Effects of moisture content and different gelatinization heating temperatures on retrogradation of waxy-type maize starches

The effect of moisture content on retrogradation of wx, du wx, ae wx, and su2 wx maize starches was studied by differential scanning calorimetry (DSC). All starches showed maximum retrogradation enthalpy at an intermediate moisture content, but the precise relationship between moisture content and retrogradation enthalpy varied for each starch. The ae wx starch was least affected by moisture content, showing measurable retrogradation (2–3 J/g) after only 1 day for the 95% moisture sample. Retrogradation of the su2 wx starch was exceptionally slow even at intermediate moisture contents, and the retrogradation enthalpy was particularly sensitive to moisture content. The effect of varied moisture content was also investigated in combination with initial heating to a wide range of temperatures. Retrogradation of wx, du wx, and su2 wx starches, but not ae wx starch, was strongly influenced by both initial heating temperature and moisture content, with development of enthalpy consistently in the order of du wx>wx>su2 wx. The chain length profiles for the four starches were unique. The exceptionally rapid retrogradation and relatively small concentration dependence of ae wx starch may be related to a greater proportion of longer chains, whereas the very slow retrogradation of su2 wx starch may be related to a population of exceptionally short chains. The more rapid retrogradation of du wx starch than wx starch may be related to the high number and concentration of branch points in a cluster.