Effect of high hydrostatic pressure (HHP) on slowly digestible properties of rice starches

The slowly digestible properties of high hydrostatic pressure (HHP)-gelatinized non-waxy and waxy rice starches during the retrogradation were evaluated in this study. The results show that slowly digestible starch (SDS) was observed at a higher percentage in HHP-gelatinized, non-waxy and waxy rice starches than in heat-gelatinized starches, after retrogradation for 7 days. The HHP treatment significantly reduced the enthalpy change of starch retrogradation and retarded the freezable water transformation into unfreezable water during retrogradation. This indicated that the SDS percentage was not positively correlated to the retrogradation degree of starch. Furthermore, X-ray diffraction (XRD) data revealed that the HHP treatment decreased the perfect crystallites of the 7 day-retrograded. Non-waxy and waxy starches from 19.5% to 12.1% and 15.7% to 11.4%, while increased imperfect crystallites from 26.4% to 30.7% and 28.6% to 31.3%, respectively. These findings suggest that the higher SDS percentage can be attributed to the formation of less perfect crystallites and more imperfect crystallites during the HHP and retrogradation treatments.