Effect Of Emulsion On The Anti-retrogradation Of Rice Starch

Rice is an essential food product in our country and basically meets the various nutritional needs of the human body.As the main component of rice,starch has a vital influence on rice quality.The retrogradation of starch is a common phenomenon in the storage process of starch,affecting the quality of most rice products.Therefore,the research on the anti-retrogradation of starch has certain practical significance.In this paper,soybean oil and whey protein isolate were used as raw materials to make oil-in-water emulsions with different particle sizes;the effect of emulsion on the gelatinization and retrogradation characteristics of different rice starches was explored;the emulsion was applied to the cooking process of rice,and the effect of the emulsion on the improvement of rice quality was preliminarily evaluated.The main findings of this study were summarized as follows:(1)The effect of nano-emulsion(d43=0.34 ?m)and macro-emulsion(d43=10.60 ?m)on the gelatinization and retrogradation characteristics of rice starch were compared and analyzed.It was revealed that both emulsions could inhibit the gelatinization and retrogradation of starch,and the inhibitory effect increased with the increase in the emulsion concentration.Microscopic observation and Differential Scanning Calorimetry(DSC)analysis showed that during the heating process,the emulsions of the two particle sizes were demulsified,the spilled oil could form amylose-lipid complexes with starch.Compared with the pure starch,when the emulsions with an oil content of 5 wt% were added,the peak viscosities of the two mixed systems were reduced by 6.00% and 24.63%,respectively,and the final storage modulus was reduced by 25.32% and 83.74%,respectively.Besides,the starch gelatinization enthalpy,starch swelling rate,and amylose dissolution rate were all significantly reduced(P<0.05).When the samples were refrigerated at 4 ?,the gel hardness,water retention,and water mobility of the mixed system were reduced,contributing to a denser microstructure of the gel.When the samples were refrigerated for 14 days,the crystallinity of the two mixed systems with an emulsion oil content of 5 wt% decreased by 4.11% and 4.78%,respectively.As demonstrated by comparing the effects of the two emulsions on starch properties,the nano-emulsion presented a stronger effect on starch.(2)The gelatinization and retrogradation properties of nano-emulsion on low amylose rice starch,medium amylose rice starch,and high amylose rice starch were studied,and the effect of emulsion on starch with different amylose contents was compared and analyzed.Studies revealed that emulsions could affect the gelatinization and retrogradation characteristics of the three starches while the mode of action was different.The effect of the emulsion increased with the increase in amylose content.In the detection of thermal properties,water retention,water mobility,and crystallinity of the samples,the emulsions reduced the detection values of the three starches.In the detection of rheological properties and hardness,the emulsion reduced the final storage modulus and gel hardness of medium amylose and high amylose but increased the final storage modulus and gel hardness of low amylose starch.Besides,the effect of emulsion on the retrogradation enthalpy of amylose and amylopectin was investigated using DSC.The results demonstrated that the emulsion had a significant effect on amylose and amylopectin in the early and late stages of starch retrogradation,respectively.(3)The emulsion was applied to the rice cooking process to determine the effects of adding different concentrations of emulsion on the expansion rate,water absorption,hardness,viscosity,and digestion characteristics of three common rice particles.Moreover,the effect of emulsion on improving the quality of rice was investigated.The results indicated that with the increase in the emulsion concentration,the expansion rate and water absorption rate of the three types of rice first increased and then decreased;the overall swelling rate and water absorption rate were the highest when an emulsion with an oil content of 0.5 wt% was added.During the storage of rice,the emulsion could reduce the hardness of the rice and increase its viscosity,with the best effect under the 0.5 wt% oil phase content of the emulsion.The results of in vitro digestion suggested that the emulsion increased the resistant starch of three kinds of rice,lowered the hydrolysis index of the rice and assessed the glycemic index,and inhibited the digestion of the rice.