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Molecular size and shape changes in waxy maize starch during dextrinization
Z. SUN (1), Y. Shi (2) (1) Kansas State University, Manhattan, KS, U.S.A.; (2) Kansas State University, , U.S.A..

The conformational properties of cold water-soluble pyrodextrin from insoluble native waxy starch were investigated using high performance size exclusion chromatography (HPSEC) coupled with multiple detectors for the first time. Pyrodextrin was prepared by adjusting waxy maize starch slurry pH to 2 or 3, filtering and drying at 40 °C, and then heating at 150 °C or 170°C for 0.5-4 h. The cold-water solubility of the pyrodextrin was from 64.7% to 100%. The gel permeation chromatography (GPC) results indicated that the molecular size was altered after dextrinization. At the end of dextrinization, the molecular weight was in the order of pyrodextrin at pH 3 and 150ºC  > pH 3 and 170ºC > pH 2 and 150ºC. The pyrodextrin with higher solubility in water had smaller molecular size, lower average molecular weight, lower intrinsic viscosity and lower hydrodynamic radius.  The measured Mark-Houwink a (0-0.5) indicated a spherical conformation of pyrodextrin in aqueous solution.