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In this study, protocatechuic acid (PA) was grafted onto chitosan (CS) by a carbodiimide mediated cross-linking reaction. The structural characterization, physical property and antioxidant activity of PA grafted CS (PA-g-CS) was investigated. As results, three copolymers with different grafting ratios (61.64, 190.11 and 279.69mg PAE/g) were obtained by varying the molar ratios of reaction substrates. PA-g-CS showed the same UV absorption peaks as PA at 258 and 292nm. As compared to CS, PA-g-CS exhibited a decreased band at 1596cm(-1) and a new band at 1716cm(-1), suggesting the formation of amide and ester linkages between PA and CS. New proton signals at δ6.77-7⋅33ppm were observed on (1)H NMR spectrum of PA-g-CS, assigning to the methine protons of PA. Signals at δ 150.8-116.6 ppm on (13)C NMR spectrum of PA-g-CS was assigned to the aromatic ring carbon of PA moieties. All the structural information confirmed the successful grafting of PA onto CS. SEM observation showed CS had a smooth surface, while PA-g-CS had a rough surface. TGA revealed the thermal stability of PA-g-CS was lower than CS. Antioxidant activity assays further verified the reducing power and DDPH radical scavenging activity of PA-g-CS was much higher than CS., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this study, novel chitosan (CS) based active films were developed by grafting natural phenolic antioxidant of protocatechuic acid (PA) onto chitosan backbones. The physicochemical, mechanical and antioxidant properties of three PA grafted CS (PA-g-CS) films with different grafting ratios were characterized. The transparent PA-g-CS films exhibited yellowish color with thickness ranging from 44.1 to 48.6 μm. By contrast with CS film, PA-g-CS films with medium and high grafting ratios showed decreased moisture content, water vapor permeability; however, increased water solubility and tensile strength. The barrier to UV light of CS film could be improved by grafting with PA. An increase in the total color difference was observed for PA-g-CS films, indicating PA-g-CS films were more colored. Among four kinds of films tested, PA-g-CS film with medium grafting ratio exhibited the highest tensile strength (45.7 MPa) and elongation at break (5.05%). According to thermogravimetric analysis, the maximum rates of weight loss for PA-g-CS films appeared at 291.8–294.0 °C. Antioxidant activity assays showed that PA-g-CS films had both dose-dependent and time-dependent scavenging activity on DPPH radical. Our results suggest that PA-g-CS films are expected to serve as novel antioxidant food packaging materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] Caffeic and ferulic acids were grafted onto chitosan by a free radical mediated method. [•] Copolymers had good free radical scavenging and peroxidation inhibition effects. [•] Copolymers significantly increased antioxidant enzymes activities and decreased malondialdehyde levels in d-galactose induced aging mice. [ABSTRACT FROM AUTHOR]

Abstract: In this study, three phenolic acids including gallic acid (GA), caffeic acid (CA) and ferulic acid (FA) were grafted onto N,O-carboxymethyl chitosan (NOCC) by a free radical mediated grafting method. The grafted copolymers obtained were all water-soluble samples. UV–vis absorption peaks of the grafted copolymers shifted toward longer wavelengths. FT-IR spectroscopy of the grafted copolymers exhibited additional phenolic characteristics of the aromatic ring C C stretching within 1450–1650cm−1. NMR spectroscopy of the grafted copolymers showed new peaks at 6.2–7.6ppm assigned to the phenyl protons of phenolic acids. These results all confirmed the successful grafting of three phenolic acids to NOCC. The conjugation probably occurred at amine of NOCC and carboxyl groups of phenolic acids. The grafted copolymers exhibited decreased crystallinity as compared to NOCC and chitosan. Moreover, antioxidant activity in vitro assays showed that the antioxidant property decreased in the order of GA-g-NOCC>CA-g-NOCC>FA-g-NOCC>NOCC>chitosan. Our results suggested the potential of phenolic acids grafted NOCC for the development of effective antioxidant agents. [Copyright &y& Elsevier]