Effects of Ultra-high Pressure Treatment on the Preparation of Slowly Digestible Starch from Glutinous Rice by Temperature-Cycled Retrogradation

Slowly digestible starch (SDS) was prepared separately from glutinous rice flour (with 7.97% protein) and glutinous rice starch (with 0.58% protein) by ultra-high pressure (100, 300 and 500 MPa) combined with temperature-cycled retrogradation (holding at alternating temperatures of 4 and 25 ℃ for 1, 3 and 7 days with 24 h intervals). The influence of ultra-high pressure (UHP) treatment on the purity, thermal properties, gelatinization properties and Fourier transform infrared (FTIR) spectrum of SDS was evaluated. The experimental results showed that the purity of SDS prepared from glutinous rice starch was higher than that prepared from glutinous rice flour. After 7 days of temperature-cycled retrogradation, the purity of SDS prepared from glutinous rice starch with UHP treatment at 500 MPa reached a maximum level of 30.32%. The differential scanning calorimetric (DSC) experiments showed that the enthalpy change of the SDS samples increases after temperature-cycled crystallization. The rapid viscoanalyzer (RVA) experiments demonstrated that the retrogradation value and final viscosity of SDS from glutinous rice starch decreased and the purity increased with increasing pressure. The FTIR spectra illustrated that the proportion of short-range ordered structure in SDS from glutinous rice starch was higher than that from glutinous rice flour.