Carboxymethyl Chitosan Case Study

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Effect of γ-rays on carboxymethyl chitosan for use as antioxidant and preservative coating for peach fruit
Ahmed M. Elbarbarya* and Tahia B. Mostafab a Polymer Chemistry department, National Center for Radiation Research and Technology, Nasr City, Cairo, Egypt b College of Women, Ain Shams University, Cairo, Egypt
Carboxymethyl chitosan (CMCS) was synthesized by alkylation of chitosan using monochloroacetic acid and characterized by FTIR and 1H-NMR spectroscopy. Different molecular weights (Mw) of CMCS were prepared by radiation degradation of CMCS in the solution form at different irradiation doses. The structural changes and Mw of degraded CMCS were confirmed by UV-Vis, FTIR and GPC. The antioxidant activity of CMCS were evaluated
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2.1. Materials and Methods
Chitosan, DD 85%, Mw 420 kDa, Aldrich. 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4’,4’’-disulfonic acid sodium salt (Ferrozine) were purchased from Sigma Chemicals. EDTA, ferric chloride and ferrous chloride were supplied from BDH. Potassium ferricyanide was supplied from Riedel laboratory reagents. Thiobarbituric acid, monochloroacetic acid and trichloroacetic acid were supplied from SUVCHEM laboratory chemicals. Other reagents and solvents were of analytical grade.
2.1. Preparation of CMCS
The carboxymethylation process of CS into water soluble CMCS was carried out according to the method reported previously (Qian et al., 1996; Chen, et al., 2004). Briefly, CS powder (10 g) was suspended in 100 ml of isopropyl alcohol and the resulting slurry was stirred in a 500 ml flask at room temperature. 25 ml of 10 N aqueous NaOH solution, divided into five equal portions, was then added to the stirred slurry over a period of 25 min. The alkaline slurry was stirred for additional 30 min. Subsequently, monochloroacetic acid (60 g) was added, in five equal portions, at 1 min intervals. Heat was then applied to bring the reaction mixture to a temperature of 60 oC and stirring at this temperature was continued for 3 h. Afterward, the reaction mixture was filtered and the filtered solid product (CMCS) was thoroughly rinsed with methanol. The resultant CMCS was dried in an oven at 60 oC. The Mw of the produced
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Briefly, 1.5 ml of DPPH solution (0.1 mM, in 95 % ethanol) was incubated with different concentrations of unirradiated and irradiated CMCS solutions. The reaction mixture was shaken well and incubated for 15 min at room temperature and the absorbance of the resulting solution was read at 517 nm against a blank (control). Ascorbic acid was used for comparison as antioxidant materials. The radical scavenging effect was measured as a decrease in the absorbance of DPPH and can be calculated using the following

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