The Characteristics Of Wheat Starch Gels Molded By 3D Printing

3D printing technology has great potential in the field of food design and production.However,most of the printing materials studies at present focus on chocolate,dough,ice cream and hard candy and other materials,while there are few reports on starch as 3D printing materials.Starch exists in most green plants and is the most abundant carbohydrate source in human diet.It is composed of a large number of glucose units connected by glycosidic bonds and has the characteristics of high energy,low price and easy access.Starch after gelatinization as a 3D food printing material,has good mechanical and low-cost properties.Starch can be gelatinized under heating conditions to obtain the viscoelasticity and plasticity required as a suitable raw material for 3D printing.In this paper,the 3D printing characteristics of different starches were studied,and the effects of NaCl solution concentration,annealing treatment(ANN)and heat-moisture treatment(HMT)on the physicochemical and structural properties for wheat starch 3D printed samples were also explained.The main results are as follows:(1)The 3D printing properties of potato,wheat and corn starch were studied in the experiment.Potato,wheat and corn starch as 3D printing materials have good accuracy and reproducibility.The results showed that the samples printed from potato and corn starch had significant size shrinkage,while the size of the target model was precisely reduced by the printed sample by wheat starch.Starch color changed during gelatinization and printing.Wheat starch gel has the lowest viscosity,good extrusion capacity and nice storage performance,which makes the gel based on wheat starch less sticky wall and blocked nozzle in the process of 3D printing.Fourier transform infrared spectroscopy(FT-IR)showed that the gelatinized starch gels and the printed samples had no obvious structural changes.The change of texture was closely related to starch dehydration and regeneration during storage.In addition,the microstructures of the 3D-printed samples from wheat starch were more tightly ordered than those from potato and corn starch.In conclusion,it is preliminarily determined that wheat starch is more suitable for the development and utilization of 3D food printing materials.(2)The effects of NaCl concentration on the quality of 3D-printed wheat starch gel were explored in the experiment.Appropriate NaCl addition can help to change the gel characteristics,thus improving the gel extrusion and maintaining sufficient post-deposition viscosity to keep the shape of the product and extend the shelf life of the product.The results showed that when wheat starch contained 150 mM(mmol/L)NaCl,the support stability,line uniformity and height retention were relatively optimized.Low concentrations of NaCl solution(50 and 100 mM)enhanced the hydrogen chain polymerization of amylose and increased gel strength significantly.At higher concentrations of NaCl solution(150 and 200 mM),the Na⁺interacted with the hydroxyl groups in the starch molecules,which hindered the polymerization of the starch molecules and improved extrusion.The starch gel containing 150 mM NaCl showed moderate gel viscosity and strength,allowing for easy construction of the printed product.The new C-H bending vibrations that appeared in the gelatinized starch formed the tertiary complex of starch,water and salt,which determined structural functionality but did not result in new functional groups appearing in the gelatinized starch.Meanwhile,printed samples with gel containing 150 mM NaCl had a softer and more elastic texture after long-time storage because NaCl inhibited the retrogradation of starch gels.In conclusion,it can be preliminarily determined that adding 150 mM NaCl in wheat starch material can improve printing accuracy and stacking height.(3)The effects of HMT and ANN treatment on the physicochemical and structural properties on 3D printing of wheat starch were studied in the experiment.HMT can improve the 3D printing effect of wheat starch,significantly improving the accuracy and stacking height of 3D printed samples,and prolonging the storage time of 3D printed samples.The quality of 3D printing product by ANN wheat starch decreased,that the sample edge was rough,the stacked height of sample was reduced,and the sample hardness increased significantly after a long-time storage.The properties of the printed samples of native wheat starch were moderate,but better than that of ANN wheat starch.These results were related to the distribution of chain length and the molecular weight(Mw)and degree of polymerization(DP)of starch.The chain length of starch moved to the direction of short chain after HMT,resulting in a decrease in viscosity,easier extrusion,and smoother printing lines.The ANN effect is just the opposite,leading to poor printing effect.In conclusion,it can be preliminarily confirmed that the HMT can improve printing height and accuracy of wheat starch.