Study On Protein Extraction Technology And Functional Characteristics Of Hempseed Protein Isolated

Hempseed is a new protein resource with rich of fat and protein which has attracted the attention of scientific researchers and consumers.The hempseed protein isolates(HPI)extraction technology,physical and chemical properties,effect of heat treatment on HPI functional characteristics and the structure,and application of HPI for Pickering emulsion were studied in this paper to improve the HPI extraction rate,reveal the mechanism of effect of heat treatment on HPI functional properties and structure and expand of HPI product application.It provides a theoretical basis and guidance for improving the utilization rate of hemp resources,broadening the development direction of the hemp industry,as well as industrial production and practical application of HPI.The main contents and results of the study are as following:First,the optimal extraction process of HPI was obtained by the response surface method.On this basis,the composition and emulsifying properties of the HPI were studied.The results showed that the optimum extraction parameters of HPI was as following:ratio of solid to liquid was 1:20,duration time was 70 min,temperature was 44℃,pH was 8.3 and the protein extraction rate was(39.15±0.28)%,with a protein content of 93.54%.Hempseed protein consists mainly of globulin(edestin)and albumin.By SDS-PAGE,The protein subunits of HPI were distributed in the range of 20-50 kDa.The globulin and albumin account for 76.41%and 23.59%of HPI.Hempseed globulin was composed of acidic subunits and basic subunits with molecular weights of 37 kDa and 21 kDa,respectively.The isoelectric point of HPI was pH 4.7.With the increase of pH,HPI was highly soluble.Therefore,when the pH was greater than 12,the solubility was as high as 80%indicating that HPI was a typical alkali-soluble protein with the water holding capacity of 2.39±0.07g.Water/g protein and the oil holding capacity of 4.92±0.01mL oil/g protein.Emulsification and solubility were positively correlated,and the maximum value of emulsification stability was 78.3%at pH 7.Under different pH conditions,the droplet change trend of HPI emulsion was basically the same as that of emulsification.The foaming ability of HPI was significantly lower than that of SPI.The foam stability was significantly higher than that of SPI,which was related to the loose network structure of protein molecules.Secondly,the effects of heat treatment(25~95℃)on the structure and functional characteristics of the protein were studied by measuring the particle size distribution,solubility,emulsification and protein conformation changes under different temperature conditions.The results showed that the solubility and emulsification of HPI reached the maximum after treatment at 55℃,and the maximum was 265.88m~2/g.The results of FT-IR spectroscopy showed that the amide I band of protein isolated from HPI red shifted to the direction of low wave number with the increase of temperature,and the conformation of HPI was significantly changed by heat treatment.The content ofα-helix decreased significantly.in the process of heating,theβ-corner andβ-fold contents showed a tendency of increasing first and then decreasing indicating that the enhancement of heat treatment degree led to the transformation of part of the ordered structure to the irregular curly structure.The UV-absorption intensity increased and became stable,indicating that theα-helix of the secondary structure of HPI was destroyed to a greater extent,which was consistent with the conclusion of FT-IR spectrum.Protein aggregation was caused by thermal denaturation of proteins,and the microscopic morphology showed that the morphology of HPI at different heat treatment temperatures increased with the increase of temperature,and the protein molecule size increased,and the shape changed from gravel to large irregular aggregates.Again,a stable Pickering emulsion was prepared by the combination of encephalin and HPI.The effects of different amounts of encephalin on the size distribution,apparent viscosity,storage stability and micromorphology of the Pickering emulsion were studied.The results showed that the PDI index was the lowest,the dispersion was good,the system was homogeneous,the potential was-27.0mV.With the increase of the shear rate,the emulsion viscosity was the smallest when 10%of encephalin was added.The reason was that the oil droplets in the state of agglutination separated from each other during the shearing process.When 30%of encephalin was added,the PDI dispersion index was the lowest.When the amount of encephalin was 20%,the emulsion had the best storability.Optical microscope showed that the emulsion droplets without adding encephalin were large and unevenly distributed.With the increase of the amount of adding encephalin,the emulsion particle size was uniform and evenly distributed,without obvious droplet aggregation.