Effect Of Tea Polyphenols On Antioxidant Activity Of Maillard Reaction Products

Maillard reaction is a non-enzymatic browning reaction between carbonyl compounds and amino compounds.Although the specific mechanism of the Maillard reaction is not yet clear,and harmful derivatives are also produced,many studies have shown that the Maillard reaction products have strong antioxidant activity.Using sugar-amino acids(proteins)as the Maillard model,this study studied the effects of tea polyphenols on Maillard reaction products.At the same time,the effects of tea polyphenols on the properties of the protein after the reaction were discussed,so as to provide theoretical basis for the regulation of antioxidation of Maillard reaction products participated by polyphenols.Firstly,different Maillard models were constructed by different sugars(glucose,maltose,lactose,sucrose and fructose)and different amino acids(glycine,lysine,glutamate,cysteine,phenylalanine and alanine).The effects of tea polyphenols on the in vitro antioxidant activity of different Maillard models were investigated using DPPH,ABTS,total reducing capacity and hydroxyl radicals.The results showed:In the DPPH method,ABTS method and the total reduction capacity determination,the antioxidant activity of different Maillard model products increased firstly and then slowly with the increase of tea polyphenols.Compared with other models,the glucose-cysteine(Glc-Cys)model products itself had strong antioxidant capacity.The DPPH clearance rate,ABTS clearance rate and total reduction capacity are 64.36%,99.85%and 2.444,respectively,which were significantly higher than other models and control V_C(P<0.05).The hydroxyl radical scavenging rate of each model was between 50%and 80%,and tea polyphenols had no significant effect on its antioxidant activity(P>0.05).The Glc-Cys model has the highest hydroxyl free clearance rate.With the increased of tea polyphenol content,the fluorescence intensity of Glc-Cys reaction products at excitation wavelength decreased gradually,while the fluorescence intensity at emission wavelength increased first and then decreased.Tea polyphenols reacted with substrates and products in the Glc-Cys reaction system to produced new substances and affectd antioxidant activity.Secondly,according to the antioxidant results,Glc-Cys was selected as the reaction model,and the effect of tea polyphenols and its main component gallocatechin gallate(EGCG)on the p H value,intermediate products and Browning degree of the system during the Maillard reaction were investigated under different reaction conditions.The results showed that:the addition of polyphenols resulted in the p H value of the system decreased,the intermediate products increased and the browning degree increased.In addition,with the increase of the reaction time and the increase of the reaction temperature,the p H value of the reaction system gradually decreased and the intermediate products gradually increased.The Browning degree would be reduced if the temperature was too high(130?)or too low(110?).The results of Glc-Cys(all 0.1 mmol)model antioxidant experiment showed that when the EGCG dosage was 1.5 mg,heating time was 1 h,temperature was 130?,p H was6,and the molar ratio of carbonyl to ammonia was 1.5:1,the antioxidant capacity of the reaction products was the strongest.The components of the reaction products of the Glc-Cys-EGCG system were analyzed by liquid chromatography-mass spectrometry.The results showed that there were self-condensates of cysteine,condensates of glucose and cysteine,cysteine-EGCG conjugates and unreacted EGCG in the products.Finally,the effects of tea polyphenols on the antioxidation of Maillard model products constructed by three common proteins(gluten protein,soybean protein,peanut protein)and glucose were studied.The results showed that the products with higher temperature had higher antioxidant capacity.Taking the glucose-gluten protein model as an example,the DPPH clearance rate,ABTS clearance rate and total reducing capacity of the products with glucose-gluten model at 70°C were respectively 18.28%,53.30%and 0.095.At 130?,the measurement results were 42.72%,67.23%and 0.206,respectively.High temperature significantly(P<0.05)improved the antioxidant activity of model products.At the same temperature,with the increase of tea polyphenols,the antioxidant capacity of three protein Maillard model products increased.In addition,with the increase of tea polyphenol content,the fluorescence intensity of the three proteins decreased,but the hydrophobicity and UV absorption value increased.Tea polyphenols caused the changes of protein secondary structure:the content of?-sheet of gluten protein decreased,the content of?-helix,?-turn and irregular coil increased;the content of?-sheet of soybean protein increased,the content of?-helix decreased;the content of?-helix and irregular coil of peanut protein increased.Tea polyphenols changed the foaming and emulsifying properties of protein:with the increase of tea polyphenol content,the foaming and emulsifying stability of gluten,the foam stability and emulsification of soy protein,the emulsifying stability of peanut protein were all increased,the emulsification of peanut gluten and the foaming ability of peanut protein were all decreased,while the foam stability and emulsification of peanut protein showed a trend of first increased and then decreased.Tea polyphenols had no significant effect on foam stability,foaming properties and emulsifying stability of gluten protein(P>0.05).The volatile components of the Maillard products of glucose-gluten protein included 39compounds,such as furans,ketones,aldehydes,alcohols,ethers,lipids and aromatics.The addition of tea polyphenols increased the number of these types of substances to 42 and also reduced the original content of volatile components in the products(except for the three lipid substances).