Preparation And Process Optimization Of Textured Walnut Protein

In recent years,the walnut industry of our country develops rapidly,the walnut output increases rapidly.The high-value utilization of walnut by-products in deep processing and oil production is of great significance to the sustainable development of walnut industry.Walnut protein is a kind of high-quality plant protein,accounting for 15-20%of the walnut kernel.In this thesis,the main raw material is walnut protein extracted from walnut dregs after oil extraction,the effects of extrusion process parameters on the color,texture and texturization degree of textured walnut protein were studied,and the superfine grinding and ultrasonic treatment of walnut protein were carried out,the effects of modification on the color,texture and texturization degree of textured walnut protein and the addition of different proportions of soy protein isolate on texturized protein were studied.The purpose of this study is to make high-value use of walnut oil by-products and to provide theoretical support for using walnut protein as raw material of plant protein meat.The main findings are as follows:(1)Using single factor method,the effects of extrusion temperature(130℃～150℃),moisture content(45%～55%),screw speed(160 r/min～240 r/min),feeding speed(20 g/min～30 g/min)and cooling temperature(50℃～70℃)on textured walnut protein were studied.As the moisture content,feeding speed and cooling temperature increased,the color of textured walnut protein became lighter.With the increase of extrusion temperature and screw speed,the hardness and chewiness of textured walnut protein increased.With the increase of extrusion temperature and screw speed,the texturization degree of textured walnut protein decreased.The degree of organization increases with the increase of water content and cooling temperature.When the extrusion temperature was 135℃,the maximum texturization degree was 1.076.When the screw speed was 160 r/min,the maximum texturization degree was 1.094.When the moisture content was 52.5%,the maximum texturization degree was 1.142.When the cooling temperature was 65℃,the maximum texturization degree was 1.140.When the feeding speed was22.5 g/min,the maximum texturization degree was 1.15.There is no significant effect of extrusion temperature and cooling temperature on water holding capacity,screw speed and cooling temperature have no significant effect on oil holding capacity.According to the results of single factor experiment,three parameters of extrusion temperature,moisture content and feeding speed were selected as the response surface experiment factors,and the degree of texturization was taken as the response value,response surface analysis method was used to optimize the extrusion process parameters,and the results showed that the optimum extrusion process parameters were obtained as follows:extrusion temperature 141℃,moisture content 52.7%,screw rotation speed 160 r/min,feeding speed 26 g/min and cooling temperature 65℃,the degree of organization is 1.209.(2)The effects of superfine grinding and ultrasonic treatment on the structure and functional properties of walnut protein were studied,and the effects of modified walnut protein on the texturization were also studied.The results showed that the particle size of walnut protein decreased after superfine grinding and ultrasonic treatment.The minimum particle size of walnut protein after superfine grinding was 10.65 μm,and the minimum particle size of walnut protein after ultrasonic treatment was 39.15 μm.Scanning electron microscope(SEM)showed that the protein particles after ultra-fine grinding were smaller and more dispersed.After ultrasonic treatment,the particle size first decreased,then the aggregation increased.The results of Fourier transform infrared spectra(FTIR)showed that the content of β-sheet decreased and the content of β-turn increased significantly after superfine grinding,while the content of β-turn and irregular crimp structure increased after ultrasonic treatment.The highest content of sulfhydryl group was 30.01 μmol/g after superfine grinding at 35 Hz.The highest content of free sulfhydryl group was 25.49μmol/g after ultrasonic treatment for 8 min.After superfine grinding,the solubility and emulsifying activity of walnut protein increased at first and then decreased,and the maximum solubility of walnut protein was 28.10%after superfine grinding at 25 Hz,the maximum emulsifying activity was 49.31 m2/g,the water and oil holding capacity decreased significantly,the foaming and emulsifying stability increased significantly,the foaming property and emulsifying stability of the protein were 1.92 and 1.4 times as high as those of the raw material respectively.After ultrasonic treatment,the water-holding capacity,oil-holding capacity,solubility,foaming capacity,emulsifying activity and sulfhydryl group content of walnut protein decreased,and the foam stability and emulsifying stability decreased first and then increased.The oil-holding capacity reached the maximum value of 3.66 g/g after ultrasonic treatment for 6 min,which was 1.45 times higher than raw material.The foaming property reached the maximum value of 62.22%after ultrasonic treatment for 8 min.The solubility reached the maximum of 42.35%after ultrasonic treatment for 8 min.The maximum emulsifying activity was 47.19 m2/g after ultrasonic treatment for 10 min.The results of extrusion texturization of walnut protein obtained by superfine grinding at 25 Hz,35 Hz and ultrasonic treatment for 6 min,8 min showed that:The effects of different modification conditions on the color,hardness,elasticity,chewiness,texturization degree,water-holding capacity and oil-holding capacity of the textured walnut protein were observed.After superfine grinding and ultrasonic modification,the textured walnut protein became darker,hardness and the chewiness increased.The minimum L*value of superfine grinding was 29.63 after superfine grinding at 25 Hz,and the chewiness was the highest after superfine grinding at 35 Hz,the results showed that the degree of organization was worse,and the lowest degree of organization was 1.06 after superfine grinding at 25 Hz,which was 13.8%lower than that before modification,and the water-holding capacity was increased,but the oil-holding capacity was decreased,the water-holding capacity and oil-holding capacity were 0.42 g/g and 0.59 g/g respectively after ultrasonic treatment for 8 min.(3)The effect of soybean protein isolate(SPI)content on textured walnut protein was studied by adding 0%-20%SPI to walnut protein.The results showed that after adding soy protein isolate,the color of textured walnut protein became darker.With the addition of 15%soy protein isolate,the minimum L*value was 29.19,the color was the darkest.The hardness,elasticity and chewiness increased.The water-holding capacity increased,and the oil-holding capacity decreased.When the content of soybean protein isolate was 20%,the highest waterholding capacity of textured walnut protein was 0.48 g/g.The degree of texturization first decreased and then increased,when the content of soybean protein isolate was 5%,the minimum texturization degree of textured walnut protein was 1.13.When the content of soybean protein isolate was 20%,the maximum texturization degree was 1.305.The best textured protein was obtained by adding 20%soy protein isolate.