ISOLATION AND CHARACTERIZATION OF SINGLE-CHAIN AMYLOSE

Five amylose preparations of different origins (cassava, potato, smoot h seeded pea, wheat and maize), obtained from native starch granules b y thymol complexation, were ultracentrifuged as the final decontaminat ion step to remove a high molecular weight population contaminating th e amylose solutions. The efficiency of this ultracentrifugation proced ure was assessed by dynamic light scattering (DLS): decreases in appar ent hydrodynamic radii, (R) over bar(H), from 46.1-72.6 nm before ultr acentrifugation to 16.1-29.3 nm after were observed. Amylose solutions were then characterised by size exclusion chromatography coupled on-l ine to multi-angle laser light scattering (SEC-MALLS). Under these con ditions (M) over bar(w) of cassava, potato, smooth seeded pea, wheat a nd maize amyloses were. respectively, 1.05 x 10(6), 7 x 10(5), 6.2 x 1 0(5), 5.1 x 10(5) and 3.4 x 10(5) g/mol. Using a specific optimisation algorithm, experimental molecular weight distributions (MWD) were fit ted by two mathematical models of 'Most Probable' distribution and 'lo g-normal' distribution. The best fit was obtained for the second model , but fitted, (M) over bar(w) were higher than experimental (M) over b ar(w). When a 'Most Probable' model was used, the fitted (M) over bar( w), were consistent with experimental (M) over bar(w) but with a lower quality of fit. Exponents c in the power law R(c)=KM were between 0.6 and 0.7, indicating an extended linear random coil in the range of MW analysed (3 x 10(5)-9 x 10(6) g/mol). This procedure was also applied to the characterisation of different commercial amylose products. (C) 1996 Academic Press Limited