Formation And Influencing Factors Of Advanced Glycation End-products In Egg Products

Advanced glycation end-products are a series of complex and stable compounds produced from non-enzymatic reactions.AGEs could be formed from the Maillard reaction,through the reaction of the carbonyl group of reducing sugar with proteins or amino acids.AGEs could be also produced from several other pathways,such as the oxidation of reducing sugars,ascorbic acid and lipids.The amounts of AGEs in food are affected by the type of food,processing method,storage condition and other factors.To date,the majority of reported studies on dietary AGEs focused on meat,bakery and dairy products.There is a lack of information on AGEs in egg,an important food category in our daily life.In this study,the UPLC-MS/MS was applied to analyze two typical biomarkers of AGEs,namely,the N-?-carboxymethyllysine(CML)and the N-?-carboxyethyllysine(CEL),in egg white and yolk.The main objectives included:evaluated the biological variance in AGEs among individual raw eggs and subsequently heated eggs as well as the AGEs levels affected by the brand and the type(cage free vs.battery cage eggs)of eggs;investigated the changes of AGEs during storage,and the correlation between AGEs content and egg freshness;applied kinetics functions to develop a mathematical model for the effects of heating temperature and time on AGEs formation in egg whites.The detailed contents are as follows.1.Cage-free and battery cage hen eggs produced from two different companies were used in this study.UPLC-MS/MS was applied to determine the content of AGEs in egg white and yolk,including the raw and their mild heated(80?-6min)and severe heated(100?-30min)products.Results showed that A large biological variation in AGEs among individual raw eggs was found(e.g.,CEL in yolks 1.26–10.57 mg/kg,n=16).The yolk had higher levels of CML(125%more in average)and CEL(82%more in average)than the white for each raw egg,attributing to the higher protein levels and higher susceptibility of egg yolks to lipid oxidation.Heating led to significant increases(p<0.05)of CML in egg whites and yolks,but resulted in an average of 17–18%decrease of CEL in egg yolks.Whether eggs were cage-free or not had little effect on their CML and CEL levels,but raw and heated eggs from two different companies contained significantly different amounts of CML and CEL.Overall,egg whites are more susceptible to heating than egg yolks and severe thermal treatment should be avoided to reduce the contents of AGEs in egg whites.2.Hen eggs were collected from a local farm on the same day the eggs were laid by the birds,and a total of three batches of eggs were collected on separated days.The eggs were stored at room temperature(22?,RH 75%)for 0,8,16,24,and 32 days.The changes of HU value,p H and the AGEs content of raw eggs during the storage were analyzed.In addition,the effects of heat treatments on the amounts of AGEs in eggs stored for different time were evaluated.The results showed that the HU values of eggs continuously decreased from 79.1-94.1(0d)to 60.4-65.3(32d)during the storage.The p H of both egg whites and yolks gradually increased during storage,from 8.40-8.74 to 9.23 for egg whites,and from 6.20-6.22 to 6.61-6.71 for egg yolks.The content of CML was significantly increasedduring the storage(P<0.05),and was positively correlated with storage time.After 32d of storage,the CML level in raw egg white was increased 1.65 times as compared to the eggs without storage.The amount of CEL in egg white only increased by 11-61%during 32 d of storage,while the increased rate was somewhat fluctuated.However,there was no obvious change in the amount of CML in egg yolk during storage,but there was a slight decrease in the CEL level in the yolk,decreasing 6-30%after 32 d of storage,although not significantly different(P>0.05).After heating at 80?for 6min,the level of CML in egg whites increased by 44%(8 d)71%(16 d),157%(24 d),199%(32d).After the 100?-30min heat treatment,the amount of CML in white increased by 9%(8 d),10%(16 d)78%(24 d),and 145%(32 d),respectively.This indicated the levels of CML/CEL in heated whites were positively correlated with the storage time of the eggs prior to heat treatments.However,there was no significant change for the CEL in egg whites and both CML and CEL in egg yolks.In addition,CML in the white showed a good linear relationship with the length of the storage time,HU value and p H for the eggs from all three batches,while CEL in the white and CML/CEL in the yolk showed no obvious linear correlation or showed somewhat linear correlation for only one or two batches of eggs.3.The levels of AGEs in egg whites were more severely affected by heating and storage compared to that in egg yolks.Therefore,in this study,the white was selected to evaluate the changes of its AGEs levels as affected by heat treatments at 80?,100?and 121?for up to 60 min.After being heated for 60min,the CML increased from 1.14±0.09 mg/kg to 4.62±0.06 mg/kg(80?),12.34±4.18mg/kg(100?),and 100.06±1.57 mg/kg(121?),respectively,indicating the great impact of thermal treatment on the CML level in the white.The increase of CEL level was minor due to the heat treatments at 80?and 100?,increasing from 2.36±0.15 mg/kg to 2.96±0.21 mg/kg and 4.18±0.24 mg/kg,respectively after 60 min of heating.However,heating at 121?for 60 min resulted in the CEL content up to 40.27±1.58 mg/kg,which was 12.6 times and 8.6 times higher than that of heated at 80?and 100?.There was a good linear relationship between CML and CEL in egg whites(R~2=0.9882),indicating that underlying pathways for the CML and CEL formation were highly correlated.Based upon the results from kinetic analysis,the formation of both CML and CEL conformed with the zero-order reaction(R~2=0.7307-0.9855).The Arrhenius equation was used to infer that the reaction activation energy for CML was 100.89KJ/mol,and that for CEL was 122.39KJ/mol,indicating that the reaction energy level of CML in the white was lower than that of CEL,and thus the formation of CML was more likely to occur.The biological variance in the levels of CML and CEL in raw or heated whites and yolks as well as the effects of the type and the brand of eggs on their AGEs levels had been investigate through this study.In addition,the effects of storage on the AGEs levels in raw and subsequently heated eggs had been evaluated,and kinetic models had been developed for the formation of CML and CEL in egg whites during heating.The study provide a theoretical basis to help limit the formation of AGEs in egg products during processing and reduce the relevant food safety risk.