Macromolecular features of starches determined by aqueous high-performance size exclusion chromatography

Starches from various botanical sources, having different amylose-amylopectin levels, were treated with 95% (v/v) dimethylsulphoxide and then dissolved by microwave heating in a high pressure vessel (MWHPV). This procedure led to an almost complete dissolution of the starch sample when it was subsequently taken up in water. Various treatment times were tested, and optimal conditions corresponded to 35s heating time in MWHPV (maximum temperature 143 degrees C). Under these conditions, degradation of the polymers was not noticeable and the degree of solubilisation of starch in the samples was in the range 87 to 100%. High-performance size exclusion chromatography (KPSEC) in tandem with multi-angle laser light scattering and refractive index detection was used to investigate apparent weight-average molar mass ((M) over bar(W)) and z-average gyration radius ((R) over bar(G)) Of the starch components. Apparent (M) over bar(W) and (R) over bar(G) values for samples with different amylose contents (between approximate to 0 and 658%) were between 2.2 +/- 0.2 x 10(8) and 2.4 +/- 0.2 x 10(7) g/mol and between 250 +/- 10 and 163 +/- 5 nm, respectively. These values were higher than those reported previously(1,2) probably due to our more complete but less severe solubilisation procedure. When the heating time was increased from 35 to 90 s (maximum temperature 211 degrees C), the (M) over bar(W) and (R) over bar(G) decreased, demonstrating possible polymer degradation due to temperature. Partial precipitation of high amylose samples after 24h storage was detected by modifications in chromatograms, compared with freshly prepared samples. (C) 1998 Academic Press Limited.