Effect Of Polvdextrose On The Gelatinization And Retrogradation Of Rice Starch

Starch is a widely used and important material in nature,and possesses extensively application in the food industry,but the gelatinized starch is easy to retrogradation under low temperature,restricting the development of starch-based food.Starchhydrocolloids combinitions can effectively delay the retrogradation of starch,improve the quality of food and prolong its shelf lives.The addition of polydextrose make good advantage to improve the fiber content of starch-based food.In this study,taking the high quality water souble fiber polydextrose as object,the main objectives of this work were to study the effect of polydextrose on the gelatinization and retrogradation properties of rice starch;study the structure and properties of modified polydextrose under different pressure dynamic high pressure microfliuidization;then investigate the effect of different modified polydextrose on the gelatinization and retrogradation proterties of rice starch.On the theoretical basis a guiding for the more widespread application of polydextrose in starch-based food and the research of dietary fiber fortified food can be found.First,the effect of polydextrose on the gelatinized viscosity properties,rheological properties,thermal properties,crystalline and microstructure of rice starch was studied.The RVA and DSC results showed that with the addition of polydextrose,the pasting temperature rose,while the gelatinization enthalpy and viscosities decreased,indicating polydextrose delayed the gelatinization of rice starch.At the same time,the breakdown values of RS/PD mixtures decreased significantly,indicating the stability of rice starch improved;the setback values of RS/PD mixtures decreased significantly,which meant that polydextrose could inhibite the short-term retrogradation of rice starch.The static rheological results showed that the RS/PD mixtrues were pseudoplastic fluid,and with the addition of polydextrose,the lag ring area as significantly reduced and the shear stability was enhanced.The strorage modulus of RS/PD mixtrues were much higher than the loss modulus,indicating that the addition of polydextrose influenced the synergistic effect in the elastic properties of the RS/PD mixtrues.The DSC results also showed the retrogradation enthalpy were decreased;and the relative crystallinity of RS/PD mixtrues decreased from 14.09 % to 8.61 %.Meanwhile,SEM results showed that polydextrose could reduce the loss of water,enhance the water retention of rice starch.All above results could be concluded that polydextrose could inhibite the recrystallization of amylopectin and the long-term retrogradation of rice starch.The effect of dynamic high pressure microfluidization treatment under different pressure(80 Mpa,120 Mpa,and 170 Mpa)on the structure and characteristic of polydextrose was investigated.The block structures of polydextrose was destroyed and refined.The molecular weight and average particle size decreased first,then increased,reaching the minimum at 120 Mpa.The apparent viscosity of different polydextrose solution revealed shear thinning with the increase of shear rate.At the same shear rate,comparing with the original polydextrose solution,the apparent viscosity of modified polydextrose solution increased,reaching the maximum at 120 Mpa.There was no new absorption in the FTIR spectrogram of modified polydextrose,the characteristic adsorption peaks presented redshift or blueshift phenomenon in different degrees,indicating the intramolecular and intermolecular hydrogen bond force of polydextrose was abated,water-soluble enhancement.The properties of rice starch with modified polydextrose were investigated by means of RVA,DSC,XRD,FTIR,TPA,and SEM,respectively.RVA results showed the setback values and breakdown values significantly decreased,indicating the modified polydextrose could strengthen the stability and restrain the short-term retrogradation of rice starch.The gelatinization enthalpy of rice starch decreased,and when modified polydextrose at 120 Mpa,the decreasing amplitude was largest,meaning that the delayed effect on the gelatinization of rice starch was more significant.Compared with the addition of original polydextrose,the retrogradation enthalpy and relative crystallinity of rice starch gel decreased;and with the increase of DHPM treament pressure,the retrogradation enthalpy and relative crystallinity of rice starch gel decreased lowest at 120 Mpa,then changed little higher at 170 Mpa.At the same time,with the addition of modified polydextrose,the peak intensity ratio between characteristic peaks 1047 cm-1 and 1022 cm-1 in the FTIR spectrums and hardness values in the TPA measurement both lower first,then higher.These results made clear that modified polydextrose colud inhibite the retrogradation of rice starch,and DHPM treatment at the pressure of 120 Mpa,the most significant effect.