| Considering the serious environmental problems induced by the conventional food packaging materials,there is an urgent need to develop an economical,convenient,nature-reproducible,environment-friendly and biodegradable food packaging.In this work,chitosan(CS)was dissolved in water with the aid of hydroxybenzotriazole(HOBt)and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide(EDC)served as a cross-linker,eventually five different kinds of phenolic acids were grafted onto chitosan(CS)chain,respectively.The substituted ratio,structural characterization and biochemical property of the five phenolic acids-chitosan conjugates were investigated.Gallic acid-chitosan conjugate was proved to have excellent features and popular price,eventually,acting as film former.Consequently,the physical features,functional properties(antioxidant and antimicrobial activities)and microstructures of CS film,GA-CS films and GA-g-CS films were comparatively studied.The experimental results were collated systematically as follow:1.Synthesis and structural characterization of five phenolic acids-chitosan conjugatesGallic acid(GA)/vanillic acid(VA)/ferulic acid(FA)/chlorogenic acid(CGA)/caffeic acid(CA)-chitosan conjugates were synthesized by introducing GA/VA/FA/CGA/CA onto chitosan with the aid of EDC and HOBt,respectively.The grafting ratio of GA/VA/FA/CGA/CA-chitosan conjugates reached up to 163.1 ± 0.83 mg GAE/GA-g-CS?46.7±0.67mg VAE/VA-g-CS?52.4±0.50mg FAE/FA-g-CS?144.8±1.03 mg CGAE/CGA-g-CS?99.0±2.30 mg CAE/CA-g-CS.The datas of UV-vis?FT-IR and 1H NMR for phenolic acids-chitosan conjugates demonstrated the successful conjugation of phenolic acids onto chitosan.2.Research on the antioxidant and the inhibitory effects on bacteria of phenolic acids-CS conjugatesThe results of the antioxidant effect in the chemical evaluation system showed that phenolic acids-CS conjugates owned excellent scavenging activities on 2,2-diphenyl-1-picrylhydrazyl(DPPH),superoxide and 2,2'-azino-bis-(3-ethylbenzo thiazoline-6-sulphonic acid)(ABTS)radicals,metal ion chelating activity,inhibitory effects on lipid peroxidation and ?-carotene-linoleic acid bleaching assay and powerful reducing power.The antioxidant capacity decreased in order of GA-g-CS,CGA-g-CS,CA-g-CS,FA-g-CS and VA-g-CS.The phenolic acids-chitosan showed an effective inhibition on Bacillus cereus(CGMCC 1.895)?Escherichia coli(CGMCC 7.59)?Salmonella typhimurium(CGMCC 1.10754)?Staphylococcus aureus(CGMCC 1.8721)?Bacillus subtilis(CGMCC 1.4255)?Shigella(CGMCC 1.10599)?Listeria monocytogenes(CGMCC 1.9144)and Pseudomonas aeruginosa(CGMCC 1.10274).The inhibitory effects decreased in the order of CGA-g-CS,GA-g-CS,CA-g-CS,FA-g-CS and VA-g-CS.GA-g-CS was selected as film former in consideration of the fact that GA was more cheap and accessible than CGA.3.Comparative research on the features of three kinds of composite filmsThe physical features,functional properties(antioxidant and antimicrobial activities)and microstructures of the native CS/gelatin composition film,GA/CS/gelatin composition film and GA-g-CS/gelatin composition film were comparatively investigated.With the growth of GA concentration,there was an increase in water solubility,tensile strength,Young's Modulus,antioxidant and antimicrobial activities,and dark color,whereas the WVP,transmittance and elongation at break for the GA/CS/gelatin composition films declined.Different from GA/CS/gelatin composition films,the GA-g-CS films exhibited enhanced WVP with the substitution degree of GA increasing.Meanwhile,TS and the solubility in water decreased.Although the mechanical characteristics and water resistance of the GA/CS/gelatin composition film was superior to that of the GA-g-CS/gelatin composition film,the antioxidant and antimicrobial activity of the former were inferior to the latter.Scanning electron and atomic force microscope were performed to observe the microstructures of films and there were some differences among the three composition films.The formation of a flat,smooth and compact structure was observed for the surface of the native CS/gelatin composition film.For the GA/CS/gelatin composition films,there were some GA crystals and products resulting from the affinity interaction between GA and gelatin,evenly dispersing on the surface.Meanwhile,the GA-g-CS/gelatin composition films exhibited rugous surface microstructure.There were certain relationships in microscopic surface morphology and the prepared films properties. |
PDF Full Text Request