Extraction And Physicochemical Properties Of Protein From Flaxseed Cake

The average content of protein in flaxseed is 21% and that can be as high as 40% in the cake after removing the oil.Its amino acid profile is balanced,and the nutritional value is comparable to that of soybean protein.It is a high-quality protein resource.This paper will provide data and theoretical support for the further development and utilization of proteins from flaxseed cold-pressed cake.The research concentrates on the extraction technology and physicochemical properties of the proteins obtained.The alkaline-extraction and acid-precipitation method was used to separate the flaxseed protein from the cold-pressed flaxseed cake.The effects of extraction pH,temperature,time,and extraction solid-liquid ratio on protein recovery rate were investigated.On the basis of single factors experiment,the extraction technology of flaxseed protein isolate(FPI)was optimized using orthogonal design.The results showed that the optimal extraction conditions for the test were as follows: extract ion pH 9.5,extraction temperature 35 °C,extraction time 90 min and extraction solid-liquid ratio 1:30;The recovery rate of protein was 58.13%,and the protein content(dry basis)of the FPI was 84.32% after thrice verification experiments under the optimal conditions.The FPI was dried by vacuum freeze-drying and spray-drying.Its structural properties and functional properties were studied.The results showed that the drying method significantly affects the structural properties of the protein.The sulfhydryl groups of the two dried FPI products are exposed,and form disulfide bonds through oxidative cross-linking.The hydrophobic groups of both proteins increased,and apart from the increase in the content of ?-turns in the secondary structure,the contents of the other three structures reduced to varying degrees.The degree of protein structure change caused by spray drying was greater than that of vacuum freeze-drying,but the drying method did not affect the subunit structure of protein;The microstructures of the proteins by two drying methods are quite different.The former shows a ellipsoidal structure with wrinkles and the latter has a lamellar structure with loose pores.The bulk density of the former is higher than that of the latter.Structural properties affect the functional properties of proteins.The solubility,water holding capacity,oil absorption,emulsifying capacity and foaming stability of the freeze dried protein were higher than those of the spray dried protein,while the latter had higher foaming capacity than the former.Flaxseed protein concentrate(FPC)is prepared by alcohol leaching method.Ethanol concentration,extraction time,extraction solid-liquid ratio,extraction temperature,and time of alcohol wash were used as single factors,with the protein content of FPC recovered as the target.The orthogonal design experiment was used to optimize the extraction technology of FPC.The results were as follows: ethanol concentration 70%,solid-liquid ratio 1:16,extraction temperature 50 °C,extraction 40 min and alcohol wash 2 times;the recovery of protein was 75.82% and the protein content was 56.19% under this condition.Ultrafiltered flaxseed protein concentrate(UFPC)and ultrasound-assisted flaxseed protein isolate(USPI)were also prepared,and the functional properties of FPI,FPC,UFPC,USPC and commercially available soybean protein isolate(SPI)were compared.The content of major anti-nutritional factors of four self-made protein products as above were tested.The results showed that water holding c apacity and oil absorption of the four protein products were better than that of the SPI,especially the water holding capacity of FPC,which was 11.52 g/g under neutral conditions,but the solubility and interface properties were poor;Foaming properties,water holding capacity and oil absorption of FPI were superior to those of SPI,but its solubility and emulsifying properties were poor.The protein content of USPI after ultrasonic-assisted extraction was higher than that of FPI protein,with the content of soluble sugar reduced.The solubility,water holding capacity,oil absorption,emulsifying property and foaming stability all had great improvement.Except for its solubility was slightly lower than SPI,other functional properties were better than those of SPI.The content of cyanogenic glycosides in the four proteins was lower than that in the raw materials(RM),especially in UFPC prepared by ultrafiltration,was not detected in the product;The extraction methods also greatly reduced the content of phytic acid in the protein products,which had a certain improvement on their nutritional value.Alcohol washing and ultrafiltration have a good removal result on tannic acid in flaxseed protein.Ultrasonic wave treatment increases the dissolution of the three anti-nutritional factors due to its cavitation,so that the contents of all anti-nutritional factors in USPI were higher than those of FPI.