Molecular characteristics of oxidized and cross-linked lotus (Nelumbo nucifera) rhizome starch

Lotus rhizome starch was isolated and subjected to chemical modification using different levels of oxidation, cross-linking, and dual modifications. Fourier transform infrared (FTIR) and X-ray diffraction analyses confirmed the successful modification of native starch. The carbonyl, carboxyl contents, and degree of cross-linking of modified starch were in the range of 0.03-0.07%, 0.07-0.15%, and 4.31-58.28%, respectively, for oxidized, cross-linked, and dual-modified starches. Amylose content varied from 13.57% to 20.60% for native and modified starches. Swelling power (SP) and solubility were temperature dependent and increased with increase in temperature. Oxidation and dual modification increased solubility, while cross-linking decreased solubility. Paste clarity, degree of crystallinity, and whiteness of starches increased significantly with increase in level of modifications. Peak, breakdown, and setback viscosities of the modified starches decreased with increase in modification. Phase transitions using DSC presented lower enthalpy values for modified starches. Gelatinization temperature increased due to modification whereas scanning electron micrographs revealed that modification altered the starch morphology.