Effects Of Low Temperature On Retrogradation Of Waxy Rice Starch Gel

Starch is the major food source and important components of all kinds of plants in nature.Retrogradation of starch is still a bottleneck which restricts the development of food.Cooling rate and storage temperature have significant effects on the starch retrogradation.Freezing and frozen storage can effect sample quality and inhibited waxy rice starch retrogradation,however,the rertogradaion of starch gel precooling with low and ultra-low temperatures has not been studied in detail.Therefore,the effects of low(-20,-40℃)and ultralow temperature(-195℃)precooling on the retrogradation,crystalline structures and texture properties of waxy rice starch gel and the complex of starch were studied by Differential Scanning Calorimeter(DSC),X-ray Diffraction(XRD)and Texture Profile Analysis(TPA).Waxy rice starch granule was mostly irregular polygon,angular and smooth surface of polyhedron,particle size was smaller and the crystal type is A-type with the crystallinity of31.04%.Its amylose content was 1.41%.The temperature of gelatinization was from 74 to86℃.The enthalpy of waxy rice was 3.5657J/g.The endothermic peak of “typeⅡa”starch-lipid complexes was formed.The dissociation peak of starch-lipid complexes was109.9℃with the heat enthalpy of 0.0459J/g.The diffraction peaks at 19.5°was observed which indicative of formation of V-type amylopectin-lipid complex.The addition of lauric acid reduced the waxy rice starch breakdown values and retrogradation value,improved the stability of the waxy rice starch gel structure,inhibited waxy rice starch retrogradation.The retrogradation enthalpy of waxy rice starch gel with low temperature,ultra-low temperature and non-precooling were 0.1955,0.2057,0.1277 and 0.8765J/g;the crystallinity were 6.05%,3.83%,5.36% and 7.38%;the changes of the hardness values were 875.54,875.54,739.27 and 1074.87 g respectively stored 21 days at 4℃;these results indicated that precooling can inhibit waxy rice starch gel retrogradation,and ultralow-temperature freezing can effectively inhibition waxy rice gel retrogradation during storage.The retrogradation enthalpy value,crystallinity and hardness of precooling waxy rice starch gel was increased rapidly from1-7days,increased from 7-14 days,changed slowly from 14-21 days and reached the highest during chill storage.Precooling with low temperature,ultra-low temperature had no significant effect on retrogradation enthalpy value,crystallinity,hardness and spring of waxy rice starch gel during frozen storage.The retrogradation enthalpy value and crystallinity of starch-lauric acid complex precooling with low temperature and ultra-low temperature were investigated by DSC and XRD.The retrogradation enthalpy value and crystallinity of Starch-lauric acid complex increased rapidly from 1-7days,increased slowly from 7-21 days,last reached the maximum in 21 days during chill storage.which the retrogradation enthalpy value were 0.0806J/g(-20℃),0.0889J/g(-40℃)and 0.0540J/g(-195℃),the crystallinity were 3.82%,3.75% and 3.08%,respectively.However,the retrogradation enthalpy value and crystallinity of non-precooling starch-lauric acid complex were 0.2841J/g and 5.22%.Precooling can inhibit starch-lauric acid complex retrogradation,the ultra-low temperature was more significant inhibition.Hardness of precooling starch-lauric acid complex was not significant increased within 1day,increased rapidly from 1-7 days,increased slowly from 7-14 days,finally reached the maximum(714.77,653.5 and 557.97g)in 21 days.Precooling with low temperature,ultra-low temperature had no significant effect on retrogradation enthalpy value,crystallinity,hardness and spring of waxy rice starch gel and starch-lauric acid complex during frozen storage.