The interaction between wheat starch and pectin with different esterification degree and its influence on the properties of wheat starch-pectin gel

The interaction between wheat starch and pectin with different esterification degree (37%–73%) and its influence on the properties of wheat starch-pectin composite gel were investigated in the present study. It was found that high-ester pectin increased the swelling power (from 6.59 to 8.13 g/g) and solubility (from 7.12% to 8.83%) of wheat starch. Dynamic rheological results showed that high-ester pectin could maintain the viscoelasticity of composite gels, while low-ester pectin significantly reduced the viscoelasticity of composite gels. In addition, the composite index (CI) of high-ester pectin and wheat starch could reach 47.29%, which was significantly higher than that of low-ester pectin and wheat starch (23.27%). High-ester pectin (DE = 73%) significantly increased enthalpy (ΔH, from 0.72 to 1.09 J/g), relative crystallinity (from 2.03% to 3.41%) and the degree of short-range order (from 0.6441 to 0.8222) and enhanced the inter-strand hydrogen bond and inter-double helices hydrogen bond. These results indicated that high-ester pectin was more likely to interact with wheat starch to make the internal structure of the composite gels more stable and orderly. The results were also confirmed by the more compact and regular wheat starch-pectin (DE = 73%) gel network structure in SEM. Moreover, the results of intermolecular forces suggested that wheat starch and pectin mainly interacted through hydrogen bonds.