Study On Extrusion 3D Printing And Post-processing Adaptability Of Mashed Potato And Its Starch Mixed Gel System

3D food printing,as a new food manufacturing technology,has attracted considerable attention in recent years.In consideration of the complexity and diversity of food materials,it is highly required to clarify the relationship between material properties and 3D printing behavior.However,currently,it is still not clear.In addition,the researches on 3D food printing are mainly focused on the material properties affecting the 3D printing behavior,while its specific advantages have not been involved enough.Apart from ready-to-eat 3D printed foods,many foods require further post-processing after printing.However,the information about the structural stability,color and shape changes of 3D printed foods during post-processing is still very lacking.This greatly limits the popularization and application of3D printing.In consideration of these problems faced by 3D food printing,this project firstly studied and clarified the relationship between material properties and 3D printing behavior,and the corresponding mechanism.Afterwards,the possibility of regulating texture characteristics and product quality of 3D printed ready-to-eat mashed potato?MP?was investigated by customized designing internal structure.Finally,the structural stability,color and morphology changes during different post-processing methods were studied.Specific work was as follows:1)Based on the extrusion-based 3D printing,potato starch,k-carrageenan?KG?,and xanthan gum?XG?were selected to form a gel system to establish the relationship between material properties and 3D printing behavior.Firstly,the specific material characteristics that affect different stage performance during printing process were correlated.The 3D printing performance of the gel system was then discussed.Results indicated that thermodynamic properties of the gel system significantly affected the selection of suitable 3D printing temperature;in the extrusion stage,the flow stress??_f?,apparent viscosity???,consistency coefficient?K?and shear-thinning property significantly affected the extrusion performance;in the recovery stage,a short gelation time?temperature recovery behavior?and a fast recovery of mechanical strength?shear recoverability?were beneficial to improve the 3D printing accuracy;in the self-supporting stage,the material's?_f,elastic modulus?G??and complex modulus?G*?determined the stability of 3D printed structures.Lastly,the flow chart of the relationship between material properties and 3D printing characteristics was raised,which provided some useful information for the 3D printing of other food materials.2)The actual food system-MP was furtherly used to verify the relevant conclusions established in the previous chapter based on the gel system.After determining MP's optimal ratio of potato flakes to boiling water,different gums?KG,XG,guar gum?GG??were then added to furtherly improve MP's 3D printing performance.Results furtherly indicated that the?_f,?and shear-thinning characteristics significantly affected MP's extrusion performance in the extrusion stage.The shear recoverability in the recovery stage and the G?,G*and?_f in the self-supporting stage considerably affected MP's 3D printing accuracy and 3D printed structure's stability.KG-MP,with the highest?and?_f,illustrating a brittle and hard texture,was easy to break during the extrusion stage and the 3D printing accuracy was poor.XG-MP was easily to be smoothly extruded due to the low?and?_f,but the stability of 3D printed structure was poor during self-supporting stage due to poor mechanical strength??_f,G?and G*?.KG-XG-MP showed both good extrusion performance and self-supporting capability,illustrating the best printing quality.3)Using KG-XG-MP as material,printing parameters were firstly optimized to create a fine internal structure of 3D printed MP.Results indicated that the nozzle diameter,printing height,and printing speed significantly affected the printing accuracy or printing efficiency.3D printing could realize the accurate creation of designed internal structure of MP.The hardness,adhesiveness,and other texture properties of 3D printed MP were significantly affected by the internal structure.For example,for the samples with a perimeter of 3 and honeycomb infill,the hardness increased from 101.21 g to 432.21 g when the infill level increased from 10%to 70%.Compared with mold-made samples,the 3D printed MP illustrated a softer texture.This research provides a new perspective for the future production of 3D printed food with adjustable texture.4)Combined with designing internal structure,air frying was used as post-processing method to study the structural stability,texture regulation,and oil reduction possibility of 3D printed potato-based snack.Results indicated that air frying could well maintain the 3D printed structural information.The infill level and infill pattern significantly affected textural properties of 3D printed air-fried products.Mold-made samples were not suitable for air frying post-processing.Compared with traditional frying,air-fried samples illustrated lower oil content?13.47%?.5)Using microwave as post-processing method,the p H-triggered 4D color change of printed foods,containing curcumin or anthocyanidin,was studied.Results indicated that,in the 3D printed stacked structure using MP?containing anthocyanin?and lemon juice-starch gel,microwave heating could accelerate the color change rate,and the color change rate was positively correlated with water mobility,but negatively correlated with the mechanical strength of gel system.In the 3D printed MP samples,during microwave heating,the curcumin emulsion structure was destroyed,and HCO₃^-was decomposed into CO₃^2-to enhance alkalinity.This resulted in a controllable color change of samples,and accordingly,hidden information in 3D printed nested structures was displayed by color change during microwave post-processing.6)Using dehydration technology as post-processing method,the automatic shape-change of 4D printed potato gel structure was investigated.Results suggested that,there was a critical value of adhesion property?adhesiveness?14.54 mm,work of adhesion?1331.95 g.mm?for the materials to ensure the smart shape evolution of 3D printed samples during dehydration process.The bending degree of microwave dehydration?MD?sample was positively correlated with the shrinkage ratio,but negatively correlated with the???of material.The internal heating mechanism in MD was not conducive to the shape-change.The surface heating mechanism of AD and the“stack bending effect”contributed to the bending evolution of samples.The bending degree of hot air dehydration?AD?samples was higher than that of MD samples and infrared dehydration?ID?samples.The bending direction of samples was perpendicular to the printing path,and the bending degree was affected by the aspect ratio,infill level,and height.