Synthesis of chitosan-caffeic acid derivatives and evaluation of their antioxidant activities |
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Authors: | Aytekin Ali Ozhan Morimura Shigeru Kida Kenji |
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Affiliation: | Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan. |
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Abstract: | In this study, the antioxidant activities of different molecular weights (Mw) and grafting ratios of chitosan–caffeic acid derivatives were investigated. The grafting process was achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC) as covalent connector under different conditions such as molecular-weight of chitosan, molar ratio of chitosan and caffeic acid, reaction temperature, pH, and reaction time. The half-inhibition concentrations (IC50) of products were calculated by reduction of the 1,1-diphenyl picryl hydrazyl in the radical-scavenging assay and reduction of the Fe3+/ferricyanide complex to the ferrous form in reducing power assay. The EDAC showed maximum activity at 3-h, pH 5.0 and room temperature conditions, except high-molecular-weight chitosan in pH 2.0. The products were water-soluble in all pH and showed lower viscosity than native chitosan. The highest grafting ratio of caffeic acid was observed at 15% in low-molecular-weight chitosan. After 5% grafting of caffeic acid into chitosan, the grafting efficiency was increased by decreasing molecular-weight of chitosan at the same conditions. Caffeic acid has main role in the antioxidant activity of products. The maximum IC50 of radical-scavenging activity (0.064 mg/ml) was observed at the highest caffeic acid containing derivative. Water-soluble chitosan and caffeic acid derivatives were obtained by this study without activity loss. |
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Keywords: | Chitosan Caffeic acid Grafting Antioxidant activity Reducing power |
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