The Research On Ovalbumin Glycation Under Microwave Field

Because of their high nutritional value and delicious taste, eggs (especiallychicken eggs) become one of the main foods for human beings. There were hugeamounts of eggs produced yearly in China, however, the lack of deep processingmake the urgent needed to find new ways to enhance the value of processed eggs.The appearance of egg white protein powder resolved the shortcomings of perishable,inconvenience in storage and transportation of eggs, what’s more, as it is convenientin using and excellent in functional properties (high gel property, high foamingproperty, emulsification, water retention), etc. it is widely applied in food processing.However, the egg white protein powder remains low in antioxidant activity, whilethe functional properties still has much room for growth, so as to improve itsapplication and value, it is needed to improve its antioxidant and functionalproperties.As one kind of chemical modification, glycosylation is the chemical reactionthat the carbohydrate combined with an amino group of protein molecules usingcovalent bond (including Maillard reaction). The glycosylation of protein viaMaillard reaction to modified protein is a technology that has great potential.Traditional Maillard glycosylation reaction by heating in a water bath, oil bath,heating mantle and ovens, etc., it is often required several hours to several weeks, thelong reaction time and high energy consumption make it needed to find a new safeand efficient heating method. In microwave heating, the electromagnetic energy istransferred and converted to heat through the motion of the molecules, which resultsin rapid and uniform heating of the materials throughout their volume. Compared tothe conventional thermal heating of materials proceeds via conduction andconvection of heat from the surfaces of the material, microwave heating requiresmuch shorter heating times and it is also a uniform heating.The study choose ovalbumin-glucose system as research object, its changes ofphysical and chemical properties in microwave field were researched, and the structure of reaction products were analysised, what’s more, the nutritional andsecurity of products were also evaluated. The aim of this study was providing atheoretical basis for the production of glycated ovalbumin in microwave field, andalso providing a new way for the utilization of egg products. The results of this paperare as follows:(1) The glycosylation reaction can quickly happen in ovalbumin-glucose systemin the microwave field, thereby rapidly increasing antioxidant activities (DPPHradical scavenging activity, reducing power, trolox equivalent antioxidant capacity)of ovalbumin, improving its functional properties (emulsifying property, foamingproperty) to a certain degree. The pH of the system decreased with the increase ofmicrowave power and heating time. The absorbance (A294nm, A420nm) of productsincreased with the increase of microwave power and heating time, the antioxidantactivities of Maillard reaction products (DPPH radical scavenging activity, reducingpower, trolox equivalent antioxidant capacity) and browning intensity (A420nm)have a good linear relationship.(2) The free amino group content of ovalbumin decreased with the increase ofmicrowave power, microwave heating time, heating temperature or conventionalheating time, thereby indicating that the extent of glycosylation increased. Underconventional heating, the content of melanoidin in Maillard reaction productsincreased slowly with the increase of heating time, and changed a little after reaction.However, it increased obviously under microwave heating with the increased ofheating time, especially after10min of microwave heating, the melanoidin wasdrasticly increased. SDS-polyacrylamide gel electrophoresis showed that theglycosylation reaction increased the molecular weight of ovalbumin. Underconventional heating, the protein aggregation will produce when the heatingtemperature and time reached to a certain degree, however, the aggregation producedeasily under microwave heating. The change of melanoidin content andSDS-polyacrylamide gel electrophoresis profile indicated that short time ofconventional heaing couldn’t make the ovalbumin Maillard reaction reached to theadvanced stage, however, short time of microwave heaing could make the ovalbuminMaillard reaction reached to the advanced stage. (3) The analysis of fluorescence spectra indicated that glycosylation reactionchanged the tertiary structure of ovalbumin, as the glycation extent under microwaveheating was higher than that under conventional heating, the change of structureunder microwave heating was more obvious than that under conventional heating.The analysis of circular dichroism spectra showed that the glycosylation changed thesecondary structure of ovalbumin, both the conventional heating and microwaveheating increased the α-helical content of ovalbumin, decreased the β-turn, β-sheetcontent of ovalbumin, In contrast to conventional heating, microwave heating alsoresulted in an elevated level of random coil. Fourier transform infrared spectroscopyspectrum indicated that there had sugar molecules combined with ovalbumin usingcovalent bonds. Environmental scanning electron microscopy images showed thatthe microstructure of system vary slightly under conventional heating, whilemicrowave heating make the microstructure changed significantly, the systemproduced porous surface, and there was a certain degree of aggregation occurred.(4) After ovalbumin glycosylation reaction, the allergenicity of proteindecreased, especially under microwave heating, the digestibility of protein increasedfirst and then decreased with the increase of glycation extent.