Crystallinity determination of amylose-fatty acid complex in gelatinized rice starch-fatty acid mixtures using Terahertz spectroscopy

The crystallinity of amylose-fatty acid complex can be one of the indicators for the glycemic index of rice products. X-ray diffraction (XRD), the standard method for measuring crystallinity, however, suffers from matrix effect. In this study, the potential of terahertz spectroscopy for determining the crystallinity of gelatinized rice starch after complexing with lauric acid (LA) and palmitic acid (PA), two fatty acids whose spectra overlap with XRD spectra of starch, was investigated. The crystallinities of amylose-fatty acid complex and trapped PA crystals were derived from XRD spectra. The crystallinity of amylose-fatty acid complex correlated with the intensity of the second derivative spectra at 12.0 THz. Furthermore, this peak did not overlap with the spectra of trapped PA peaks. These results indicate the intensity of the peak at 12.0 THz can be used to accurately and robustly determine the crystallinity of amylose-fatty acid complex in gelatinized rice starch-fatty acid mixtures without inference from the presence of LA and trapped PA in the sample matrix.