Enzymatic Preparation Of Soy Protein-oligochitosan Polymer And Its Properties

Nutritious soy protein is a high- quality plant protein, but some of its functional properties cannot well meet the needs of food processing. In this study, soy protein is enzymatically modified by acyl-transfer reaction catalyzed by transglutaminase, which catalyzes aminoacyl transfer reaction between γ- carboxamide of glutamine residues in proteins and free amino group of chitosan oligosaccharide and makes soy protein crosslinking with oligochitosan. Through this method, the functional properties of soy protein are partly improved. This study uses enzymatic reaction to improve some functional properties of soy protein, carry out preliminary research for preparation conditions of enzymatic polymer and research their functional properties and structural changes, aiming to develop and research food materials for functional food as well as provide a theoretical reference for studying of functional properties of soy protein.Firstly, the optimization of preparation conditions of enzymatic polymer is researched. The influence of sugar / protein ratio, soy protein concentration, reaction time. for the enzymatic reaction are discussed by single factor experiments. Degree of polymer graftation is used as the index to determine that the optimal reaction conditions are at 37℃,TGase 10U/g protein, sugar / protein ratio at 0.8, soy protein concentration at 6 mg / mL, reaction time at 3h, and the degree of polymer graftation is 57.49%.The changes of polymer structure can be seen from the fluorescence spectra. The maximum fluorescence intensity of the polymer is obtain when excited at 286 nm and emissioned at 340 nm.There is a small. Wavelength shift can be seen after comparing with wavelengths of soy protein, but the offset is small. The electrophoresis results reflects that after the enzymatic reaction, some subunits bands of soy protein has disappeared or decreased, macromolecules has generated; The molecular weights of the polymer changes significantly in comparison with the molecular weights of the protein molecule; The glycosyl bands can be seen clearly by electrophoresis PAS staining, which proves that enzymatic polymer has been formed. The gel structure of this enzymatic polymer changes significantly, which shows that the heat-induced gel has cluster structure and mesh structure; The gel micelle of polymer increases and gathers gradually, which forms more compact gel.Functional properties of the obtained polymer are studied. The results show that the functional properties of soybean protein are partially improved after enzymatic modification. Compared to the properties of soy protein, gelation, emulsion stability, Thermal stability and foaming stability are significantly improved; Emulsifying activity, foaming, solubility and polymer-surface’s hydrophobicity are slightly reduced; The gelation properties of the polymer is obviously improved, hardness, elasticity, water-holding capacity and intensity of acidification gel increased 54.15%、16.56%、17.20%、10.62%, respectively; compared with soy protein; Because of the oligochitosan, hardness, viscosity, water-holding capacity and intensity of heat-induced gel are obviously decreased.