compounds due to their remarkable antioxidant, antimicrobial, and anticancer activities [1,2,3]
The laccase used in this study was the recombinant POXA1b from the fungus Pleurotus ostreatus heterologously produced in the yeast Pichia pastoris [28]
Weak or no linear correlations were observed between the percentage of DPPH reduced and the amount of tannin adhered to the nylon filter (Figure S3), suggesting that it is not the amount of coating material to determine the efficacy of the functionalized substrate as an antioxidant, but likely the chemical structure of the coating species
Summary
Tannins occupy a prominent role among natural phenolic compounds due to their remarkable antioxidant, antimicrobial, and anticancer activities [1,2,3]. Tannins are widely distributed in the plant kingdom, but the most industrially exploited are those deriving from wood, from Castanea sativa (chestnut) and Shinopsis lorentzii (quebracho) hardwood These are traditionally classified as hydrolyzable or condensed (non-hydrolyzable) tannins. Of wood tannins are to be it is well-established that coating properties of wood bondings tannins areand to be ascribed to ascribed to their ability to interact with macromolecules by hydrogen hydrophobic their ability to interact with macromolecules by hydrogen bondings and hydrophobic interactions interactions [26,27], a comparative investigation between hydrolyzable and condensed wood tannins [26,27], a comparative between hydrolyzable condensed wood tannins for the for the development of investigation functional antioxidant coatings is, toand the best of our knowledge, lacking in development of functional antioxidant coatings is, to the best of our knowledge, lacking in the literature On this thisbasis basiswewe report a comparative evaluation of the antioxidant of.
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