Retrogradation of maize starch after thermal treatment within and above the gelatinization temperature range

Studies of starch retrogradation have not considered the initial thermal treatment. In this article, we explore the effect of heating to temperatures within and above the gelatinization range on maize starch retrogradation. In the first experiment, 30% suspensions of waxy (wx) starch were initially heated to final temperatures ranging from 53 to 72 degrees C and held for 20 min. On reheating in the differential scanning calorimeter immediately after cooling, the residual gelatinization endotherm peak temperature increased, the endotherm narrowed, and enthalpy decreased. Samples stored for seven days at 4 degrees C showed additional amylopectin retrogradation endotherms. Retrogradation increased dramatically as initial holding temperature increased from 60 to 72 degrees C. In a second experiment, wx starch was initially heated to final temperatures from 53 to 180 degrees C and rapidly cooled, followed by immediate reheating or storage at 4 degrees C. Maximum amylopectin retrogradation enthalpy after storage was observed for initial heating to 82 degrees C. Above 82 degrees C, retrogradation enthalpy decreased as initial heating temperature increased. A similar effect for ae wx starch was observed, except that retrogradation occurred more rapidly than for Hx starch. These experiments show that heating to various temperatures above the range of gelatinization may profoundly affect amylopectin retrogradation, perhaps due to varying extents of residual molecular order in starch materials that are commonly presumed to be fully gelatinized. This article shows that studies of starch retrogradation should take into account the thermal history of the samples even for temperatures above the gelatinization temperature range.