SIMULTANEOUS DETERMINATIONS OF THE MOLECULAR-WEIGHT DISTRIBUTIONS OF AMYLOSES AND THE FINE-STRUCTURES OF AMYLOPECTINS OF NATIVE STARCHES

Native A (wheat and waxy rice), B (potato), and C (cassava and sweet p otato) types of starches were each debranched with isoamylase, and sep arated into amylose and amylopectin fractions by HPLC on size exclusio n columns coupled on-line to multi-angle-laser-light-scattering and di fferential refractometer detectors. The absolute molecular weights of amyloses and chain length distributions of amylopectins were determine d simultaneously, and pre-isolation of the amylopectin was not necessa ry. The molecular weights of debranched amylose from starches that hav e not been fractionated to separate amylose and amylopectin are signif icantly higher than published values for the undebranched fractionated amylose. The polymodal profiles of the refractive index chromatograms showed the complexity of the amylopectin structure of starches. The c hain length distribution of amylopectin depends critically on the meth od for analysing the broad chromatogram when determined by either noti ng the minima/inflections or deconvoluting the overlapping amylopectin fraction into numerous normal/Gaussian distributions. Although the re sults from the former (conventional) method of analysis were comparabl e with the literature values, they did not appear to be as sensitive a technique for detecting differences as the multiple Gaussian approach . Overall, the study suggested that the amylopectin chain units might be more complex than originally envisaged and that different degrees o f chain packing for the molecules can be inferred from this multiple c omponent analysis.