| In recent years,with the improvement of living standards and the increasing variety of diseases,more and more people prefer nutritious and healthy as well as fashionable cereal food.3D printing technology(3DP)undoubtedly provides a new way to realize the personalized customization of healthy cereal food due to its intelligent,personalized,green and environmental characteristics,as well as it can meet the needs of different groups of people on food quality,nutritional function and modeling.In this paper,the relationship between the multi-scale structure,rheological properties and the printability of starch,the main component of cereal food,was systematically studied to provide theoretical basis and basic data for the application of hot-extrusion 3D printing(HE-3DP)in the manufacturing of starch and healthy cereal food,based on the current situation and problems of application of hot extrusion 3D printing technology in terms of grain food,as well as the key role that the rheological properties of printing materials play in the shaping during HE-3DP.In this paper,the rheometer was used to simulate the HE-3DP process to explore the rheological properties of rice starch,potato starch and corn starch during HE-3DP.In addition,the printability of each starch was studied to establish the relationship between starch rheological properties and printing behaviors.Thus,the reasonable prediction method of printing process parameters was obtained.Based on these,modern analytical techniques were used to further reveal the effects of HE-3DP on the multi-scale structure,rheological properties and printability of starch at different printing temperatures and starch concentrations,meanwhile,as well as establish the mutual control relationship among the three parts.The details and main conclusions are shown in the following.The rheological properties and printability of rice starch,potato starch and corn starch were systematically investigated.It was found that each starch showed a shear-thinning behavior,as well as the feature of a substantial decrease at higher strains and a recovery at lower strains in storage modulus.Besides,the flow stress(?_f),yield stress(?_y),and G'exhibited increase first and then decrease as the temperature increasing,and obviously increase with raising the concentration.Rice starch at 15-25%,corn starch at 20-25%,and potato starch at 15-20%displayed preferable printing behavior.Among the three kinds of starches,rice starch showed more prominent printing behavior,with the number of printing layers up to 43-60 and the line width of 0.80-0.97mm,which is more suitable for HE-3DP.The printing behavior of starch material show high agreement with the rheological results,starch materials with?_f(140-722 Pa),?_y(32-455 Pa)and G'(951-5074 Pa)possess favorable printing behaviors.Therefore,HE-3DP performance of starch materials can be predicted and regulated by G',?_f and?_y.The effects of HE-3DP on the multi-scale structure,rheological properties and printability of starch at different printing temperatures and starch concentrations were explored,it was revealed that the short-range ordered molecular structure of starch was damaged with the increase of printing temperature.The original crystal structure of corn starch,potato starch and rice starch were completely destroyed after printing and all showed the characteristics of amorphous structure,however,rice starch formed V-type crystallite with single helix structure and partial ordered structure.It was found that the porous gel network structure of the printed samples become compact with the increase of starch concentration,the gel system formed by the printed corn starch and potato starch were relatively uniform,while the inhomogeneity of microstructure was found in printed rice starch on submicrostructure scale.In addition,as the printing temperature increased,the printed starch gradually transformed into porous network structure,however,neither low nor high printing temperatures were conducive to the formation of starch gel network with uniform and good stereoscopic appearance.The dynamic rheological results of the printed starch samples were consistent with the changes in the in situ test results on the rheometer.G',?_y and?_f increased with the increase of starch concentration,and increased first and then decreased with the increase of printing temperature.It was revealed that the printed starch gel network was more compact due to higher starch concentration,thus the mechanical strength of the gel system imparted to itself was higher,and however,it made it difficult for the starch samples to be extruded from the fine nozzle since?_f also increased with increasing concentration.Additionally,the gel structure strength of the printed starch samples first increased and then decreased as the printing temperature increased,corn starch,potato starch and rice starch printed at 70?,70?and 80?separately,holding higher G'and?_y values than printed at other temperatures,thus the formed gel network had better structural integrity and higher strength to get more ideal printability.In summary,this work involved systematic investigation of the relationship between the rheological properties and 3D printing behaviors of starch and ascertained the prediction method for determining reasonable printing parameters.Furthermore,the relationship among starch multi-scale structure,rheological properties and printability at different printing temperatures and starch concentrations was revealed from the view of hierarchical structural changes at molecular level.The research results provide a new idea and method for the application of HE-3DP technology in the manufacture of starchy cereal food,as well as the physical modification of starch,demonstrated profound scientific significance and practical value. |
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