Epicatechin and epigallocatechin gallate inhibit formation of intermediary radicals during heating of lysine and glucose

High concentrations of the tea catechins epicatechin (EC) or epigallocatechin gallate (EGCG) inhibited formation of highly reactive intermediary radicals appearing during the Maillard reactions (MR), that take place during heating glucose and lysine at 70 degrees C in EtOH/HEPES buffer at pH 7.0 and pH 8.0. Radicals were trapped by ethanol, which subsequently were converted into spin adducts of the spin trap alpha-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN). EGCG was found to be more efficient than EC as inhibitor of intermediary radicals during the MR. Based on UV/Vis-spectroscopy, measurement of oxygen consumption and LC-MS detection of intermediates, it is suggested that the quinone form of autoxidised EC reacts with lysine through either a Michael type addition or a "Strecker like" reaction and thereby influences the formation of intermediary MR products as well as radicals. (C) 2013 Elsevier Ltd. All rights reserved.