Surfactant-mediated solubilisation of amylose and visualisation by atomic force microscopy

The starch polysaccharide amylose has been visualised at the molecular level by atomic force microscopy (AFM). In order to image individual amylose chains, a new method was developed for producing aqueous amylose solutions at room temperature. The method involved incubation of hot amylose solutions with iodine and the non-ionic surfactant Tween-20 (polyoxyethylene sorbitan monolaurate). This process stabilises the amylose molecules such that, after cooling to room temperature, no aggregation takes place. AFM images of the resulting sample revealed a distribution of extended chain-like molecules, and allowed for the first time, direct visualisation of a small number of branched macromolecules. Treatment of the sample with the starch-degrading bacterial α-amylase (EC 3.2.1.1) confirmed the nature of the soluble chain-like polymers.