Interactions between hsian-tsao gum and chitosan in aqueous solution

Abstract

The interactions of 0.05 wt% chitosan (CS) in admixture with different amounts of hsian-tsao gum (HG) in aqueous solutions were studied under different pH and ionic strength by the analysis of state diagram, turbidity, particle size and distribution, zeta potential and microstructure. Results obtained suggested that interactions between CS and HG could form soluble/insoluble complexes mainly through electrostatic attractions which significantly affected by HG concentration, pH and ionic strength. Particularly, varying pH or increasing HG concentration affected the zeta potential of CS-HG mixtures, which further influenced the complexes formation and caused phase separation. Furthermore, the formation of soluble complexes occurred between individual CS and HG molecules at pH away form pKa of CS, near which insoluble complexes with bigger size formed between HG and aggregate CS, except the 0.005 wt% HG molecules interacted with aggregate CS to form soluble complexes with smaller size than CS alone at pH 6.5. Additionally, added NaCl ions changing the charge density of two biopolymers further affected their electrostatic interactions, which were enhanced at lower concentrations but suppressed at higher concentrations. Optical measurements indicated the CS-HG complexes formed at pH 6.5 presented a coarsening phenomenon with increase of HG concentration. This study provided information regarding the effects of HG concentration, pH and ionic strength on the formation of electrostatic complexes between CS and HG in aqueous solution, which could be an available reference for preparation of electrostatic complexes.