Structure of pyrodextrin in relation to its retrogradation properties.

Pyrodextrins were prepared by heating waxy maize starch at 170°C and pH 3.0 for 0.5, 1, 2, 3 and 4h. Structural changes of pyrodextrins were determined by gel permeation chromatography and 1H NMR. Gelatinization and retrogradation of pyrodextrins were measured by differential scanning calorimetry. The water solubility of pyrodextrins increased from 48.9 to 99.4% as heating time increased from 0.5 to 4h. The molecular size, melting enthalpy of pyrodextrin, and the degree of retrogradation decreased as pyrodextrin solubility increased. The level of 1,6-anhydro-β-d-glucopyranose increased from 2.6 to 4.0% as the heating time increased from 0.5 to 4h. The degree of branching (DB) of pyrodextrins was increased from 8.8 to 14.4%, and the average chain length (CL) reduced from 7.2 to 4.6. The increased level of new bonds and DB combined with reduced CL during the dextrinization explained the reduced extent of retrogradation of the pyrodextrin.