Treatment with boiling 6 M HCl increases up to 30 times the intrinsic antioxidant potency of spent coffee grounds, leading to a versatile multifunctional material (hydrolyzed spent coffee grounds, HSCG). Spectral and morphological analyses suggest that the remarkable potentiation of the antioxidant activity is due to efficient removal of the hydrolyzable components, mainly carbohydrates, making the polyphenol-rich component available for interaction with free radicals and oxidizing species. HSCG efficiently protects hepatocarcinoma (HepG2) cells from oxidative stress-induced injury and delays lipid peroxidation in fish and soybean oils. Moreover, films made of polyethylene/2% HSCG blends display greater stability to thermal and photo-oxidative degradation. HSCG may thus represent an easily accessible and sustainable alternative to currently available biomaterials with intrinsic antioxidant properties for biomedical, industrial, and technological applications

Resveratrol is a naturally occurring polyphenol, well known as a nutritional supplement due to its strong antioxidant properties associated with anti-inflammatory activity and possible prevention of cardiovascular diseases. In this work, the effect of resveratrol on thermal, thermooxidative, and photo-oxidative degradation of polylactide is reported in the frame of developing fully biobased polymer formulations. Characterization of PLA films by thermal methods and photo-oxidative treatments demonstrated that resveratrol catalyzed high temperature transesterification reactions under inert atmosphere, whereas it efficiently inhibited the exothermal oxidative reactions of the polymer backbone. Lowtemperature photochemical degradation experiments on PLA films allowed elucidating the stabilization mechanisms of the phenolic additive. Resveratrol is capable of slowing the oxidative chain reaction of PLA through a peroxyl radicals scavenging mechanism, while it has little effect on the direct photolytical cleavage of the ester bonds. Moreover, direct resveratrol oxidation as well as the reaction between the phenol and photo-oxidized polymer species yield secondary photoproducts, which are also able to protect PLA against photo-oxidation likely due to the UV screening effect of the formed chromophores. Resveratrol is thus proposed as an eco-friendly and biocompatible additive for a sustainable approach to the stabilization of PLA films in packaging and other applications.

Recovery of functional molecules from byproducts of agro-food industries is an appealing approach to waste reduction and to obtain safe and value-added phytochemicals with antioxidant and antimicrobial properties. However, more information about the operational costs is needed for successful industrial scale-up. In this study, the potential of pecan (Carya illinoinensis) nutshell (NS) as a source of antioxidants was investigated. To this aim, a hydroalcholic NS extract (NSE) was thoroughly characterized, and its effect was investigated on thermo- and photo-oxidative stability of two polymers widely used in food packaging, polylactic acid (PLA) and polyethylene (PE). Twenty-six phenolic constituents, including proanthocyanidins, were identified in NSE, and its effective radical scavenging capacity was assessed. NSE acted as a thermal stabilizer for PLA and PE films, both in an oxygen-depleted environment (i.e., during melt processing) and in the presence of oxygen during polymer service life. NSE showed great potential as a PLA stabilizer, due to the compatibility with the polyester matrix. Under UV-light irradiation, NSE was more effective in protecting PE than PLA, due to combination of peroxy radical scavenging and inhibition of Norrish-type photolytic cleavage. Finally, from the experimental data, an economic evaluation of batch and continuous mode NSE manufacturing was performed, demonstrating that the process is technically and economically viable. Overall, these results emphasize the potential of NSE as a low-cost, safe, and sustainable additive for the stabilization of polymer films in packaging and other applications.

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Herein, the antioxidant and food stabilizing properties of a pecan nut shell (PNS) hydroalcoholic extract (PNSE) are reported. Chemical degradation of PNSE demonstrated the presence of condensed tannins as the main phenolic components. PNSE showed remarkable antioxidant properties in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay (EC 50 = 0.004 mg/mL). PNSE was initially tested as an inhibitor of mushroom tyrosinase, exhibiting a quite low IC 50 value (0.055 mg/mL) against the enzyme diphenolase activity, suggesting its use in enzymatic browning inhibition. The anthocyanin stabilization properties were evaluated under accelerated aging conditions of both pure pigments and commercial fruit juices, and PNSE was found to be effective at concentrations (0.05 mg/mL) at which well-known stabilizers such as chlorogenic and ferulic acids proved to fail. PNSE also performed well in the stabilization of spray-dried anthocyanins for use as a food colorant, increasing the half-life of blackberry anthocyanins up to 20%. In order to explore the possibility of using PNSE as a functional additive for active packaging, polylactic acid (PLA) films containing PNSE were prepared by solvent casting, and no substantial alteration of the mechanical properties was found on addition of the extract up to 10% w/w. The films showed remarkable antioxidant properties (DDPH reduction >60% with a 3% w/w loading, at a dose of 1 mg/mL in the DPPH solution) and delayed the onset of browning of apple smoothies (ca. 30% inhibition with a 10% w/w loading). These results highlight the exploitation of PNS as a low-cost polyphenol source for food industry applications.

Largely produced agri-food byproducts represent a sustainable and easily available source of phenolic compounds, such as lignins and tannins, endowed with potent antioxidant properties. We report herein the characterization of the antioxidant properties of nine plant-derived byproducts. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays indicated the superior activity of pomegranate peels and seeds, grape pomace and pecan nut shell. An increase in the antioxidant potency was observed for most of the waste materials following a hydrolytic treatment, with the exception of the condensed tannin-rich pecan nut shell and grape pomace. UV-Vis 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. 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, 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 open new perspectives toward the exploitation and manipulation of agri-food byproducts for application as antioxidant additives in functional materials.

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