Mechanistic studies of starch retrogradation and its effects on starch gel properties

The influence of residual short-range molecular order on the mechanism of starch retrogradation was examined by measuring functional properties of retrograding starch gels that were prepared by heating starch with different amounts of water at 100 °C. Analyses using X-ray diffraction (XRD), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and laser confocal micro-Raman (LCM-Raman) spectroscopy showed that as short-range molecular range in the gelatinized starch decreased, so did long- and short-range molecular order, gel firmness, water mobility and susceptibility to in vitro enzymic digestion of the corresponding starch as it retrograded over time periods ranging from one to 21 days. The rate and extent of these changes were controlled by the amount of residual short-range molecular order in the starch after gelatinization, which in turn, was a function of the amount of water used for gelatinization. Starch gelatinized with 50–70% water formed had residual short-range molecular order and retrograded more quickly to form stronger gels, whereas starch gelatinized with 75 and 80% retained little structural order and retrograded more slowly, forming softer gels in which the starch crystallites were better-defined. Our study provides new insights into the mechanism of starch retrogradation and its effects on functional properties of retrograded starch gels, which is likely to be of interest for starch in foods and other applications.