Isolation and Characterisation of Single Chain Amylose

Five amylose preparations of different origins (cassava, potato, smooth seeded pea, wheat and maize), obtained from native starch granules by thymol complexation, were ultracentrifuged as the final decontamination step to remove a high molecular weight population contaminating the amylose solutions. The efficiency of this ultracentrifugation procedure was assessed by dynamic light scattering (DLS): decreases in apparent hydrodynamic radii,R?_H, from 46·1–72·6 nm before ultracentrifugation to 16·1–29·3 nm after were observed. Amylose solutions were then characterised by size exclusion chromatography coupled on-line to multi-angle laser light scattering (SEC–MALLS). Under these conditionsM?_wof cassava, potato, smooth seeded pea, wheat and maize amyloses were, respectively, 1·05×10⁶, 7×10⁵, 6·2×10⁵, 5·1×10⁵and 3·4×10⁵g/mol. Using a specific optimisation algorithm, experimental molecular weight distributions (MWD) were fitted by two mathematical models of ‘Most Probable’ distribution and ‘log-normal’ distribution. The best fit was obtained for the second model, but fittedM?_wwere higher than experimentalM?_w. When a ‘Most Probable’ model was used, the fittedM?_wwere consistent with experimentalM?_wbut with a lower quality of fit. Exponentscin the power lawR_G=KM^cwere between 0·6 and 0·7, indicating an extended linear random coil in the range of MW analysed (3×10⁵–9×10⁶g/mol). This procedure was also applied to the characterisation of different commercial amylose products.