48 Initial heat treatment influences amylopectin retrogradation.

D. B. THOMPSON. Department of Food Science, 111 Borland Laboratory, The Pennsylvania State University, University Park, PA 16802.

Amylopectin (AP) retrogradation subsequent to gelatinization is known to be related to the moisture content and temperature of storage. We have recently shown that the temperature of the initial heat treatment to effect gelatinization also strongly affects retrogradation kinetics for waxy-type maize starches. Our research has focused on four waxy-type maize starches (from the wx, ae wx, du wx, and su2 wx endosperm genotypes) with known differences in AP structure. In every case the most rapid retrogradation was observed after heating to a temperature just sufficient to complete the gelatinization process as determined by differential scanning calorimetry (DSC). The moisture level at which maximum retrogradation enthalpy was observed, and the rate of retrogradation, varied among these four starches. Analysis of DSC thermograms as retrogradation enthalpy developed over time has led to mechanistic hypotheses relating retrogradation behavior to AP structure. We suggest that residual granule order is maintained at temperatures above the conclusion of gelatinization as observed by DSC, and the extent of this residual order diminishes as the temperature increases. An effect is observed for temperatures far higher (>140?C) than commonly thought necessary for gelatinization of a waxy starch.