Protein Extraction Process Of Walnut Oil Cake And Its Antioxidant Activity

Faced with the dual pressures of shortage of edible protein and environmental protection,the utilization of forestry protein resources and product development have attracted worldwide attention.In recent years,the development and utilization of edible oil has been the focus of woody oil crops research,however,in this process,the reuse of cakes and the research and development of related products especially the utilization value of protein resources,were neglected.Walnut kernel contains 18%-24%protein,its protein content is as high as 40-50%after oil extraction,but it is usually used as animal feed,so that the walnut protein resources can not be fully utilized.Therefore,the development and utilization of walnut cakes will help improve the overall value of the walnut industry chain.This study aims at the comprehensive utilization of walnut cakes,and designs the extraction technology and antioxidant activity of walnut cake protein.Further more also aims to explore the utilization methods and approaches of walnut cakes and improve the application and range of walnuts in food,cosmetics,medicine and other fields.In this study,cold-pressed walnut cake was used as raw material to extract protein from walnut cake using sodium hydroxide,buffer and enzyme assisted method.With walnut butter cake protein yield as target,different extraction parameters were designed to obtain the best protein extraction conditions and the maximum protein yield.The effects of different experimental parameters on the yield of walnut cake protein were studied in depth.The results show that,the optimal extraction conditions for single factor extraction of walnut cake protein using alkaline extraction method are:When the concentration of Na OH solution was 90 m M,extraction time was 2 h,the particle size of walnut cake was 100mesh,and the ratio of solid to liquid was 1:40.The optimal extraction conditions for single factor extraction of walnut cake protein by buffer were:The p H of the buffer solution was9.0,the extraction time was 1 h,the particle size was 80 mesh,and the solid-liquid ratio was 1:50.The optimum extraction conditions for enzyme-assisted extraction of walnut cake protein were as follows:the addition amount was 3%,the particle size was 80 mesh,and the ratio of solid to liquid was 1:50.According to the results of single factor experiments,the appropriate extraction conditions were preliminarily screened.The optimum extraction conditions of protein in walnut cake were optimized by using response surface methodology(RSM).The protein yield of the walnut cake was used as the response value.Design The Box-Behnken the 4 factors and 3 levels experiment by using the center combination design.The alkaline extraction sodium hydroxide,buffer,enzyme-assisted and ultrafiltration were used as the extraction conditions for the walnut cake protein.The effect of the yield,and by comparison,the method parameters and processes for optimal extraction of walnut cake protein.The results show that(1)The order of factors affecting the extraction process of walnut cake protein by alkali extraction method is:particle size(X₄)>Na OH solution concentration(X₁)>solid-liquid ratio(X₃)>extraction time(X₂),and the optimum extraction process parameter is:Na OH solution concentration 90.85 m M,extraction time 1.576h,solid-liquid ratio 1:39.97(g/ml),particle size 85.51 mesh.The extraction yield of walnut cake protein reached 51.505%,and the protein yield model was highly significant(R²=0.96).(2)The buffer extraction method influences the sequence of the walnut cake protein extraction process factors as follows:buffer p H(X₁)>particle size(X₄)>buffer ratio(X₃)>extraction time(X₂),optimal extraction process The parameters are:buffer p H 8.912,extraction time 1.44h,solid-liquid ratio 1:48.33,particle size 60.300mesh.The yield of walnut cake protein reached 17.610%,and the protein yield extraction model was highly significant(R²=0.96).(3)Enzyme-assisted method The order of factors affecting the extraction process of walnut cake protein is:particle size(X₃)>extraction time(X₄)>?-enzyme addition volume(X₁)>solid-liquid ratio(X₂).The optimum extraction parameters were as follows:2.22%enzyme addition,1:30.27 ratio of solid to liquid,particle size 89.22 mesh and extraction time 0.98 h.The three methods for extracting walnut cake protein were all based on the best extraction parameters.The experimental results were all consistent with the yield of walnut cake protein obtained by response surface analysis,the error is less than 5%.Using the above experimental parameters and results,the antioxidant activity of walnut cake protein was measured and the effect of cellulose acetate membrane filtration on the antioxidant activity was examined.The results are as follows:The DPPH free radical scavenging rate of the alkali-extracted walnut cake protein ranged from 15.96-50.05%,the DPPH free radical scavenging range of the extracted walnut protein from the buffer solution ranged from 26.26-65.67%,and the DPPH free radical scavenging rate of the enzyme-assisted extraction walnut cake protein ranged from 46.49-60.94%.In the reducing power experiment,the absorbance value of the buffer extracted walnut protein is generally significantly higher than that obtained by the alkali extracted walnut protein.The DPPH radical scavenging rates of the alkaline extracted walnut cake proteins were 32.36%and 36.48%,the absorbance values in the reducing power experiment were 0.691 and 0.267 respectively,and the DPPH radical scavenging rates of the buffer extracted walnut cake proteins were 77.89%and 68.42%,Absorbance values in the reducing power experiment were 1.082 and 1.206,respectively,after filtration at 3k Da and 30k Da membranes.