The Effects Of Limited Glutamyl-endopeptidase Modification On Functional Properties Of Soy Protein

Soybean protein is a kind of plant protein resource with excellent quality andvariously functional properties, which is widely used in different kinds offood.β-conglycinin and glycinin is the major storage protein of soy protein,accounting for more than70%in the soluble soybean protein. There are extensionarea and core area in α,α′subunit, but only core area in β subunit of β-conglycinin.The extension area and core area have different effects on the functional properties ofsoy protein. Glycinin is composed of alkaline and acidic subunit. As the role ofstorage protein, they are both lack of the hydrophobic cavity to carry small molecules.Presently, modification of soy protein is carried out on the subunit protein level as anew trend. Glutamyl endopeptidase (GE, EC3.4.21.19) is specifically hydrolyzepeptide bond at alpha carboxyl formed of glutamate and (or) aspartate residue atprotein polypeptide C-terminal. GE can separate the extention area and core area ofβ-conglycinin, and make a hydrophobic modification on soybean protein as a resultof its special effect. This paper studied the binding between glycinin and Monascuspigment, and changes of emulsifying property and heating gelation property ofβ-conglycinin after GE limited hydrolysis. The aim of this paper was to find out thefood application of glutamyl endopeptidase and effect of β-conglycinin extension core.Main conclusions are as follows:(1) With GE limited hydrolysis, particle size, zeta-potential, surfacehydrophobicity of glycinin increased with the degree of hydrolysis increased. Thebinding constants of glycinin(hydrolysis degree=1.5%) and Monascus pigment wasreached to the maximum with a binding capacity of215U/g pro. After24h lighting,the color value of the protein-pigment complexes had a retention rate of90%.Binding with hydrolyzed glycinin, the photo stability of natural Monascus pigmentwas improved.(2) Comparing the emulsion properties of β-conglycinin,7S hydrolysis(7S-GE)and7S core, at different pH, ionic strength, heating and storage conditions.7S-GEemulsion presented similar properties with β-conglycinin emulsion. The particle size of7S core emulsion increased significantly. At the same time, its emulsifying activitydecreased dramatically and showed higher sensitivity to ionic strength. In addition,both the uniformity, stability of emulsion7S core droplets are inferior toβ-conglycinin or7S-GE emulsion. In conclusion, the hydrophilic7S extension areaaffects the emulsifying capacity and emulsion stability of soy protein.(3) Comparing the heat-induced gel properties of β-conglycinin and7S-GE.7S-GE gels had white appearance, more soft texture. Its gel strength decreased,becoming more easily to be destroyed. The network structure of7S-GE gels wasrough, uneven, and full of spherical aggregates, lacking of cross-linking in network.As a result, water holding capacity of7S-GE gels decreased significantly and showedfor higher sensitivity to iron strenths.7S extension area is conducive to the soybeanprotein gel hardness, orderly network, strong gel strength, anti to salt and high waterholding capacity.