Water soluble chitosan-caffeic acid conjugates as a dual functional polymeric surfactant

A water soluble chitosan-caffeic acid conjugate (C-CAC) was prepared by chemical modification of chitosan using activated caffeoyl with dimethyl aminopyridine as a catalyst. The C-CAC was characterized using UV-visible spectrometry, Fourier transform infrared, nuclear magnetic resonance spectroscopies and differential scanning calorimetry. The caffeoyl content in the C-CAC was 65 mg/g. To study the introduction of a new function into chitosan, the antioxidant activities of the synthesized C-CAC was determined using three in vitro assays: DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)), and ferric reducing antioxidant power. The half inhibition concentration values for DPPH and ABTS radicals were 370 and 172 mu g/ml, respectively; showing its good radical scavenging activity. The emulsifying properties of the C-CAC were investigated by preparing 10% fish oil-in-water emulsions. C-CAC not only showed a good ability to stabilize oil-in-water emulsions, but also was more effective in retarding lipid oxidation compared to chitosan; implying that the synthesized C-CAC was functioning in an oil-in-water emulsion system as both emulsifier and antioxidant. Chitosan-phenolic conjugates, as a biopolymer-based surfactant, may represent a promising ingredient for enabling stable oxidation-sensitive oil-in-water emulsions.