Antioxidant activity of sugar–lysine Maillard reaction products in cell free and cell culture systems

Model Maillard reaction (MR) products (MRPs) employing lysine with an aldohexose (e.g., glucose), ketohexose (e.g., fructose), and aldopentose (e.g., ribose) sugars were generated (e.g., pH 9.0; over 2 h heating at 120°) and fractionated with ethanol into low (LMW) and high (HMW) molecular weight fractions. Characteristically different temporal patterns of fluorescence and ultraviolet/visible absorption spectra were obtained from the three distinct sugar–lysine MRPs, and corresponded to different yields of total and dialyzable carbon, indicating that relative reaction rates and degree of polymerization favored the Rib–Lys MRP, compared to Glu–Lys and Fru–Lys MRPs, respectively (p < 0.05). Further characterization of antioxidant activity of the sugar specific-lysine MRPs in chemical (e.g., hydrophobic (1,1,-diphenyl-2-picryl-hydrazyl radical (DPPH) and hydrophilic (Fenton reaction-induced hydroxyl radical) in vitro scavenging assays showed that Rib–Lys HMW MRPs had the highest (p < 0.05) affinity to scavenge free radicals. All sugar–Lys MRPs, however, displayed similar protection of cultured Caco-2 cells from exposure to H2O2-, 2,2′-azobis-(2-amidinopropane) dihydrochloride (AAPH)-, ferrous (Fe2+)-, and cupric (Cu2+)-induced cytotoxicity, evaluated both from redox (e.g., MTT response) and cell membrane integrity (e.g., LDH secretion). HMW-MRPs exhibited stronger (p < 0.05) antioxidant activity to scavenge hydroxyl and DPPH radicals, and a greater (p < 0.05) protective effect against both Fe2+- and Cu2+-induced cytotoxicity in Caco-2 cells than corresponding LMW-MRPs. We conclude that HMW MRPs possess affective antioxidant protection against oxidizable substrates; however, the degree of polymerization of this product, characteristic to the source of monosaccharide used in the reaction, is not a distinguishable factor for this bioactivity.