Date of Award
Master of Science
Food Science and Technology
Joseph J. Bozell, Kevin Kit
Chitosan is the second most abundant natural polysaccharide in the nature. Due to its biodegradability and film forming ability, chitosan has the potential to be used as an alternative to petroleum-based polymers for food packaging. The presence of a primary amine as well as primary and secondary hydroxyl groups enable chitosan to be chemically modified with various functional groups. Gallic acid (GA) is a natural occurring antioxidant (AOX), which can be grafted to chitosan using by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The first project deals with the effect of ethanol (EtOH) concentration on efficiency of grafting GA onto chitosan. Using pure deionized water as a sole solvent (0% EtOH), GA grafted to chitosan at the largest extent (285.9 mg GA/g chitosan). As the concentration of EtOH increased, the grafting efficiency proportionally decreased. The nuclear magnetic resonance (NMR) studies showed that the higher alcohol concentration inhibited successful grafting of GA by prohibiting the conversion of the intermediate O-acylisourea ester to the expected intermediate NHS-ester. To assist the NMR studies of solvent effect on grafting, the formation of GA-NHS ester was investigated in the second study by quantitative 1H (proton) NMR reaction monitoring. Using a recently developed long-range heteronuclear single quantum multiple bond correlation (LR-HSQMBC),we were able to visualize a 5JCH (five-bond carbon-proton coupling) that confirmed the structure of the GA-NHS ester. The data showed that during grafting, a side reaction of crosslinking can occur as the hydroxyl groups of chitosan can be activated by EDC and coupled to the amino groups. In order to prevent the decreased solubility of chitosan caused by crosslinking, surface modification was introduced directly to chitosan films. The surface grafting was conducted utilizing EDC and NHS and was confirmed by FTIR. Surface grafted GA-chitosan films exhibited excellent AOX activity, assessed as 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging efficiency and reducing power. When used as packaging material, the surface-grafted chitosan films had similar or better effect as polyethylene films protecting sunflower seeds from lipid oxidation. Overall, this research has developed surface-grafted GA-chitosan films with excellent antioxidant efficiency that may be utilized as multifunctional biodegradable food packaging material.
Guo, Ping, "Gallic acid-grafted chitosan films as antioxidant food packaging. " Master's Thesis, University of Tennessee, 2015.