| 3D printing,commonly referred to as additive manufacturing(AM),has received a great attention from industry,academic and the public due to its numerous advantages.It offers shorter production runs compared with traditional manufacturing methods.In addition,it can generate various complex shapes by using limited mass of materials with an enhancement of mechanical properties.For food sector,3D printing provides a new frontier in food processing.It helps us to realize and produce new foods with complicated shapes using particular material formulation mixtures.The purpose of applying AM technology to printing food materials is to simplify the production process and combine the design of a food with new textures and potentially enhance its nutritional value.A wide range of foods can be used as raw material for 3D printing,basically any food type that can be extruded and that will hold its shape afterwards,with or without glue-like components.Surimi,a typical intermediate fish product,is a viscous food gel system and that can be a promising food material for developing various 3D constructs.In this paper,the surimi gel system formed by gluconate lactone(GDL)was used as 3D printing food material,and the mechanical properties of the gel system were improved by adding the auxiliary materials to the 3D printing technology.Based on the suitability of 3D printing of surimi gel,the effect of 3D printing process parameters on the print quality and precision of surimi gel system were studied.The mechanism of lipid peroxidation in the process of storage of fibrin was established.With a view to further clarify the relationships between food material structure,printing characteristics and printing process during the processing and storage process.This study has laid a theoretical basis and practical application for understanding the application of meat gel system in 3D printing technology.First,the formation process of GDL-induced silver carp(Hypophthalmichthys molitrix)surimi gel system was studied.Results showed that the optimum concentration of GDL was 1.0%.Under this condition,the pH of surimi gel dropped to about 4.5 quickly during the gelatinization time of 4h.Moderate GDL addition could enhance the gel strength of surimi and form a dense-uniform gel network structure,which might be attributed to the secondary structure changes of myofibrillar induced by GDL.In addition,the main forces to maintain the GDL-MP structure are hydrophobic,disulfide and non-disulfide covalent bonds.However,the excess GDL addition could reduce the gel properties of the surimi gel,leading to gel cracking.The relaxation stress,creep characteristics,apparent viscosity and dynamic rheology of the gel system were improved by adding NaCl and emulsified fat,and eventually,the obtained surimi gel system is more suitable for three-dimensional printing.The results show that NaCl addition could significantly improve the relaxation stress,creep characteristics and dynamic rheological properties of the surimi gel,which is helpful to improve the supporting force of the printing line,the moldability of the surimi gel,and the apparent viscosity which facilitates the smooth discharge of the 3D printing feed system.10% of the emulsified fat could significantly improve the relaxation stress,creep characteristics and dynamic rheological properties of the surimi gel,but the apparent viscosity tends to decrease gradually.However,the excess fat addition reduced the the viscosity of the surimi gel system,which was detrimental to the 3D printing system.Moreover,the structure of printed sample tends to be collapse and deform.The influence of the 3D printing parameters such as layer height,printing speed,nozzle diameter,extrusion amount and printing temperature on the extrusion quality of printed samples was studied.At the same time,the relationship between the key processing parameters was determined.The results showed that the optimal print parameters are as follows: layer height1.5 mm,printing height 5 mm,nozzle diameter 2.0 mm,printing speed 28 mm/s,printing temperature 45 °C and discharge rate 0.003 cm3/s.In addition,there is a certain relationship between the discharge rate Vd,print rate Vn and nozzle diameter Dn,so the print process should be integrated control of these three parameters to improve the printing accuracy.The relationship between the screw speed and the discharge rate during the extrusion of the 3D printing screw was modeled and analyzed numerically,and the results of the numerical analysis were verified by a simple printing model.The verification test showed that the stability of the extrusion process was significantly improved through this model,which could reduce the printing error and improve the printing accuracy of printed samples to a certain extent.The changes of fat oxidation,protein oxidation,fish water holding capacity,gel strength and 3D printing characteristics of the surimi at different storage temperatures were investigated.The results showed that with the prolongation of the storage time,the protein and the fat oxidation were accelerated,resulting in a decrease in overall freshness of the sample.At the same time,water retention,gel strength,gel elasticity,relaxation stress,creep characteristics and apparent viscosity were significantly reduced.The overall trend of each index is similar,and a relatively higher the storage temperature,the faster the oxidative deterioration occurs.In addition,a mathematical model was established to predict the degree of protein oxidation and the change of the printing characteristics of the surimi gel under different temperature storage based on the global stability index method(GSI).The numerical simulation was GSI=1-5.6161texp(-20.9159/RT).Oxidized linoleic acid(OLA)and malondialdehyde(MDA)lipid peroxidation system were used to study the effects of lipid peroxides on the structure of myofibrillar and the degree of myofibrillar protein.The mechanism of MP oxidation induced by fat oxidationand was described by measuring the protein gel strength,water holding capacity,water status and microstructure of oxidized surimi gel.Results showed that the apparent viscosity,yield stress and dynamic rheological properties could be improved induced by lipid peroxides(OLA and MDA).The extent of MDA induced protein oxidation was significantly higher than the OLA system.When the MDA concentration reached 0.03%,the surimi gel showed a solid-like state characteristic in short time,resulting in continuously feeding difficult to achieve.Effects of Malondialdehyde(MDA)-induced modification on water distribution in myofibrillar proteins gels were investigated using nuclear magnetic resonance(NMR)and magnetic resonance imaging(MRI).Results indicated that the water functionality was strongly affected by the modification level,which corresponded to the changes of water holding capacity of MP upon MDA modification.Besides,the P23(free water)of heated MP samples was elevated significantly compared with unheated MP samples. |
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