| Casein performs many remarkble functions in foods. It contributes to the structural and textural properties of foods. But any protein could not exhibit all desirable functional properties, so modification plays an essential role in conferring the food proteins some special properties. The Maillard reaction(MR) or nonenzymatic glycation was a spontaneous reaction between amino acids and amino groups of peptides or proteins and reducing saccharides. MR was one of the major protein modifying reactions and an effective and simple method to improve functional properties. Highly glycated proteins produced by such reactions gave rise to fewer safety issues than chemically modi?ed proteins. However, there were some shortcomings for MR, such as poor efficiency, long reaction time and high energy consumption. On the other hand, microwave was a new processing technology and had diverse applications in many ?elds. Microwave was environmentally friendly and, moreover, had the potential to develop new products with aunique functionality.In this project, casein, glucose and cyclodextrin were used as main materials, and casein-saccharide grafts were synthesized by the microwave assistance.The main analytic methods, conditions, the mechanism of reaction, and the physicochemical characteristics,conformation and functional properties of grafts were studied systematacially at the molecular level in order to research casein-saccharide modification,find functional properties of products by combining thermodynamics with modern spectroscopic analysis.Through these studies, the new and effectively reactive ways and a clearly mechanism how it worked were obtained.Then it can play great role to improve the functional properties of protein,solve the problems of glycosylation slowly, security risks in enzyme-catalyzed reactions as well as poor functional properties of grafts. For the future development of a particular product of casein with a specific feature, and studying of protein function by microwave, catalyzed glycosylation reaction, this study can provide important theoretical guidance and technical support.In this study, effect of microwave time and microwave power on Maillard reaction of casein-glucose system, the results showed that browning and degree of graft increased with microwave time and power extending, then after microwave power 500 W and 20 min, the increase rate of grafting degree decrease, comprehensive browning degree, subsequent test selected microwave power 500 W and 20 min. The order of the grafting reaction of casein and reducing sugar by microwave heating was the βcyclodextrin>glucose > lactose > isomaltooligosaccharide.Endogenous fluorescence spectrum and ultraviolet spectrum analysis showed that the casein treated by microwave heating ultraviolet absorption value is higher than that of water bath and untreated casein in 220-238 nm and 260-340- nm,. The endogenous fluorescence absorption peak occurred red shift phenomenon in casein treated by microwave heating. Microwave heating can stability promote casein with glucose glycosylation, such a phenomenon has not happened forβ cyclodextrin. Influence of water bath heating and microwave heating to the intermediate was not significantly different. Microwave heating as time extended gradually, color of reaction solution contain casein and glucose, beta cyclodextrin color gradually increased. Browning degree(A420) obviously increased, significantly higher than that of water bath heating of the sample. The disulfide bond content had significantly changes between microwave heating and water bath heating. The electrophoresis banding of glycosylation casein is similar betweeen water bath heating 60 minutes and microwave heating 30 min, indirectly shows that microwave heating glycosylation reaction can shorten the time and cost savings.The results of the features experimental showed that when microwave power is 500 W, microwave heating for 20 min, the gel strength of glycated casein is 134 g which is 1.19 folds of that glycated casein treated by water bath heating. Casein, water bath heating glycated casein and microwave heating(500 W, 20 min) glycated casein exhibited higher water binding capacity in turn(5.08, 13.13 and 17.1 g.g- 1 protein). However, the oil binding capacity decreased in turn(4.88, 3.22 and 3.58 m L. 1 g protein). Gel microstructure analysis showed that gel network structure of glycated casein by microwave heating treatment became rules, dense. So gel hardness and water binding capacity were better than that of casein. Apparent viscosity of the aqueous dispersions of glycated casein by microwave heating treatment is highest between casein and glycated casein by water bath heating treatment. During 0 to 6 months of storage, gel hardness of casein and glycated casein decreased, but the change is not obvious.Microwave treatment can significantly improve the foaming ability and foam stability of casein. Effect of microwave treatment on maillard reduction ability was obvious(P < 0.05). Glycated casein after microwave heating(500 W, 20 min) and the water bath heating, its reducing power were 0.59 and 0.57, significantly higher than that casein without glycosylation(P < 0.05). When microwave processing 20 min, with the increase of microwave power, the inhibition rate of glycated casein gradually increased, when the microwave power increased to 500 W, the inhibition rate of glycated casein can reach 73.1%, significantly higher than that of casein without glycosylation(63.42%)(P < 0.05). When microwave power increased to 500 W, the scavenging effect of casein glycated β-cyclodextrin by microwave heating increased from 6.97% to 14.94%, significantly higher than that of untreated casein(5.53%)(P < 0.05). The scavenging effect of casein glycated β-cyclodextrin by water bath heating increased by 4.07% compared to untreated casein. When microwave power increased to 500 W, microwave treatment can significantly improve EAI and ESI. It is not only related with the modified casein, may also related to effect of the microwave radiation on the structure of the casein.The fluorescence intensity of glycated casein was higher than that of casein without glycosylation, and the fluorescence intensity of glycated casein treated by microwave heating was higher than that of glycated casein with water bath heating, and this indicated that more and more advanced maillard reaction products generated by microwave heating. Fluorescence intensity increasing illustrated that the end products of Maillard reaction increased, it also can be confirmed by browning results. After glycosylation, the content of random curl reduced, β corner increased, especially the content of β corner increased more after glycosylation reaction by microwave heating. All structural changes showed that glycosylation had no significant influence on the secondary structure of casein. After glycosylation, both denaturation temperature and denaturation enthalpy dropped, glycated casein treated by microwave heating decreased more. |
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