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Introduction: Pecan nut processing results in the production of high amount of shells (40 to 50% by weight ), an industrial byproduct reddish in color, that may represent an alternative and sustainable source of compounds at high antioxidant capacity.1 We explored in this study the potential use of pecan nutshell (PNS) and its extracts for food applications. Material & Methods: PNS was ground by means of a blade mill through a 250 micron sieve. PNS extract was prepared by treatment of PNS with ethanol-water= 6/4 v/v. Polyethylene (PE) and polylactic acid (PLA) films containing PNS extract were prepared by extrusion. DPPH, FRAP, aging of oil samples, mushroom tyrosinase and apple browning inhibition assays were performed as described.2,3 Results: PNS exhibited efficient antioxidant activity in both the DPPH (EC500.3 Trolox equivalents) assays. A significant DDPH reduction was observed also with PLA and PE films containing 3% PNS extract. PNS significantly reduced iron-induced lipid peroxidation in cod liver oil-water emulsions. PNS extract efficiently inhibited dopa oxidation mediated by mushroom tyrosinase in a dose-dependent manner, with an IC50 value

Eumelanins, the black insoluble pigments of human skin, eyes and substantia nigra (neuromelanin), stand today as a unique source of inspiration for the design and implementation of soft biocompatible multifunctional materials for bio-optoelectronic devices. Interest in eumelanins stems from bioavailability, biocompatibility and a peculiar set of physicochemical properties, i.e. broadband absorption in the UV-visible range, intrinsic free radical character, water-dependent hybrid ionic-electronic conductor behaviour, supporting optimistic feelings about a possible rise of eumelanin-mimics as innovative bioinspired solutions for organic bioelectronics. However, a number of conceptual and technological gaps still hinder a rapid progress of melanin-based organic electronics and bioelectronics, including in particular the limited contribution of electronic conductivity and current decay with time under biasing. Herein, we provide a concise overview of the structural and optoelectronic properties of melanins with a view to bringing to focus main issues and challenges en route to bioelectronic applications. Copyright © Materials Research Society 2015.

Distal to tyrosinase activity, eumelanin synthesis is governed by the rearrangement of dopachrome which may proceed with or without decarboxylation giving 5,6-dihydroxyindole (DHI) and/or 5,6-dihydroxyindole-2-carboxylic acid (DHICA), that exhibit different chemical and biological properties. In melanocytes the reaction occurs under strict enzymatic assistance directing the course of melanogenesis toward DHICA and preventing the spontaneous decarboxylation to DHI. To inquire into the role of the carboxyl group as determinant of the chemical properties of the 5,6-dihydroxyindole system, DHICA and its methyl ester were compared for both their antioxidant activity and their conversion to eumelanin chromophores via oxidative polymerization. The results revealed that DHICA ester oligomers are stronger antioxidant compared to the free acid ones. Moreover, whereas the spectrophotometric course of DHICA oxidation proceeds via a purple chromophoric phase followed by band broadening to give a dark brown eumelanin, DHICA ester is converted to light brown species devoid of the typical euemelanin properties. These results suggest that the carboxyl group plays a more complex role than simply blocking the 2-position of the indole ring. The actual biological significance of these observations and their possible exploitation for dermocosmetic applications are currently under assessment in our laboratory.

Recent advances in the chemistry of melanins have disclosed the importance of the monomer composition in determining significant differences in the pigment properties of crucial relevance to their biological role, including skin (photo)protection and UV-susceptibility. In this scenario, a key role seems to be played by carboxyl groups. Depending on the extent of decarboxylation during the rearrangement of dopachrome different contents of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) can be incorporated into eumelanin pigments. Rearrangement of 5-S-cysteinyldopa o-quinoneimine likewise can lead to 1,4-benzothiazine (BTZ)or its 3-carboxylic acid (BTZCA) derivative. The DHICA-to-DHI ratio markedly affects the antioxidant and chromophoric properties of eumelanins: in particular, high amounts of DHICA-derived units decrease visible light absorption relative to DHI-based melanins, but markedly enhance antioxidant properties. In the same way carboxylated benzothiazines can confer pronounced visible and UVA absorption features to pheomelanins, accounting for light-dependent reactive oxygen species (ROS) production, whereas BTZ-related units seem to be more effective in inducing ROS production by redox cycling mechanisms in the dark. The possible biological consequences of carboxyl group retention in the eumelanin and pheomelanin pathways will be discussed.