| Starch as a renewable resource,has a wide range of research value and application prospects,and Lipu taro is rich in starch,with high digestibility,eating too much is easy to lead to high human blood sugar level,is not conducive to maintaining human blood sugar balance.In this paper,Liyu taro was used as raw material,xylanase and neutral protease were selected to improve the extraction rate of taro starch,and citric acid was assisted by ultrasonic esterification modification to improve the anti-enzymatic performance of starch,so as to explore the microstructure and in vitro digestion characteristics of starch citrate ester,and the esterified starch raw material was applied to noodles,providing certain technical reference for the development of GI food.The extraction technology of taro starch was optimized by single factor test and response surface method,and the physicochemical properties and processing characteristics of starch were determined.The results showed as follows:1)The optimal technology of double enzyme extraction of taro starch was as follows:double enzyme ratio（xylanase:neutral protease）was 2.6,total enzyme amount was 2.14%,hydrolysis time was 4.4h,hydrolysis temperature was 56℃,hydrolysis p H was 6,and the yield of taro starch was 90.6%.2)The contents of protein and amylopectin of taro starch extracted by double enzymes decreased by 1.57%and 2.56%,the transparency,swelling rate and freeze-thaw stability increased by 2.09%,1.13%and 2.33%,and the solubility decreased by 1.93%,and the processing characteristics of two kinds of starch extracted by double enzymes significantly changed.The wet preparation technology of CTSE was optimized by single factor test and response surface method.The microstructure and characterization of CTSE were analyzed by scanning electron microscopy,X-ray diffraction and Fourier infrared spectroscopy.The processing characteristics and in vitro digestion characteristics of CTSE were simulated by differential scanning calorimeter,rheometer and in vitro digestion.The results showed as follows:1)The optimum process of wet CTSE preparation was as follows:ultrasonic power 480 W,citric acid content 44%,ultrasonic time 92 min,treatment temperature 68℃,CTSE substitution degree0.1847.2)Under scanning electron microscope,the modified starch showed obvious cluster phenomenon,and the particle size was smaller,the surface was rough,and there was depression;By X-ray diffractometer,the crystal structure is still A-type,but the relative crystallinity decreases by 13.71%.By Fourier infrared spectroscopy analysis,it is found that a new absorption peak appears at the wavelength of 1597cm-1which is vibrated by the C=O bond.Thermodynamic analysis showed that T0,Tp,Te andΔH were significantly greater than that of taro starch,and the thermal stability was improved.3)The rheological properties of taro starch before and after modification can be measured.The results show that the modified taro starch paste can achieve the same shear rate,the shear stress required decreases,the hysteretic ring area decreases significantly,and the rheological properties of starch paste system increases.4)The in vitro digestion and kinetic analysis before and after CTSE were simulated,and it was found that the content of resistant starch（RS）was significantly increased compared with the original starch,and the content of RS was proportional to the degree of substitution of CTSE.The hydrolysis curve was fitted by the kinetic equation,and the glycemic index（GI）of CSTE was 45.79<55,which was a low GI food.The preparation process of CTSE noodles was optimized by orthogonal method.The flour,texture,cooking and glycemic index of CTSE noodles were analyzed by electronic powder analyzer,texture analyzer and simulated in vitro digestion.The results showed as follows:1)The preparation process of CTSE noodles:the amount of CTSE added was 20%,the amount of water added was 55%,the kneading time was 18 min,the amount of salt added was 4%and the sensory score of the noodles was 90.5;The addition of CTSE changed the silty properties of dough to a certain extent.The water absorption,formation time and stabilization time of dough showed a decreasing trend with the addition of CTSE,while the weakening degree showed an increasing trend.2)The hardness and elasticity of noodles showed a decreasing trend with the addition of CTSE,while the chewability,adhesion and resilience of noodles showed an increasing trend.3)The cooking characteristics of CTSE noodles decreased significantly with the addition of CTSE.The optimal cooking time,noodle loss rate and strip breaking rate showed an increasing trend,while the water absorption showed a decreasing trend.4)The addition of CTSE to noodles can significantly reduce the digestion rate of noodles.After calculation,the glycemic index（GI）of noodles is proportional to the amount of CTSE added.After optimization,the GI of CTSE noodles is 63.98<70,which belongs to the middle GI food.Conclusion:The combination of xylanase and neutral protease can significantly improve the extraction yield of taro starch.Compared with conventional water extraction method,the processing characteristics of starch extracted by double enzyme method are significantly improved.After ultrasonic citric acid modification of taro starch,the particles of taro starch became smaller,the crystallinity of taro starch decreased,the thermal stability increased,the RS content of CTSE was significantly increased,showing good anti-enzymatic performance.Its application in noodle production can significantly reduce the GI of noodles,thus reducing the blood sugar level of the human body,which provides certain theoretical support for the development of GI food. |
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