Effects of C-Ring Structural Differences on the Inhibition of Nε-(Carboxyethyl)lysine in the Methylglyoxal-Lysine System by Flavonoids

This study investigated the effects of taxifolin (Tax), quercetin (Que), (+)-catechin (Cat) and luteolin (Lute) on the advanced Maillard reaction stage in the methylglyoxal-lysine (MGO-Lys) system. Since the four flavonoids share identical <i>A</i>- and <i>B</i>-ring structures, the inhibitory effects and molecular mechanisms of flavonoids with different <i>C</i>-ring structures on <i>N^ε</i>-(carboxyethyl)lysine (CEL) formation were revealed. The results demonstrated that Cat exhibited the best inhibitory effect on CEL with an inhibition rate of 53.78%, while Lute showed the lowest inhibition rate of 3.97%. The flavonoids (i.e., Tax, Que, Cat and Lute) inhibited the formation of non-fluorescent CEL, where hydroxylation at C³ on the <i>C</i>-ring favored the enhancement of the inhibitory effect of the flavonoids on CEL, while the C²-C³ double bond and the carbonyl group at the C⁴ position reduced their inhibitory ability. The alkaline environment favored the enhancement of the inhibition of CEL by Tax, Que, Cat and Lute. Notably, Tax, Que, Cat and Lute can inhibit CEL formation by competitively capturing MGO to form mono- or di-adducts and reducing lysine consumption. This study provides innovative strategies and a theoretical foundation for developing effective CEL inhibitors in food thermal processing.