Preparation And Formation Of Three Kinds Of Novel Vegetable Protein Gels

As an important food matrix, protein hydrogel has good texture properties and nutritional value. Investigate novel vegetable protein-based hydrogel and related products, not only enhance the level of processing technology and then expand its scope of application, but also have important scientific significance for the development of new protein-based biomaterials. In consideration of the process control difficulties and poor performance of traditional heat-induced protein gels, this thesis was focusing on the preparation and formation mechanism of enzyme-induced gels, heat-induced Self-assembly transparents gels, as well as the emulsion gels, based on the legume proteins as main raw materials. Specifically, the gelation properties of three Phaseolus legume protein isolate rich in 7S/8S globulin were investigated. The main research results are showed as follows:1. Enzyme-induced gels. The gelation process of three protein isolates from Phaseolus legumes (kidney, red and mung beans, further noted as KPI, RPI, MPI) and the properties of the corresponding gels, induced by microbial transglutaminase (MTGase), were investigated and compared with that of soy protein isolate (SPI). It was found that, even though MTGase treatment resulted in gelation for all protein isolates, the properties of the formed gels showed considerable variation. The mechanical strength of the gels made from RPI and MPI was much higher than that of a SPI gel. Heating and subsequent cooling treatment could greatly improve the mechanical strength of enzymatic-induced gels. Protein solubility tests indicated besides covalent corss-linkage, electrostatic forces, hydrophobic and H-bondings were the primary forces responsible for the formation of corresponding gels, the disulfide bonds also involved, but the extent is not obvious as SPI, because Phaseolus legumes protein isolates rich in 7S/8S globulin (vicilins), is devoid of disulfide bonds among individual subunits.2. Heat-induced self-assembly transparents gels. The heat aggregation and gelation of 7S/8S globulin storage proteins from red kidney bean, red bean, mung beans (further noted as KPG, RPG and MPG) in low pH and low ionic strength(30mM)was compared and investigated. The results shows that all the tested vicilins could form transparent gels if the protein concentration was high enough, or the heating time long enough. However, the minimum protein concentration needed to form the transparent gels was lowest for KPG, when heated for 10 h, the critical gelation concentration low to 1%. At the same protein concentration (5%, w/v), 80℃heated for 10 h, the mechanical moduli of the formed fibrillar gels considerably decreased in the order: KPG > MPG > RPG. Through Atomic Force Microscopy (AFM) visualized heat aggregates, indicated that all the tested vicilins formed fibrillar aggregates, and KPG have longer, shorter for RPG. The SDS-PAGE results also showed that the heating treatment led to marked degradation of all protein subunits.3. Emulsion gels. The gelation properties and microstructure of three different cold-set SPI emulsion gels, induced by GDL, CaCl2 and Transglutaminase (MTGase) were investigated and compared. The effects of different thermal treatment on various formed emulsion gels were also evaluated. The results shows that considerable differences in gelation properties were observed among the emulsion gels formed using various coagulants and initial emulsions. The heat-treated after the emulsification impeding the formation of enzymatic emulsion gels while facilitating the formation acid/salt gels to some extend. The textural properties and WHC of enzymatic emulsion gels were to a variable extent improved by the additional heating. The WHC of the emulsion gels seemed to be not directly related to their gel network strength. Confocal Laser Scanning Microscopy (CLSM) results shows that the CaCl2 induced emulsion gels was in a coarse structure; while MTGase and GDL induced gels has a filamentous network. By comparison, it can be concluded that the enzymatically induced gelation by MTGase is a most appropriate technique to form SPI-coated emulsion gels with excellent gel hardness and microstructure when using unheated SPI solution.