Regulation Of Milk Protein Glycation Products

In the process of processing,storage and transportation of dairy products,amino acis and proteins in dairy may react with reducing lactose cause non-enzymatic glycation reaction.In free amino acids and free residues in amino acids of proteins,except N-teminal amino group,the amino and guanidine groups in the side chain of Lys and Arg will produce a crosslinking reaction with 1,2-dicarbony compounds.1,2-dicarbony compounds,such as methylglyoxal(MGO)and glyoxal(GO),are intermediates glycation products,which has high reactive,advanced glycation end products(AGEs)is further induced by them.The glycation reaction will not only affect the quality of dairy products by changing the structure and causing cross-link of casein,but increase the dairy security risks and threat to human health with the exogenous AGEs produced in the processing and storage peocess of dairy.The study found that the site species of casein glycation are mainly in Lys and Arg residues.Therefore,the paper make Lys and Arg as a starting point,on the basis of studying the effectors of generating MGO and GO,kinetic of MGO and GO,the influences of formation fluorescent AGEs in Lys/Arg-reducing sugar model systems,further explore the influence factor of casein glycation and the impact of glycation on casein.At the same time,geistein is selected as a glycation inhibitor to inhibit the glycation intermediates(MGO&GO)and fluorescent AGEs.The main contents and conclusions in this dissertation were summarized as follows:1.Lys-reducing sugar and Arg-rducing sugar models are established,respectively,the formation of MGO and GO in these models is detected by gas chromatography(GC).The influence factors of generating MGO and GO in these models are studied,such as the type of amino acid,the type of reducing sugar,temperature,time,pH and glycation inhibitor(genistein).The reaction rate and apparent activation energy in the kinetic of MGO and GO in different temperatures(100;121;135;150 and 180?)are investigated.And the generating content of MGO and GO was also investigated before and after the genistein involved in.The results showed that the reaction time is in the first place to affect the formation of MGO and GO in Lys/Arg-reducing sugar models,followed by temperature and pH.In dynamics,the reaction rate of MGO is faster than GO and the apparent activation energy of MGO is lower than GO,which indicated that MGO is easier to generate than GO in heating process.Moreover,MGO and GO is easier to generate in Lys models than that in Arg models.In addition,geistein can inhibit the formation of MGO and GO.2.Lys-reducing sugar and Arg-reducing sugar models are established,respectively,the influence factors of generating fluorescent AGEs in these models are detected in fluorescence wavelength(?ex/?em=340 nm/465 nm),such as the type of amino acid,the type of reducing sugar,temperature,time,pH,motel ion and glycation inhibitor(genistein).The results showed that the reaction time is the most important factor in the formation of fluorescent AGEs in Lys/Arg-reducing sugar models,followed by glycation inhibitor(genistein),reducing sugar concentration and temperature.Other factors,like the type of amino acid,the type of reducing sugar,pH and motel ion,showed little effect on generating fluorescent AGEs and there is almost no difference among them.3.Casein-lactose model is established,the formation of MGO and GO in the model is detected by gas chromatography(GC).The influence factors of generating fluorescent AGEs in the establishment of casein-lactose,casein-MGO and casein-GO models are detected in fluorescence wavelength,such as the type of amino acid,the type of reducing sugar(including MGO and GO),temperature,time,pH,motel ion and glycation inhibitor(genistein).Ultraviolet spectrophotometry(UV)and denaturing polyacrylamide gel electrophoresis(SDS-PAGE)are used to detect the impact of structure on casein glycation.The results showed that MGO and GO generated in 5 min in 121? in casein-lactose model,and the amount of MGO is higher than GO.The type of reducing sugar(including MGO and GO)is the most important factor in the formation of fluorescent AGEs in casein-sugar models,followed by reaction time.Other factors showed little effect,but the interaction factors,like "reducing sugar " time " and "temperature*time" showed obvious effect.UV and SDS-PAGE can effectively characterize the casein glycation induced by lactose,MGO and GO,which,the inhibitor of genistein on casein glycation is also characterize by SDS-PAGE.