CHARACTERIZATION OF STARCHES DISSOLVED IN WATER BY MICROWAVE-HEATING IN A HIGH-PRESSURE VESSEL

Starch granules derived from four corn varieties were dispersed in water and depending on variety about 49-71% of the granules dissolved by microwave heating in a high pressure vessel (MWHPV). The apparent ratios of amylopectin to amylose were 1:0, 3:1, 1:1 and 3:7. High performance size exclusion chromatography (HPSEC) was carried out using two mu Bondagel(dagger) and one Synchropak(dagger) HPSEC columns placed in series. These had size exclusion limits specified by their manufacturers as 400 nm, 100 nm, and 10 nm, respectively. The mobile phase was 0.05 M NaNO3. For each starch composition, refractive index and viscosity chromatograms were obtained and fitted with the same six Gaussian components by nonlinear regression analysis. Calibration of the column set with pullulan and dextran standards in hydrodynamic volume and root mean square radius of gyration (R(g)) enabled calculation of the intrinsic viscosity (IV), molecular weight (M), and R(g) for each component in addition to global values of these quantities for the entire distribution. Analysis of the data revealed that as starches eluted from the column set, there were large changes in M and R(g) and rather small changes in IV. Furthermore, MWHPV containing water as employed here produces starch of relatively large molecular weight and size but low intrinsic viscosity leading to the conclusion that dense starch granule fragments were solubilized.