| Textured plant proteins,which were produced by extrusion,have become a research hotspot because of their meat-like fiber and taste.However,during the extrusion process,the state of the material cannot be monitored in real time which lead to the unknown about the mechanism of fibrous structure formation.Furthermore,the fiber structure cannot be regulated.As a result,the application and development of the textured protein are greatly restricted.Therefore,this study started from the research of extrusion process of textured wheat protein(TWG).Based on the optimal extrusion conditions,the different kinds of food additions were added during the extrusion process to change the crosslinking of wheat protein in the extrusion process.Thus,the influence mechanism of different protein modification methods on TWG qualities was revealed in multiple dimensions.In addition,food oral processing behavior method was used to explore the effects of different modification methods of wheat protein on the oral processing characteristics of TWG.Moreover,the difference between the TWG and real meat products was also investigated.The influence of starch ratio in raw materials and extrusion parameters on the qualities of TWG was studied and the optimal extrusion conditions for TWG were clarified.The results showed that the fluidity of the melt during the extrusion process was increased with the increase of starch content.Besides that,the bulk density of the TWG and the specific mechanical energy in the extrusion process was also decreased,which eventually lead to a significantly decrease in hardness of TWG to 2987.14 g.The screw speed and the amount of material added were closely related to the residence time of the material in the extrusion sleeve.Lower screw speed or the higher amount of material added lead to a significantly(p<0.05)increase in hardness of TWG.Higher water addition led to a significantly(p<0.05)increase in hardness and chewiness of TWG to 5251.45 g and 627.39 g·sec.The high extrusion temperature was conducive to the formation of internal fibrous structure in TWG.However,excessive high temperatures caused a significantly decrease degree of texturization of TWG.On the basis of suitable extrusion conditions,the influence of sodium chloride(0%-10%)on the qualities of TWG was studied.With the increase of sodium chloride content(0%-10%),the hardness,elasticity,and chewiness of TWG showed a significantly(p<0.05)increase to6758.23 g,0.93 and 1203.78 g·sec,respectively.The highest degree of texturization was 2.43 and obtained at 3% addition.The addition of sodium chloride reduced the expansion ratio and the whiteness of TWG.The microstructure results showed that the internal fibrous structure of TWG was gradually strengthened under the low concentration(0%-3%)addition.However,the internal fiber structure was collapsed and porous with the high concentration(5%-10%)addition.The analysis of protein polymerization behaviors concluded that wheat protein showed a polymerization tendency with the increase of sodium chloride addition(0%-3%)and the wheat protein was depolymerized with the addition of 5%-10%.The intermolecular forces and protein secondary structure results concluded that the molecular conformation changed under the addition of low concentrations.Specifically,the levels of β-sheet and disulfide bonds were increased with the addition of sodium chloride(0%-3%).However,the levels of α-helix and random coil were increased and the hydrophobic effect was also enhanced with the addition of high concentrations,which means a hindrance of cross-linking in protein and the decline qualities of TWG.The egg white protein(0%-2%)were added to the wheat protein and their influence on the qualities of TWG was studied.With the increase of egg white protein content,the quality of texture wheat protein was significantly(p<0.05)improved.However,there was no significant(p<0.05)difference between the addition of 1% and 2%.Both the visual and microscopic diagrams of the fibrous structure results showed that egg white protein promoted the formation of fibrous structure inside the TWG.The results of protein polymerization behavior showed that egg white protein reduced the content of sodium lauryl sulfonate(SDS)extractable protein,and formed a protein polymer with a higher molecular weight.The results of the intermolecular force showed that the addition of egg white protein reduced the hydrophobic interaction between protein molecules,and increased the disulfide bond content of wheat tissue protein significantly(p<0.05).At the same time,egg white protein increases the β-sheet content of the TWG and the elastic modulus(G′)and viscous modulus(G′′).The effect of sodium tripolyphosphate,sodium pyrophosphate and sodium hexametaphosphate(0%-2%)on the qualities of TWG were studied.The addition of sodium tripolyphosphate improved the hardness,elasticity,and chewiness of TWG.However,the addition of sodium pyrophosphate and sodium hexametaphosphate reduced the qualities of TWG.The microstructure results showed that sodium tripolyphosphate promoted the formation of fibrous structure in TWG,while sodium pyrophosphate and sodium hexametaphosphate addition showed the opposite results.The addition of sodium pyrophosphate and sodium hexametaphosphate showed more flake structures.The results of protein polymerization behavior showed that sodium tripolyphosphate reduced the proportion of protein SDS extractable proteins and free thiol groups,improved the levels of disulfide bonds and β-sheet in proteins and the thermal stability of proteins.The addition of sodium pyrophosphate and sodium hexametaphosphate reduced the degree of protein polymerization and the content of macromolecular proteins.At the same time,X-diffraction photoelectron spectroscopy(XPS)results showed that sodium tripolyphosphate was linked to proteins in the form of C-N-P,which increased the content of large molecular weight protein polymers and changed the surface charge of proteins.The dynamic rheological results showed that sodium tripolyphosphate addition reduced the elastic modulus(G′)and viscous modulus(G′′)of TWG.The influence of transglutaminase(TGase,0%-2%)on the qualities of TWG was studied.The hardness of TWG significantly(p<0.05)increased with the increase of TGase addition and highest value of elasticity and chewiness was obtained at 0.2% addition.The visual and microscopic result showed that the best internal fibrous structure of the TWG was obtained at0.2%.Further analysis results showed that TGase addition reduced the free lysine content in the TWG and promoted isopeptide bond crosslinking in protein.The content of SDS extractable protein showed a decreasing tendency first and then increasing and the protein polymerized first and then depolymerized,with the highest degree of polymerization at the addition of 0.2%TGase.The results of the protein intermolecular forces and protein conformation showed that under the addition of low concentration,TGase changed the protein conformation,promoted the crosslinking of disulfide bonds,increased the content of β-sheet The content of disulfide bonds under the addition of high concentrations(0.5%-2%)was reduced.The different TWG prepared based on different modification methods of proteins were compared with pork and chicken and the correlation between oral processing parameters and protein internal forces was established.The results showed that the value of saliva content,the number of chewing,chewing time and integral EMG were the highest in the sodium chloride group.The integrated value showed that there was a highly significant(p<0.01)difference between the sodium chloride,sodium pyrophosphate and sodium hexametaphosphate with pork and there was no significant(p>0.05)difference between sodium tripolyphosphate and egg white protein with chicken meat.The number of chews showed that there was a significant(p<0.05)difference TWG and pork and there was no significant(p>0.05)difference between egg white protein and sodium tripolyphosphate with chicken meat.The chewing time showed that there was a significant(p<0.05)between the sodium chloride and sodium hexametaphosphate with pork and there was no significant(p>0.05)difference between sodium tripolyphosphate,egg white protein and TGase with chicken meat.The content of saliva showed that there was no significant(p>0.05)difference between egg white protein,sodium pyrophosphate and TGase with pork and there was a significant(p<0.05)between the sodium chloride,sodium pyrophosphate and TGase with chicken meat.The correlation between the protein internal forces and the oral processing parameters showed that there was a significant correlation between the protein crosslinking and the oral processing parameters. |
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