Linear starch and hexanoic acid complexation evaluated by isothermal titration calorimetry

Linear starch form inclusion complexes with fatty acids through hydrophobic interaction. The complexation between starch and fatty acid is affected by many factors, such as starch degree of polymerization (DP), fatty acid structure, and complexation conditions. There is limited information on the use of isothermal titration calorimetry (ITC) in understanding starch-fatty acid interactions. The effects of temperature and concentration of hexanoic acid on the complexation of debranched waxy maize starch and potato amylose were investigated using ITC. The starch samples were characterized for their molecular size distribution and iodine affinity. Potato amylose and debranched waxy maize starch displayed a major peak DP of 330 and 25, and iodine affinity of 2.9 and 13.9, respectively. The ITC titration data were fitted best to a one set of binding site model. Complexation was exothermic and spontaneous for all reactions based on changes in enthalpy of free energy (ΔG). The binding affinity (Ka) of debranched waxy maize starch for hexanoic acid decreased with an increase in temperature from 25 to 45°C. The Ka and number of binding sites (n) for debranched waxy maize exceeded those of potato amylose, indicating a higher complexation of debranched waxy maize for hexanoic acid. The number of binding sites (n) and enthalpy of binding (ΔH) values for both starches remained independent of temperature change. The ITC results demonstrated that debranched waxy maize starch was favored over potato amylose to complex hexanoic acid.