Comparative study of the retrogradation of intermediate water content waxy maize, wheat, and potato starches

The retrogradation of extruded starches from three different botanical sources was studied in concentrated conditions (34 +/- 1% water) at 25 degreesC using differential scanning calorimetry (DSC) and isothermal calorimetry, Fourier transform infrared spectroscopy (FTIR), and wide-angle X-ray scattering. Potato starch showed the highest rate of retrogradation (similar to0.17 h(-1)) followed by waxy maize (similar to0.12 h(-1)), while the retrogradation of wheat starch was the slowest (similar to0.05 h(-1)). In addition to the kinetics, the extent of molecular order in the retrograded samples was studied in detail in terms of short-range (helical) and long-range (crystalline) distance scales. The amylopectin crystallinity indices were essentially the same (similar to47-51% amylopectin basis) for the three starches. However, significant differences were found in the enthalpy of melting measured by DSC after full retrogradation (potato, 11.6 +/- 0.7; waxy maize, 9.0 +/- 0.5; and wheat, 6.1 +/- 0.3 J/g of amylopectin). The degree of short-range molecular order in the retrograded state determined by FTIR was waxy maize > potato > wheat. The effect of amylopectin average chain length and the polymorphism of the crystalline phase were taken into account to explain the differences in the retrogradation enthalpies.