| The purpose of this paper is to use transglutaminase(TG)to catalyze grain protein and interact with rice starch to form a blend system.The effects of proteins before and after TG enzyme catalyzed on the functional properties such as thermal properties,gelatinization properties and structure and digestibility of rice starch were studied and their interactions were preliminarily explored.Firstly,this paper explored the compound conditions of rice protein(RP)before and after TG enzyme catalysis on rice starch,and preliminarily explored the mechanism of protein under TG enzyme catalysis interaction with starch in the hydrothermal process.Using infrared spectroscopy and in vitro digestibility as the measurement indicators,based on the single factor results,the orthogonal experiment was carried out to optimize the optimal process parameters of effect of TG enzyme catalyzing RP on rice starch,that is:the reaction temperature is 50℃,the amount of rice protein added is 10%,and the amount of TG enzyme is 4.5 U/g.The verification test was carried out on the optimum process conditions obtained,and the results showed that the rapidly digestible starch(RDS)content of RS under this condition was 74.14%,that is,the digestibility of RS was reduced the most.The results also showed that TG enzyme had no significant effect on starch digestibility,the reduction degree of starch digestibility will increase with the increase of protein addition,the participation of TG enzyme can make the reduction effect of starch digestibility more significant through catalytic modification of protein.The results of observing the apparent morphology of the samples by polarizing microscope showed that the protein under the catalysis of TG enzyme made the structure between starch particles more dense and aggregated.Secondly,the effects of different amounts of cereal protein before and after TG enzyme catalysis,namely rice protein(RP),corn protein(CP)and wheat protein(WP),on the functional properties of starch expansion coefficient and solubility,amylose overflow rate,particle size,thermodynamic properties and gelatinization properties were studied and compared under the condition of process optimization.The results showed that compared with natural starch,starch-enzyme blend system had no significant effect on the functional properties of starch,while the proteins TG enzyme catalysis had a significant effect on the functional properties of starch.(1)Compared with the starch-natural protein blend system,in the starch-protein-enzyme blend system,the interaction between protein catalyzed by TG enzyme and starch was further enhanced,and the starch expansion coefficient and amylose overflow rate continued to decrease with the increase of protein addition,and the influence degree of three cereal proteins was RP>CP>WP.(2)The results of particle size showed that compared with natural starch,the increase of starch particle size in all samples is related to the role and amount of protein,and the effect of WP was more significant;Compared with the starch-natural protein blend system,the protein catalyzed by TG enzyme showed a relatively decreasing trend on the particle size of starch.(3)Differential scanning calorimetry(DSC)results showed that the three cereal proteins before and after TG enzyme catalysis had no significant effect on the thermal properties of starch,the gelatinization onset temperature and peak temperature increased less,and the gelatinization enthalpy decreased in varying degrees.(4)The test results of rapid viscosity analyzer(RVA)show that in the starch system,the participation of TG enzyme can catalyze protein to have a more significant impact on the gelatinization characteristics of rice starch.Grain protein can significantly increase the gelatinization starting temperature of starch and reduce the gelatinization parameters such as peak viscosity,final viscosity and retrogradation value of starch.Finally,the effects of three cereal proteins before and after TG enzyme catalysis on short-range ordered structure,crystalline structure,the digestibility,static rheological properties and particle morphology of rice starch were studied and compared.The results also showed that starch-enzyme blend system had no significant effect on the structure and rheological properties of starch,and the effect of grain protein before and after TG enzyme catalysis was related to the type of protein and its addition level.(1)The results of infrared structural characteristics and X-ray diffraction showed that cereal protein could enhance the short-range ordered structure and crystallinity of starch in varying degrees.The protein under the catalysis of enzyme could significantly enhance the short-range ordered structure of starch,so that the starch had higher crystallinity and more ordered type a structure.(2)The results of in vitro digestion showed that the participation of TG enzyme in the system could better reduce the digestibility of starch by catalyzing the modified protein.The effects of the three proteins were as follows:WP>CP>RP.(3)The static rheological results showed that the participation of TG enzyme could catalyze protein to effectively reduce the viscosity of rice starch,among which the viscosity of starch-10%RP-enzyme,starch-15%CP-enzyme and starch-10%WP-enzyme samples decreased more significantly.(4)The results of scanning electron microscope showed that the protein before and after TG enzyme catalysis changed the morphology of starch particles from smooth and loose structure to dense microporous network structure;With the increase of protein content,the volume of starch granules increased slightly and the morphology continued to be clear;In the interaction system of TG enzyme catalyzed protein and starch,the starch granules are partially fused and the granule structure is gradually curved from polygonal edges. |
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