The Effect Of Ultra-high Pressure Treatment On The Preparation Of Slowly Digestible Starch Of Glutinous Rice By Temperature-cycled Retrogradation

In the experiment,glutinous rice flour which protein content is about 7.97%and glutinous rice starch which protein content is about 0.58%are used for ultra-high pressure treatments of 0,100,300 and 500MPa respectively.And the samples are processed at a time interval of 24h and was placed for 7 days under the retrogradation process of 4?and 25?circulating temperature environment.This study focus on the slowly digestion starch content and exploring properties of the glutinous rice powder and starch groups.1)The slowly digestion starch content of the glutinous rice flour group did not change much during 7 days,but increased slightly with the increase of storage time.The slowly digestion starch content of the glutinous rice starch group increased with the increase of the storage days and ultra-high pressure.When the ultra-high pressure is500MPa and the storage days are 7 days,the content of slowly digested starch produced by the glutinous rice starch group can reach up to the highest which is30.32%.2)Thermodynamic properties results showed that the enthalpy changes of the melting peaks of the glutinous rice powder group and the glutinous rice starch group both increased with the increase of storage time.The enthalpy change of the glutinous rice powder group was significantly greater than the enthalpy change of the glutinous rice starch group.The slowly digestible starch content of the glutinous rice powder group and the glutinous rice starch group both increased with the increase of storage time.Because the glutinous rice powder group contained protein that interacts with starch,the speed and degree of aging retrogradation were weaker than that of the glutinous rice starch group.The number of ordered structures is less than that of the glutinous rice starch group,so the ratio of slowly digestible starch in the glutinous rice starch group is higher than that of the glutinous rice powder group.3)Gelatinization test results illustrated that the final viscosity of the powder group increased with the increase of the processing pressure,but the rebound value did not change much.While the increased with the processing pressure,the rebound value and finally viscosity of starch group decrease.The rebound value and final viscosity of the starch group were greater than those of the powder group.The greater the ultra high pressure,the more covalent bonds between starch molecules,between starch molecules and proteins and lipids can be opened.The greater the surface area exposed to starch molecules,the more likely it is to recrystallize and form slow digestion during the retrogradation process.So if the regeneration time is sufficient,when the pressure is higher,the slowly digestion starch content of the sample is higher.4)FTIR results displayed that the peak positions of the powder and starch group are basically the same,but the powder group has a characteristic peak-NH₂ at 1560cm^-1.Fourier transform infrared spectroscopy was de-convoluted to study the degree of short-range sequence changes caused by hydrogen bond formation.It was found that with the increase of storage time,the ratio of powder group at 1047 cm^-1/1022 cm^-1did not change significantly,while the ratio of starch group gradually increased.The LF-NMR results showed that the A₂₁ value of the powder group was greater than that of starch group,and the A₂₂ value of the starch group was greater than that of the powder group.And with the increase of storage time,the A₂₁ value of the two groups showed a trend of firstly increasing and then decreasing while the A₂₂ trend firstly decreasing and then increasing.These results are consistent with the conclusions of thermodynamic experiments and gelatinization experiments.