Soybean Hydraulic Cold Pressing Process And The Aqueous Extraction Soybean Protein Isolate

In recent years,with the continuous improvement of people’s health awareness,the vegetable protein market has grown rapidly.In the vegetable protein market,soybean protein is the most widely used due to its high nutritional value and excellent functional properties.However,the problem of organic solvent residues in industrial production limits the application of soybean protein in green food,organic food and other fields.On the basis of studying the theory of soybean hydraulic pressing,this study uses hydraulic cold-pressed soybean cake as raw material to extract soybean protein.Through this study,we develop a green processing route of soybean protein isolate by combining pressing and aqueous extraction.This route guarantees the protein content of the product is 90%,while there is no organic solvent and enzyme are introduced.The main findings are as follows:Firstly,the effects of different pressing methods on soybean protein extraction were studied.The results showed that the protein denaturation level of the cake by the screw pressing method was high,and the lipid and protein were closely combined by shearing,while the cake by the hydraulic pressing method had a low level of protein denaturation and binding of lipid to proteins.The protein yields of the soybean meal from the screw pressing method and the hydraulic pressing method were 63.08% and 79.60%,respectively,and the protein contents were 79.58% and 83.66%,respectively.Therefore,the hydraulic pressing method was determined to prepare the defatted soybean cake.Secondly,the changes of the pressing characteristics during the hydraulic pressing of soybean were investigated,and peanuts and peas were used as controls.The results showed that the basic components had a great impact on the pressing characteristics of soybean.Peanut and pea as the control,peanut had the softest texture,the highest compression ratio and cell breakage rate,and the smallest porosity;pea had the hardest texture and compressed,the compression ratio and cell breakage rate were the smallest,and the porosity was the largest;while the texture of soybean was between the two sample,and the indicators of the pressing characteristics were also between the two sample.The content of different basic components had a great influence on the soybean pressing characteristics.During the pressing process,soybean fiber played an important role in maintaining the cake structure and retaining lipid.Then,the changes of soybean hydraulic cold pressing process and pressing characteristics were explored.The results showed that the residual oil rate of the cake was less than 5% when the water content was 8%,the pressing pressure was 80 MPa,the pressing temperature was80℃,the pressing time was 30 min,and the cake was pressed twice.With the increase of the layer height,the residual oil rate of the cake increased,the compression ratio decreased,the porosity increased,the permeability increased,the cell breakage rate decreased,and more lipid remained within the cellular structure.In order to improve the pressing efficiency,the residual oil rate of the first pressing can be reduced to 6% after the soybean was rolled.When the particle size of the material was 30 meshes,the residual oil rate of the cake meal was only 5%.Next,the process of preparing soybean protein isolate by extraction and separation and precipitation of cold-pressed cake was studied.The results showed that when the fractionation centrifugation was p H 6.8,the aqueous temperature was 4℃,and centrifugation at 12,000 × g for 20 min,the effective separation of protein and lipid could be achieved;adjusted the supernatant p H 4.5 could obtained the soy protein isolate(CSPI),its protein contents was90.85%,the protein yield was 61.21%;at the same time,the precipitated part could be used as soybean protein concentrate(CSPI),its protein content was 76.77%,and the protein yield was20.85%.Through the analysis of functional properties,it was found that the solubility of CSPI was comparable to that of solvent-extraction soybean protein isolate(SSPI),and the emulsifying properties,emulsifying stability,water holding capacity and oil holding capacity were all higher than those of SSPI.Finally,on the basis of this experimental study,the calculation and selection of equipment for the aqueous extraction soybean protein production line with an annual output of 300 tons has been completed,which has good economic benefits and social value.