Study On The Kinetics Of Extrusion Quality Change Of Jerky And Its Orientation Mechanism

With the rapid development of our society,people start to pay more and more attention to the food quality.During the extrusion process of jerky,the raw materials are subjected to high temperature,high pressure,and high shear.Compound jerky with prickly pear added is rich in heat sensitive nutrient,which would definitely change during the extrusion process.However,the way it changes and the corresponding changing principle are not clear.The extruded jerky is popular among consumers,due to its unique texture and muscle fiber structure.The orientation degree is considered as an important index to measure the degree of muscle fiber structure,but the formation mechanism of the orientation degree of is not clear till now.Additionally,the influence mechanism on the orientation degree is not clear as well.In order to solve the above-mentioned problems,the vitamin C content and loss kinetics of the compound beef jerky with prickly pear added were studied in this thesis.By combining the characteristics of muscle fiber and polymer physical theory,the formation mechanism of extruded jerky orientation was studied.The specific research contents are as follows:(1)The content of vitamin C in the extruded beef jerky with prickly pear added was studied by changing barrel temperature,screw speed,and the amount of prickly pear addition.The results showed that the loss rate of vitamin C was about 28.53?57.28%during the extrusion process.The effect of the prickly pear amount and the screw speed on the loss rate of vitamin C was mainly induced by average residence time.And the effects of barrel temperature on the loss rate of vitamin C was induced by barrel temperature and average residence time.The average residence time was about 84.84 s and the loss rate of vitamin C was at 28.53%when the barrel temperature,screw speed,and the addition amount of prickly was at 140?,201.6r/min,and 20%,respectively.In addition,the results of loss kinetics showed that the reaction order of vitamin C loss was at one.Moreover,the iterative method was used to calculate the loss constant of vitamin C under different extrusion conditions between 0.00397 and 0.00772 s^-1.The Arrhenius equation was used to obtain the activation energy(18.06 k J/mol)and the factor k₀(1.0652 s^-1)of vitamin C.(2)Meat materials including pork,beef,chicken,and duck,were used to compare the application scope of commonly used characteristics of muscle fiber structure.The mechanism of muscle fiber characteristics on fresh meat and jerky was studied in this thesis.The results showed that the degree of muscle fiber structure of fresh meat was expressed by texture.While the degree of muscle fiber structure of the extruded jerky can be described by shear force,tenderness,and the degree of orientation.Additionally,scanning electron microscopy(SEM)and stereo microscope(SM)were used to verify the degree of muscle fiber structure.By comparing the muscle fiber diameter of pork,beef,chicken,and duck,and also the effect of meat materials on the degree of orientation,the degree of orientation was increased with the increasing muscle fiber diameter under the above-mentioned methods.(3)The polymer physics theory was used to analyze the rheological properties of raw material of extruded meat jerky.Rheological parameters of the extruded jerky were measured by the advanced rheological expansion system.With high muscle fiber contents,the storage modulus(G')and loss modulus(G")of the extruded jerky were independent from the phase difference(Tan?),showing the typical rubber characteristics.However,the dynamic viscosity(?')of three samples decreased with the increased shear frequency(?),indicating that the characteristics of shear thinning.In addition,the degree of orientation increased with muscle fiber content.The results showed that G',G",?and?'were positively correlated with the orientation degree of the extruded jerky,while?was negatively correlated with the orientation degree.With higher content of muscle fiber in the raw material system,the Wiesenberg effect was more significant during the extrusion process.Thus,the orientation degree of the extruded jerky was higher in the sample with better orientation effect.In summary,the kinetic parameters of the thermal sensitive material under high temperature,high pressure,and high shear were determined in this study.And the theory of polymer physics was used to analyze the formation mechanism of the orientation degree of muscle fiber.Besides,the formation mechanism of muscle fiber orientation was analyzed from the perspective of muscle fiber.Therefore,this study is useful while calculating the extrusion parameters of different kinds of extruded jerky,to save cost for developing new products,to provide theoretical basis for industrial products,and to accelerate the development of extrusion process changing from"black box"to"white box"operation.