Cereal Chem 65:443-446   |  VIEW ARTICLE

Starch Gelatinization: An X-ray Diffraction Study.

H. F. Zobel, S. N. Young, and L. A. Rocca. Copyright 1988 by the American Association of Cereal Chemists, Inc. 

Starch gelitinization was defined as the melting of starch crystallites, as determined by X-ray diffraction, in which the complete destruction of crystallite integrity was observed as a function of moisture content and temperature. Melting occurred over a range of temperatures, and melting temperatures increased as starch moisture content decreased. For moisture contents of 30% and higher, endothermic transitions determined by calorimetry were confirmed as reflecting loss of starch crystalline structure. The wide range of melting temperatures was attributed to different degrees of crystallite perfection within the granule and to their respective interaction with granule moisture content. For normal maize starch, heating caused formation of crystalline V-type complexes of amylose with granule fatty acids. Formation of these complexes partly explains differences reported for heat of gelatinization values of amylose/lipid-bearing starches because of competing melting and crystallizing effects. X-ray analysis failed to confirm differential scanning calorimetry evidence of starch melting in samples at moisture contents lower than about 30% and heated to temperatures as high as 175 C. A glass transition was postulated to account for reports of apparent differential scanning calorimetry endotherms in such low-moisture starches. In the absence of an intermediate amorphous melt, the B to A or C structure changes observed in heat and moisture treated potato starches were interpreted as solid-state transitions.