Complexation behavior of octenyl succinic anhydride starch with chitosan

Abstract This study investigated the complexation behavior of octenyl succinic anhydride (OSA) starch (OSA-S) and chitosan (CS). According to the analysis of the turbidity, ζ-potential, optical micrographs and state diagrams, a pH-induced phase transition occurred due to the modification of the surface charge in biopolymers through ionic group dissociation. The aggregation of biopolymers was then altered to exhibit different complexation states, including co-soluble mixtures as well as soluble and insoluble complexes. An increase in substitution degree (DS) of OSA-S or OSA-S/CS mixing ratios changed the charge balance between biopolymers during complexation, leading to increased turbidity and a charge compensation-shift. The impacts of ionic strength, urea concentration, temperature and reaction time on the complexation behavior were also explored. In addition to the electrostatic interaction, hydrogen bonding and hydrophobic effects may also be involved in the complexation of OSA-S and CS. This was verified by fourier transform infrared spectroscopy and isothermal titration calorimetry. A spontaneous exothermic process of complexation was also observed by calorimetry. The information presented in our study may assist in developing polysaccharide complexes based on the comprehension of their complexation behavior.