A method for estimating the nature and relative proportions of amorphous, single, and double-helical components in starch granules by (13)C CP/MAS NMR.

An improved method to analyze the (13)C NMR spectra of native starches, which considers the contribution of the V-type conformation and the nature of the amorphous component, has been developed. Starch spectra are separated into amorphous and ordered subspectra, using intensity at 84 ppm as a reference point. The ordered subspectra of high amylose starches show the presence of both V-type single helices and B-type double helices. Relative proportions of amorphous, single, and double-helical conformations are estimated by apportioning intensity of C1 peak areas between conformational types on the basis of ordered and amorphous subspectra of the native starch. Quantitative analysis shows that the V-type single-helical component increases with amylose content of starches. Different amorphous subspectra are needed to provide a consistent analysis of granular starches from diverse sources. The method of preparation was found to be more important than the starch botanical origin in determining (13)C NMR spectral features of amorphous samples.