Study On Formation Of Nε-Carboxymethyllysine(CML) And Nε-Carboxyethyllysine(CEL) In Fructose-Lysine System

Advanced glycation end products(AGEs)generated from Maillard reaction between reducting sugar and proteins, have been proved to be associated with the development of longterm complications such as diabetes mellitus, aging, and cardiovascular diseases. Food processing conditions especially heating temperature can influence the formation of AGEs dramatically.The main purpose of our study is to investigate the formation conditions and kinetic of two well-characterized AGEs CML and CEL. A fructose-lysine system was heated at different molar ratios of fructose to lysine(0.25:1-4:1), different p H values(4.0-8.0), different temperatures(20-120 ℃) and different heating time(20-120 min). The contents of CML and CEL were determined by liquid chromatography-tandem mass spectrometry with stable-isotope dilution technique. Dynamic trends of reactants(fructose and lysine),main intermediates(GO and MGO) and CML and CEL in the system heated at different temperatures(70-120 ℃) for different time(0-60 min) were also researched.Simple kinetic models of CML and CEL formed in the system heated at 70-110 ℃ for 0-60 min were built.The main results are shown as follows.(1)The highest concentrations of CML and CEL were 4.26 μg/m L at the molar ratio of 1:1 and 5.39 μg/m L at the molar ratio of 4:1, respectively. They also increased with p H ranging from 4.0 to 8.0 in parallel with temperatures increasing from 20 to 120℃. The contents of CML and CEL reached the maximum 4.94 μg/m L and 3.34 μg/m L respectively after heating for 60 min at 100 ℃. Our research indicated that proper molar ratio of fructose to lysine, alkaline p H levels, higher temperature as well as certain heating time can accelerate the formation of CML and CEL.(2)The extent of fructose consuming in the system was higher than that of lysine which reached a no-loss period at later heating stages. The concentration of GO increased with increasing temperatures and longer heating time,while MGO concentration decreased when heated at higher temperature for long time.Both of CML and CEL concentrations increased with the increasing time at 70-110 ℃,while they were both decreased at 120 ℃ in longer heating time.(3) The formation of both CML and CEL in fructose-lysine system during heat treatments(70-110 ℃, 0-60min) basically fitted zero-order reactions,their rate constants in the range of 0.0073 to 0.1379 μgml-1min-1 with an activation energy of 86.11 k J/mol for CML and 85.97 k J/mol for CEL.