| 3D printing technology is an emerging food processing technology in recent years,with typical digital and intelligent features,playing an important role in the field of food additive manufacturing.Currently,the raw materials used for food 3D printing include chocolate,cheese and starch gels.Most of the starch gels have the problem of low printing accuracy,which limits their potential application in the field of food 3D printing.Cassava starch is widely used in the food industry and is also one of the important industrial raw materials.Current research on the 3D printing of starch gels mainly focuses on the relationship between the rheological properties of starch gels and 3D printing accuracy.However,the multi-scale structure of starch,especially the fine structure,is the material basis for determining the gel properties and 3D printing accuracy,and the reason how the multi-scale structure of starch regulates its gel properties and printing accuracy in different food systems is still unclear,and the related research is relatively scarce.In view of this,this paper firstly investigated 3D printing applicability of cassava starch gels and clarified the structure-activity relationship between the fine structure of the original starch and the quality of the printed products;then,on the basis of the finding that the printing accuracy of cassava starch gels was poorer,it explained from the perspective of the starch multi-scale structure and gel properties that the proteins and fatty acids enhanced the printing accuracy of cassava starch gels in the binary gel system,respectively;then,the key to improve the printing accuracy of cassava starch-based ternary gel system was explored;finally,4D-printed bakery products with programmed deformation characteristics were developed based on the above ternary gel system.The results of the study can provide new ideas for the development and creation of new starch-based 3D printing products,which is of great socio-economic significance for promoting the high-value processing and utilization of cassava starch.The main research contents and results are as follows:1.Study on the 3D printing applicability of cassava starch gelCassava starch was used as a raw material to explore the difference in 3D printing quality between its gels and those of potato starch,sweet potato starch,corn starch,wheat starch,and buckwheat starch,to clarify the structure-activity relationship between the fine structure of the original starch and the 3D printing quality of the gel,and to reveal the reasons for the differentiation from the perspective of the fine structure of the original starch.In the original starch,the low percentage of 36<X≤100amylopectin（AP）chains,the high percentage of 13<X≤24 AP chains,and the high percentage of 5000<X≤20000 amylose（AM）chains were favorable to enhance the fluidity of the ink,which allowed the ink to be extruded from the nozzle smoothly.The low average molecular size（（?）h）and high proportion of 100<X≤1000 AM chains in the raw starch were favorable for enhancing the printing accuracy of 3D printed products.The higher（?）h and lower proportion of 100<X≤1000 AM chains in cassava starch were the main reasons for its lower gel printing accuracy than that of corn starch,wheat starch and buckwheat starch gels.2.Investigation of protein enhancement of the 3D printing accuracy of cassava starch gelTaking cassava starch as raw material,the effect of protein on the 3D printing accuracy of cassava starch gel was investigated.Firstly,the types of proteins were screened,and the results showed that casein protein had the best effect on enhancing the printing accuracy of cassava starch gel,and then the reasons for casein protein to enhance the printing accuracy of cassava starch gel were explored.The results showed that the printing accuracy of cassava starch gel increased from 82.73%to 92.27%as the casein protein addition increased from 0%to 10%.The addition of casein protein could increase the （?）h of starch after thermo-gelatinization,which reduced the extruded line width during the printing process and increased the center height of the printed product,resulting in improved precision of the printed product.In addition,the addition of casein protein inhibited the retrogradation of cassava starch gels and reduced the short-range order of the starch,which led to an increase in the free water(A23)content of the gel system and resulted in an increase in the elastic modulus（G′）of the gel,thus improving the self-supporting property of the printed products and the printing accuracy.3.Investigation of lipids enhancement of the 3D printing accuracy of cassava starch gelTaking cassava starch as raw material,the effect of fatty acids on the printing accuracy of cassava starch gel was investigated.Firstly,the change rule of fatty acid content affecting the printing accuracy of cassava starch gel was explored,and then the reasons why fatty acids with different chain lengths and unsaturation degrees enhanced the printing accuracy of cassava starch gel were explored.The results showed that the printing accuracy of cassava starch gel exhibited a tendency of first increasing and then decreasing with the increase of lauric acid content.In addition,a decrease in fatty acid chain length and an increase in the degree of unsaturation enhanced the printing accuracy of cassava starch gels.Lauric acid,which has the shortest carbon chain length,and linolenic acid,which has the largest degree of unsaturation,improved the printing accuracy of cassava starch gel most significantly.The reduction of fatty acid carbon chain length not only increased the （?）h of the starch after thermo-gelatinization,but also reduced the proportion of AP chains with 6<X≤12 in the starch and elevated the crystallinity of the starch,in which the shorter carbon chains of lauric acid formed the V-shape structure with the starch.These multi-scale structural changes benefitted the elastic modulus of the gel system,resulting in high support of the printed product and improved printing accuracy.The increase in the degree of fatty acid unsaturation increased the （?）h and the ratio of 100<X≤1000 AM chains of starch,reduced the degree of depolymerization of starch molecular chains,thus improving the modulus of elasticity of the gel system,and ultimately enhanced self-supporting properties of the printed products and printing accuracy.4.Investigation of 3D printing accuracy improvement of cassava starch-based ternary gel systemIn the more complex ternary system,the effects of protein and fatty acid types on the 3D printing accuracy of the gel system were first explored.Based on the discovery that proteins enhance the accuracy of ternary gel system more,the influence of protein structure on the ink extrusion process was clarified by combining computational fluid dynamics（CFD）,and then the influence of protein structure on the printing accuracy of cassava starch-based ternary gel system was revealed from the perspective of the multi-scale structure and gel properties of starch.The results showed that the high content ofα-helix and low content of irregular curl in the proteins were favorable to the printing accuracy of the ternary gel system.The high content ofα-helices in proteins enhanced the shear rate of the ternary gel system at the nozzle,which was conducive to the smooth extrusion of the gel in the 3D printing process.The high content ofα-helices also reduced the speed of gel movement in all directions at the nozzle,thus reducing the extrusion expansion of the filament and smoothing the surface of the filament.In addition,the high content ofα-helices and the low content of irregular curls in proteins increased the number of V-crystalline structures,（?）h and the proportion of AM chains with 100<X≤1000 of starch in the ternary gel system,and decreased the proportion of AP chains with 6<X≤12 in starch,and these multi-scale structural changes resulted in the increase of the A23 content in the ternary gel system,which made the elastic modulus of the gel system increase,thereby increasing the mechanical properties of the 3D printed products and ultimately enhancing the printing accuracy of the printed products.5.Study on 4D printing programmed deformation of cassava starch-based ternary gel systemBased on the above ternary gel system,a double-layer structure of hydrogel was designed to explore the influence of baking temperature,nozzle size,internal structural parameters such as printing path and filling rate,as well as the material composition on the degree of deformation of 3D printed products,and the special deformation behaviors of the printed products were studied through the design of the complex model and the control of internal parameter conditions.The results showed that the deformation degree of the printed products was minimized when the printing path of the second layer of the double-layer structured hydrogel was perpendicular to the first layer,and the deformation effect of the printed products was optimal when the printing path of the second layer was the same as that of the first layer.Decreasing the syringe nozzle diameter and increasing the aspect ratio of the printed product could enhance the deformation effect of the product,while the increase in the filling rate would cause the final deformation angle of the printed product to show a tendency of first increasing and then decreasing.The increase in baking temperature led to rapid dehydration of the 3D printed products in a short period of time,and its skeleton rapidly transformed from the elastic state to the glassy state,which led to a large degree of deformation of the printed products in the early stage.However,the rapid transformation of the skeleton state led to the hardening of the surface of the 3D printed product,which affected the degree of subsequent deformation,resulting in a lower degree of final deformation of the printed product.In addition,the addition of butter reduced the final bending angle of the printed product,while the addition of white granulated sugar enhanced the final bending angle of the printed product.Finally,special deformation behaviors of cassava starch-based baked goods were achieved by adjusting parameters such as filling rate,printing path and nozzle size,such as automatic"wrapping"of flat boxes and petals,as well as automatic"curling"of octopus tentacles and other behaviors during the baking process.In summary,this study improved the printing accuracy of cassava starch gel through the construction of cassava starch composite gel system,developed controllable deformation of cassava baked food,which provided new methods and ideas for the high-value processing and utilization of cassava starch and the development of 4D-printed starch-based food. |
