Study On The Effect Mechanism Of Extrusion On The Quality Of Wheat Gluten-Peanut Oil Extrudates

The extrusion of wheat gluten produces a highly concentrated protein product with a taste and texture similar to that of animal muscle,and has great potential to improve the diet of the population as a substitute for animal protein as"meat analog".However,there are still problems with wheat gluten extrusion,of which the poor texture of the extrudate resulting the inferior taste to animal muscle and other textured vegetable proteins protein is one of the main constraints to its promotion and industrial production.The addition of lipid to protein raw materials reduces the thermo-mechanical effects of extrusion processing,and the interaction between protein and lipid components,which leads to changes in protein structure and affects the texture of the extrudate.The effects of extrusion parameters on the physicochemical properties of wheat gluten extrudate（WGE）and wheat gluten-peanut oil extrudate（WPE）were investigated;The influence of extrusion on the gluten structure and its components were investigated to reveal the molecular mechanisms of gluten aggregation and the intrinsic relationship between gluten aggregation and extrudate quality were investigated.The interactions between wheat gluten and peanut oil components in WPE during extrusion were clarified and the relationship between the interactions and the quality of WPE was explored.（1）The effect of extrusion on the physicochemical properties of WGE and WPE was investigated in comparison,combining the functional,physical,and textural properties of the extrudates with different oil contents to analyse the quality changes.Under the same extrusion conditions,WPE showed reduced water holding capacity（1.23±0.03～1.53±0.02g/g）,raised oil holding capacity（0.47±0.01～0.82±0.01 g/g）and rehydration（90.41±11.50～154.61±11.50）compared to WGE（1.56±0.02 g/g,0.61±0.01 g/g,100.72±9.10%）;the colour of WPE was darker than WGE,and from yellowish brown to dark brown with the amount of peanut oil,the bulk density of WPE was slightly higher（0.99±0.01～1.22±0.06g/cm³）compared to WGE（0.99±0.03 g/cm³）and the Archimedes density was less than（0.99±0.01～1.22±0.06 g/cm³）WGE（1.40±0.07 g/cm³）;The hardness of WPE（2471.51±123.06～10917.52±576.85 g）and chewiness（1029.50±59.62～5657.25±112.43 g）decreased,and elasticity increased（0.77±0.01～0.97±0.01）comparing WGE.The eating quality of WPE was improved compared to WGE.When peanut oil was added to the raw material at 2%（w/w）,the extrudate had the best edible quality with the highest sensory evaluation score（7.57）for rehydration（154.61±0.22%）,maximum elasticity（0.97±0.01）,moderate hardness（3600.45±948.88 g）and chewiness（2129.74±589.72 g）.（2）The effect of extrusion temperature on the rheological properties of the extrudate was investigated to explore the relationship between the the rheological properties such as viscoelasticity and creep properties and the quality of the extrudate.The results showed that wheat gluten and its components（gliadin and glutenin）had greater viscoelasticity and resistance to deformation than WGE,with glutenin being the main elastic component and gliadin the main viscous component in the extrudate.The dynamic modulus（G’,G’’）and creep strain of wheat gluten and their components in extrudates vary with extrusion temperature（100-180°C）in a composite power-law law model（G=K×f ⁿ）and a Burgers model（J（t）=J₁+J₂（1-exp（-t/τ_k））+t/η）.From 100°C to 140°C,the dynamic modulus of wheat gluten and glutenin increased and viscoelasticity increased,while the elasticity of the extrudate（WPE）increased（0.92±0.01～1.04±0.02）,further increasing the extrusion temperature led to a decrease in dynamic modulus,a decrease in viscoelasticity and a decrease in the elasticity of the extrudate;the creep strain of wheat gluten and glutenin decreased significantly and the resistance to deformation was reduced,while the hardness of the extrudate decreased significantly（7226.95±180.24 g to 1482.18±63.14 g）.（3）The effects of extrusion on wheat gluten and peanut oil were studied.The effects of extrusion temperature changes on gluten structure and oxidation characteristics of peanut oil were analysed,and the potential relationship between microscopic changes in components during extrusion and the extrudates quality was illustrated.The content of extractable gliadin decreased significantly（25.87%）when the extrusion temperature increased（100-180°C）;the content ofα-,β-andγ-gliadin decreased gradually;the relative content ofα-helices decreased（54.8%to 38.8%）,whileβ-sheets,β-turns and random coils increased.At 140°C,the molecular weight of glutenin increased significantly,and the resistance to deformation decreased.When reached 180°C,theα-helices structure was disrupted（35.2%）and moreβ-sheets,β-turns and random coils were formed.A gradual increase in the ratio ofβ-turns/β-sheets（0.50-1.08）in gluten decreased in resistance to deformation.An increase in extrusion temperature promotes an increase in the mean particle size of the wheat gluten and gluten aggregated through the formation of intra/inter disulphide bonds between gliadin and glutenin,and the aggregation behaviour is consistent with the first order exponential regression(Y=499.04+17866.47e^-x/30.51,WPE).From 100 to 160°C,the dynamic modulus of wheat gluten increased,and improved elasticity of the extrudate,suggesting that the aggregation of wheat gluten to some extent improved the extrudate elasticity,but that too much aggregation was detrimental to the improvement of the texture of the extrudate.The colour of peanut oil became darker,POV decreased,CV and p-AV increased and oxidation increased after extrusion processing.As the extrusion temperature increased（100-180°C）,the POV of peanut oil in WPE decreased by 0.36 mmol/kg,AV and CV increased by 1.32 mg/g and 3.19 mmol/kg,respectively,and p-AV increased by 5.69.The increase in extrusion temperature promoted the oxidation of peanut oil in WPE.Compared to the control group（PO）,the TOTOX of peanut oil in WPE was greater（100-140°C）and was influenced by the interaction between wheat gluten and peanut oil during extrusion,resulting in increased oxidation of peanut oil in WPE,and the colourful and flavourful oxidation products would contribute to the flavour and eating quality enhancement of WPE.（4）The investigation of the effect of interaction between wheat gluten and peanut oil during extrusion on the extrudate quality showed that covalent cross-linking of disulfide bonds in wheat gluten,oxidation-induced cross-linking and hydrophobic interactions between wheat gluten and peanut oil molecules affect the aggregation behaviour of wheat gluten in extrudates,and are intrinsic to the increased elasticity,reduced hardness and improved texture of extrudates.Extrusion temperature（100-180°C）would bring hydrophobic interaction in the extrudate strength decrease after rising first,carbonyl content and aggregation degree of wheat gluten increases,and larger particles between wheat gluten and peanut oil was formed,but too much wheat gluten aggregation would lead to extrudate stiff and loss of elasticity,which is not conducive to taste.The effect of peanut oil oxidation on the oxidation of wheat gluten mainly occurred when the extrusion temperature was100-140°C,and the carbonyl content of wheat gluten increased significantly（6.56nmol/mg）,and the oxidation rate of peanut oil increased faster（TOTOX increased 4.11）.Peanut oil molecules embedded in wheat gluten,the contact surface increased,and the grain size of wheat gluten cluster increased rapidly.When the extrusion temperature increased further,the gluten protein would still be further oxidized,but the rate slowed down.The oxidation of peanut oil could accelerate wheat gluten oxidation.In addition to the wheat gluten aggregation induced by extrusion temperature,the molecular interaction of WPE components based on co-oxidation is one of the important reasons for the increase of elasticity and the improvement of taste of WPE.