Structural and molecular properties of dialdehyde starch

Dialdehyde starch (DAS) of degree of oxidation (DO) of 1.5% (DAS1-5), 5% (DAS5), 15% (DAS15) and 25% (DAS25) was prepared from potato starch in the periodate oxidation reaction with electrochemical recovery of the oxidant. Molecular weights (Mw) and radii of gyration (Rg) of polysaccharide chains of native and oxidized starches were measured by means of a high-performance size exclusion chromatography coupled with multiangle laser light scattering and refractive index detectors. The weight average molecular weight (Mw) and radius of gyration (Rg), calculated for the whole complicated peak of the eluate of native starch were 30.0×106 and 119.6 nm, respectively. The oxidation induced instant degradation of starch polysaccharide chains.Mw value of the chains of the polysaccharide molecules eluted from the sample of DO 1.5% (DAS1-5, 2.2×106) was by one order lower than the average molecular weight of native starch molecules (30×106). Even more significant decrease in molecular weight up to 6.4×104 was observed for the DAS5 sample. The chain length distribution of amylopectin structural units of native and DAS was characterized by the hydrolysis with isoamylase followed by treatment with β-amylase. Chain distribution profiles of completely debranched samples were available from a high-pressure size exclusion chromatography with multiangle laser light scattering and refractometric index detectors. The oxidation slightly changed the average molecular weight (Mw) of the A-type chains although it evoked changes in the mass ratio of the A-type chains. The weight average molecular weight Mw and mass ratio of B-type chains significantly differed depending on DO of the sample. X-ray diffraction patterns indicated that crystallinity of DAS1-5 and DAS5 decreased in relation to native starch. Oxidised starches of the highest DO were fully amorphous.