Mechanism Of Quercetin Inhibiting Methylglyoxal(MGO) In Maillard Reaction

Methylglyoxal(MGO)is the highly-reactive intermediate products produced in the Maillard reaction process.MGO further reacted with free amino groups of amino acids,peptides and proteins to form a series of irreversible and stable glycation end products,advanced glycation end products(AGEs).The accumulation of AGEs in vivo can arouse carbonyl stress,oxidative stress and tissue injury,and then induce some chronic dieases,including diabetes complications and cardiovascular and cerebrovascular diseases.This study constructed the quercetin and MGO reaction system and synthesized the intermediate products(MM-1)and final products(DM-2)during quercetin transformation.Furthermore,through the Lys-glucose-quercetin system,quercetin-MGO system,ovalbumin-glucose-quercetin system,this study also verified that the transformation of qucertein to quinones in Maillard reaction was attributed to its antioxidant efficacy,quercetin-MGO adducts MM-1 and DM-2 formed from trapping MGO remained has antioxidant and redox function which were still capable of inhibiting the formation of MGO/GO;qucertein-DM-2 also preserved the capacity to trap MGO and to form the adducts TM.Generally,this study uncovered various approaches to inhibit the formation of MGO/GO and AGEs,thereby improving flavonoid-sequestering mechanism of harmful glycation end products formed from Maillard reaction.The main investigations are as follows:1 Construction of quercetin and MGO reaction,synthesing and preparing MM-1 and DM-2 by Sephadex LH-20 and TLC chromatography,and the purity of MM-1 and DM-2 was more than 92%.In addition,the structures of MM-1 and DM-2 were identified using liquid chromatography-quadrupole-time of flight-mass spectrometry(HPLC-MS/MS),ultraviolet spectroscopy(UV)and nuclear magnetic resonance(NMR),the results shows that quercetin was conjugated with MGO at C-8 position to form MM-1,which embraced keto and enol isomers(MM-1A and MM-1B);when two molecules of MGO were located at C-6 and C-8 position of A ring of quercetin,there were four groups of keto enol enol isomers(DM-2A,DM-2B,DM-2C and DM-2D)in DM-2.2.Study on the biological activity of quercetin addition products(MM-1 and DM-2)according to standard quercetin.(1)Quercetin,MM-1 and DM-2 have good ability to scavenge free radicals;The reducibility of DM-2 and MM-1 at low concentration(<0.01 mmol/L)was higher than that of quercetin;In the contrast,the reducibility of quercetin was higher than that of MM-1 and DM-2 at high concentration(?0.01mmol/L);At room temperature the scavenging effect of DPPH radical,followed by quercetin,MM-1,DM-2;Under high temperature,the induction time of lard with or without quercetin,MM-1 and DM-2 was detected using Rancimat equipment model 743,which presented the antioxidation activity in descending sequence:quercetin,MM-1,DM-2.(2)Quercetin,MM-1 and DM-2 have the ability of scavenging free radicals.In the amino acids-glucose,ovalbumin-glucose system under food processing condition,When adding 100 mmol/L of quercetin,MM-1 and DM-2,three inhibitory rates of GO were above 46%,the inhibitory rates of MGO were slightly below 25%,the inhibitory rates of AGEs were over 75%.Under the bovine serum protein-glucose simulation physiological conditions,the inhibitory rate of GO was above 12%,the inhibitory rate of MGO was above 11%,and the inhibitory rate of AGEs was above 46%.The above results indicated that quercetin and MGO adducts can preserve functional activity of antioxidation,inhibitory efficacy of MGO/GO and AGEs in Maillard reaction under different conditions.3.Construction of Lys-glucose quercetin system:LC-MS/MS technique was used to monitor the changes of flavonoids,the formation of intermediate products and the subsequent changes of the intermediate products,and the quercetin-MGO system,ovalbumin-glucose-quercetin system demonstrated that:(1)In quercetin-Lys-glucose system,at the early stage of Lys-glucose reaction(5 min),quercetin hampered the production of MGO/GO mainly through the elimination of free radicals and was transformed into quinone compounds(QD-A and QD-B)via oxidative dehydrogenation;At the middle stage of the reaction(10 min),quercetin inhibited the formation of MGO by forming quercetin-MGO adducts(MM-1,MM-2);when the reaction continued by 30 min,The quercetin-sequestering of MGO pathways were diverted into:a.Through the capture of MGO,a variety of adduct products of quercetin-MGO(MM-1,MM-2),quercetin-2MGO(DM-1,DM-2,DM-3,DM-4);b.querce tin-3MGO(TM);c.quercetin-MGO adducts MM and DM underwent dehydrogenase via redox action and formed quinones(MMQ-1,MMQ-2,MMQ-3,DMQ-A1,DMQ-A2,DMQ-B,MGQ-1,MGQ-2).(2)Demonstrating the reaction mechanism of MM-1/DM-2:In the MM-1-MGO reaction system,after 5 min MM-1 could trap MGO and formed quercetin-2MGO adduct DM-1 and MMQ-1 quinone formed by oxidative dehydrogenation of MM.In the DM-2-MGO reaction system,there were three kinds of products deriving from DM-2 and MGO reaction:isomers of DM-2,quercetin-3MGO adducts TM-1 and TM-2 formed by further reaction between DM and MGO,dehydrogenation products of DM-quinone:DMQ-A2,DMQ-B2 and DMQ-A3.(3)In quercetin-ovalbumin-glucose system,the adducts of quercetin-MGO(MM)and quercetin-2MGO(DM),as well as the formation of quinone(MMQ-3)by the dehydrogenation of MM were detected.