Rheological and antioxidant power studies of enzymatically grafted chitosan with a hydrophobic alkyl side chain

The enzyme-mediated grafting of hydrophobic alkyl side chains onto Chitosan (Ch) has been successfully achieved using octyl gallate and horseradish peroxidase. The properties of the resulting materials have been studied by rheology and electron paramagnetic resonance (EPR) spectroscopy in order to envisage its potential applications as bioactive food additive. The chemical structures of the octyl gallate-grafted Ch were corroborated by ATR-FTIR, 1HRMN, viscosimetric molecular weight and ζ potential. The antioxidant capacity of materials determined by EPR show that functionalized Ch radical scavenging increases with grafting, which was related to the aromatic ring in the octyl gallate. The Ch with the highest grafting exhibited an antioxidant capacity of 81%. Solutions of the materials in acetic acid and lactic acid exhibited a shear-thinning flow behavior which also increased with the grafting. The viscoelastic properties of solutions were characterized by oscillatory shear measurement and the result showed fluid-like viscoelastic behavior. The elasticity of the solutions decreased with the plasticizer addition.