| Soybean is rich in protein and other nutritional factors,including isoflavones,oligosaccharide,saponins and plhospholipids.Therefore,soybean and its products are very popular with many consumers because of the functional properties of improving the physical health and enhancing the body resistance to disease.However,soybean is also regarded as one of eight kinds of food allergens recognized by FAO.7S globulin protein in soybean accounts to 43%of total protein,and it contains three major allergens of soybean,such as Gly m Bd 28K,Gly m Bd 30K and Gly m Bd 60K.Nowadays,physical processing is used widely in food production by heating,high pressure,shear force and so on,and its aims to promote food processing efficiency and reduce the harmful factors in foods.Only a few applications of ultrasonic in food allergenicity reduction have been reported in literature.Based on the above reasons,the influence of ultrasonic assisted deglycosylation on structure and allergenicity of 7S globulin were investigated,and several works are involved in this study including structural characterization of 7S globulin treated by ultrasonic,assessment of in vitro digestion,antigenicity and allergenicity,and the effects of ultrasonic asisted enzymatic deglycosylation on structure and immunoreactivity and physicochemical properties of soybean 7S protein.The main results and conclusions are addressed as follows:1.Soybean 7S globulin was processed by ultrasonic in different time under same conditions(40 kHz,300W),and its primary structure and surface hydrophobicity did not change.Significant changes in secondary structure of processed 7S globulin were observed in which the content of a-helix increased by 14%,and content of ?-sheet and random coli decreased by 6-9%.The content of free sulfydryl increased firstly and then decreased,and the content of total sulfydryl remained constant,but it increased dramatically when the ultrasonic time exceeds 100 min.2.7S globulin treated with ultrasonic had a resistance to saliva and gastric digestion,but it was remarkably digested by duodenal juice.Antigenicity of samples which processed with digestion decreased firstly and increased subsequently,but allergenicity instead.The strongest of IgE-binding was observed when 7S globulin treated with ultrasonic at 40 min,and the weakest of IgE-binding was presented at 80 min.3.Under the conditions of ultrasonic assisted the enzymatic deglycosylation,?-conglycinin and Gly m Bd 30K(P34)in 7S globulin showed slightly lower molecular weight and consequently higher electrophoretic mobility compared with the native sample.The UV spectrum of processed samples showed blue shift and absorbance decreased.As shown from CD spectrum,a-helix and coils were transformed into ?-sheet after 7S globulin was deglycosylated.The fluorescent spectrum of processed 7S fraction showed a significant blue shift which implied the increased of surface hydrophobicity was increased.The contents of tyrosine and tryptophan decreased,but the contents of phenylalanine increased.Single deglycosylated 7S globulin exhibited the lowest of IgG-binding and IgE-binding,while enzymatic deglycosylation following ultrasound pretreatment enhanced the allergenicity.7S globulin is composed of 17 kinds of amino acids,and 8 varieties of essential amino acid for human need accout for 33.48%.The surface of native 7S globulin was covered with negative charge,and the charge was significantly reduced after enzymatic deglycosylation.The surface morphology of 7S globulin was fractal pattern and disorderly structure,and there were a few tiny particles on glycoprotein after enzymatic deglycosylation.The emulsifying ability and emulsion stability property remarkably observably had a reduction after enzymatic deglycosylation. |
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