Research On Low Temperature Anti-retrogradation Agent Of Rice Flour And Its Effect On The Starch Properties

The consumption of rice and its relevant products is huge every year.However,it is easy to retrogradation during storage and leads to decrease quality and short shelf life because of the high starch content.Although the current technology of anti-retrogradation can retard the deterioration of quality,the problem of retrogradation in rice products at low temperature storage is still exist.The current technology can not achieve the target of controlling quality,and the internal mechanism of anti-retrogradation in low-temperature storage is not perfect.Therefore,this experiment synergistically added both additives and enzyme to achieve the purpose of retarding the retrogradation of starch,and explored the effect on starch properties in order to provide theoretical support for the improvement of quality and the extension of shelf life of rice products at low temperature.In this study,we respectively contrasted and researched the effect of three kinds of emulsifiers(0.3% sucrose ester,0.2% stearic acid sodium lactate(SSL)and 0.2% monoglyceride(GMS)),three kinds of hydrophilic colloids(0.15% xanthan gum,0.1% guar gum and 0.1% sodium alginate)and two kinds of additives(0.15% ?-cyclodextrin and 0.3% konjac glycoside(KGM))on the textural properties,retrogradation properties and water content of rice flour at low temperature.The 0.2% GMS sample had the best hardness,adhesiveness and retrogradation index at 4°C and-20°C in the emulsifier,and the water content of the 0.2% GMS was the highest at 4°C,which inhibited the increase of hardness and retrogradationindex(?Hr/?Hg)of rice flour in the retrogradation stage.Although 0.15% xanthan gum can not control the water content well,the effect on the texture and retrogradation index of rice flour was the most obvious in the hydrophilic colloid.The retrogradationindex,water content(4°C and-20°C)and the hardness and adhesiveness(-20°C)of the 0.15% ?-cyclodextrin sample were better than 0.3% konjac glucoside.Therefore,we choosed 0.2% GMS,0.15% xanthan gum and 0.15% ?-cyclodextrin as the suitable anti-retrogradation factors.In addition,low temperature storage was conducive to food preservation,the temperature in-20°C could extended shelf life of rice flour more than 15 d compared with 4°C.Three anti-retrogradation factors were combined by gradient experiment and response surface method.Basing on this,we used ?-amylase,?-amylase and xylanase to further optimize the anti-retrogradation conditions.Finally,we made sure that the technological process of low temperature anti-retrogradation agent was: 0.22% GMS,0.16% xanthan gum and 0.19% ?-cyclodextrin,fully mixed with rice flour,water was added to obtain a ratio of 1:2(rice/water;w/v),and then enzymed with ?-amylase,the concentration of enzyme was 30 U/g,the enzyme action temperature was 60°C,the enzyme action time was 40 min,the enzyme action p H was 6.5,finally samples were immersed in a 90°C hot bath for 30 min,which became rice gels.Rice products obtained by this technological process,which can keep good quality,the retrogradation index,rheological properties and water activity were maintained well storing at 4°C for 13 d with a significant inhibition of starch retrogradation.A sample without addition of rice was used as the control.We used the method of X-ray diffraction(XRD),scanning electron microscopy(SEM)and differential scanning calorimetry(DSC)to analysis crystallinity,particle morphology and retrogradation characteristics of amylose and amylopectin sampleswith low temperature anti-retrogradation agent.X-ray diffraction patterns showed that samples with low temperature anti-retrogradation agent reduced the intensity of 17° characteristic diffraction peak and the half width of spike,and the low temperature anti-retrogradation agent could delay the transformation of crystal type,reduced starch granules,retarded the retrogradation of rice products compared with control group.The scanning electron microscopy showed that the volume of the starch granules increased with the storage time,the surface was sunken and the size was not uniform,but the overall volume change of starch granules after treatment with low temperature anti-retrogradation agent was not obvious,the local small particles had adhesions and the whole distribution was uniform,which indicated that low temperature anti-retrogradation agent inhibited the agglomeration of starch granules,reduced the hardness and increased water content of rice products,delayed the retrogradation of the gelatinized rice flour.Meanwhile the addition of low temperature anti-retrogradation agent also reduced the enthalpy(?Hr)of amylose and amylopectin,after storing at 4°C for 20 d,which reduced the enthalpy of amylose by 31% compared with the control,and reduced the enthalpy of amylopectin by 40%.The result illustrated that the anti-retrogradation effect of amylopectin was better than amylose.