In starch science, X-ray diffraction (XRD) has been solely used for the evaluation of starch type and/or the content of crystalline and non-crystalline (amorphous) materials in starch. However, XRD allows us to estimate the crystalline regularity and deficit. In this study, we newly propose a “crystalline index” of starch that was introduced by peak height and the full-width at half maximum (FWHM) by means of XRD to evaluate the destruction or discrimination of amylose and amylopectin in the starch production process of plants. Amylose, amylopectin, corn, potato and sago starch samples were used in this study. The crystalline index of amylose, amylopectin and other starch samples ranged from 609 to 1266, in the order of amylose > amylopectin > corn > potato > sago.

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 The sago palm (Metroxylon sagu) can accumulate 200 kg or more of starch per palm in its trunk. The characteristics of sago starch are different in the growing stages, portions of trunk, and cultivars. The differences between starch grains of non-spiny and spiny sago cultivars have not yet been fully characterized. In this study, an optical and scanning electron microscope, X-ray diffraction (XRD), and ¹³C cross-polarization/magic angle solid-state nuclear magnetic resonance (¹³C CP/MAS NMR) were used to analyze the structure of sago starch. The grain size of non-spiny sago starch was slightly smaller than that of the spiny one. The heated non-spiny sago starch samples showed that heating from 40 to 80°C resulted in the combining of 4a and 4b X-ray diffraction patterns, changing the reflecting face of the starch with a distance of 0.52 nm. The difference between non-spiny and spiny sago starches was not remarkable in ¹³C CP/MAS NMR spectra. The NMR signal peak of C₁ at 102 ppm increased with increasing heat temperature up to 80°C and decreased with increasing heating temperature after 80℃. It is concluded that the crystalline structures of non-spiny and spiny sago starches are affected by temperatures above 60°C based on the X-ray diffraction pattern and the fact that the conformation flexibility of the sago starch structure by heating was limited to the surface portion from the X-ray diffraction patterns and NMR spectra.

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