| Soybean protein is rich in nutritional value,and soybean protein has some functional characteristics(such as emulsification,gelation,etc.)to make it widely used in the food industry.However,soybean protein is sensitive to processing conditions(temperature,pH,ionic strength,etc.),which limits the functional properties,so it is necessary to modify soybean protein.The glycosylation modification of protein can effectively improve its functional properties.On the basis of the original experiment,this experiment chose to modify soybean protein by papain restriction hydrolysis(DH≤2%)combined with transglutaminase(TGase)catalytic glucosamine glycosylation.The preparation of hydrolysis degree(DH%)for 0,0.5,1.0,1.5,2.0 soybean protease were modified by glycosylation,and samples M0,M0.5,M1.0,M1.5 and M2.0 were obtained.The amount of glucosamine in the samples were determined by high performance liquid chromatography(HPLC).The changes of molecular weight were determined by polyacrylamide electrophoresis(SDS-PAGE),the structural changes were determined by Fourier infrared spectroscopy(FT-IR),and the free amino acids,disulfide bonds and surface hydrophobicity of the products were characterized by structural characterization of the products.The effects of enzymatic hydrolysis and glucosamine glycosylation on the functional characteristics of soybean protein(solubility,emulsification,foaming,water retention,oil holding,gelation,in vitro digestion,etc.)were determined.And the high emulsifying soybean protein was prepared and the ability of stable emulsion system was studied.The results of the study were as follows:(1)HPLC analysis showed that the amount of glucosamine in M0 was 19.3 g/kg,soybean protease extracted more glucosamine,and the amount of glucosamine in M0.5,M1.0,M1.5 and M2.0 reached to 21.3,22.5,23.3,23.7g/kg,respectively.SDS-PAGE analysis showed that M0 had macromolecule polymers,M0.5,M1.0,M1.5 and M2.0 showed a decreasing trend with the increase of hydrolysis degree.The amount of free amino acids in Mo was lower than that of soybean protein.While the amount of free amino acids in M0.5,M1.0,M1.5 and M2.0 increased significantly,and were 0.92,1.37,1.72 and 2.21 mol/kg respectively.The amount of disulfide bonds in M0,M0.5,M1.0,M1.5 and M2.0 decreased significantly(Reduced from 0.62 to 0.49,0.43,0.38,0.29,0.27),surface hydrophobicity were also significantly reduced(from 14.9 to 7.2,9.9,8.7,7.5,6.5);FT-IR analysis showed that glucosamine was imported into soybean protease in the form of covalent bonds again.(2)With the increase of hydrolysis degree,the solubility of M0,M0.5,M1.0,M1.5 and M2.0 increased significantly,which the solubility of M1.5 and M2.0 were better than that of soybean protein.Compared with soybean protein,the emulsifying activity of M0,M0.5,M1.0,M1.5 and M2.0 were improved in different degree,and the emulsifying activity of M0.5 was the highest in 7.31m2/g.The emulsification stability of M0,M0.5,M1.0,M1.5 and M2.0 were significantly higher than that of soybean protein(increased from 61%to 86,89,92,95,96%).The foaming of M0 was lower than that of soybean protein(reduced from 31.2%to 25.3%),but the foaming stability was higher than that of soybean protein(increased from 48.6 to 62.5%).The foaming of M0.5,M1.0,M1.5 and M2.0 were higher than that of soybean protein and M0,reaching 95,125,135 and 155%respectively,but the foam stability was lower than that of soybean protein and M0,which the foaming stability of M2.0 was 18.4%.Compared with soybean protein,the water holding capacity and the oil holding capacity of M0,M0.5,M1.0,M1.5 and M2.0 were significantly improved.The gel strength of gel prepared by M0 was higher than that of soybean protein,and the gel strength of gel prepared M0.5,M1.0,M1.5 and M2.0 was higher than that of soybean protein and M0,which the gel prepared by M1.0 had the highest gel strength.The vitro digestion of M0 was lower than soybean protein,M0.5,Mi1.0,M1.5 and M2.0 in vitro digestion ability were better than soybean protein and M0.(3)Response surface optimization preparation of high emulsifying soybean protein(MH),the best experimental conditions was sugar and soybean protein quality ratio of 0.96,hydrolysis degree 0.64%,reaction time of 3.29h.The results showed that MH and M0 emulsions could maintain good emulsification activity and stability under different pH,ion concentration and temperature conditions.After 21 days of storage,the lactation indexes of MH and M0 remained at 69.2%and 73.6%,while the lactation indexes of soybean protein were only 13.6%.Meanwhile,the oil yield of MH and M0 increased by 1.23 times and 1.11 times after 21 days of storage,while the oil yield of soybean protein increased by 1.78 times.During the 21 days of storage,the average particle size of MH and M0 emulsion remained at 65.5μm and 69.6μm,while the average particle size of soybean protein emulsion reached 124.8μm. |
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