| Oat protein isolate(OPI) has been gaining more attentions these years due to its unique nutritional properties and physiological activities, balanced amino acids composition, wide sources, etc. However, there are relatively few studies of oat protein and its functional properties. The use of oat protein as an ingredient in food industry is also limited. Therefore, we mainly investigated the glycation reaction and emulsifying properties of oat protein isolate, and the physical and chemical properties, the function and structure of the conjugates were systematically studied. The aim of this study was to improve functional properties of OPI and broaden their application, which could further provide theoretical knowledge for the comprehensive development and utilization of oat protein.Firstly, this study investigated the effects of different saccharides(Xylose, Glucose, Lactose, Dextran 20 k D and Dextran 40 k D) and the extent of glycation reaction on the functional properties of oat protein. The solubility, emulsifying property, graft degree and browning degree of OPI-saccharide complexes during glycosylation were measured under the condition of 90℃, p H 9.0. The result showed that the extent of glycation was evaluated by the measurement of graft degree, extent of browning and p H, which indicated Xylose was the most reactive sugar with OPI, followed by Glucose, Lactose, Dextran 20 k D and Dextran 40 k D. The covalent attachment of different sugars to OPI was fully confirmed by SDS-PAGE with both protein and carbohydrate staining. OPI-glucose conjugates exhibited higher solubility as compared to the unmodified OPI and other conjugates. OPI-polysaccharide conjugates, especially for Dextran 40 k D, demonstrated the most improvement in the emulsifying property.Secondly, the effects of reaction temperature(80℃、90℃ and 100℃) and mass ratio of OPI to dextran 40 k D(2:1、1:1 and 1:2) on the functional properties of OPI-dextran conjugates were investigated on the base of above results. Taking several important parameters into consideration, we measured the emulsifying properties and solubility, and combined the graft degree, extent of browning and p H changes on the system. The optimal reaction conditions were obtained as follows:OPI reacted with dextran 40 k D at 90℃,p H 9.0, mass ratio 1:1, and the reaction time was around 60 min. The conjugates prepared under this conditions showed excellent emulsifying properties and solubility.Thirdly, the physic-chemical characteristics and structure features of OPI-dextran 40 k D conjugates were analyzed by fluorescence analysis, surface hydrophobicity, HPLC, FTIR, CD and so on. The results confirmed that the glycation reaction was occurred. Emulsifying properties and solubility, thermal stability of graft product increased, and the surface hydrophobicity decreased with increasing of reaction time. HPLC, FTIR and CD showed that due to the covalent attachment of dextran to OPI, the molecular weight of OPI-dextran 40 k D conjugates became higher, the protein secondary, tertiary structure changed, α-helix content decreased. It is also indicated that the physic-chemical characteristics of proteins are essentially determined by their structure features.Finally, emulsifying properties of O/W emulsions stabilized by native OPI, OPI-dextran 40 k D conjugates and heated OPI were characterized by zeta-potential, mean droplet size and microstructure. The results showed that OPI-dextran 40 k D conjugates were capable of forming a finer emulsion, which exhibited smaller average particle size and better storage stability under different homogenization pressures(30, 60, 90 MPa) compared with other samples. When assessed in different p H and ionic strength, emulsions stabilized by OPI-dextran 40 k D conjugates resulted in improved emulsion stability to environmental stresses. CLSM depicted more uniform and smaller oil droplets that had a reduced tendency to coalesce for emulsions prepared with OPI-dextran 40 k D conjugates. |
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