Metal chelating and oxidative behaviour of maillard reaction products extracted from model and food systems
Creators: name: Wijewickreme, Arosha Nilmini
Publisher: name: University of British Columbia
Year: 2009

description: The elementary composition, metal chelating, oxidative behaviour and related genotoxic, and cytotoxic activities of different Maillard reaction products (MRPs), derived from both model and coffee systems were studied in vitro in the presence, or absence, of polyvalent metal ions. Non-dialysable model MRPs were synthesized by heating D-Glucose (Glu) or D-Fructose (Fru) with L-Lysine (Lys) under variable time-temperature, initial pH and initial water activity (a[sub w]) combinations. MRPs were also extracted from instant, brewed, and boiled roasted ground coffee powders to represent a food system. Elementary composition of Fru-Lys MRPs constantly exhibited a higher percentage of nitrogen and a relatively smaller number of Cu²⁺ binding sites compared to similarly derived Glu- Lys MRPs. Both MRP types exhibited only antioxidant activities in a metal free linoleic acid emulsion, but a combination of distinct anti-/prooxidant activity was observed in Cu²⁺ supplemented lipid emulsions with oxygen electrode. The two Glu-Lys MRPs derived from synthesis experimental conditions 3 and 13 (i.e., time, temp., pH, a[sub w]: 119 min, 127 °C, 6.14, 0.74 ; 71 min, 129 °C, 8.41, 0.78) and the two Fru-Lys MRPs derived from synthesis experimental conditions 5 and 11 (107 min, 157 °C, 8.51, 0.57 ; 43 min, 159 °C, 8.57, 0.62) were found to produce the highest MRP yields. The products were subsequently used to evaluate the efficacy to retard lipid oxidation in a model cookie dough system. While Glu-Lys MRPs exhibited antioxidant activity in the cookie dough model, Fru-Lys MRPs showed prooxidant activity regardless of the presence of Cu²⁺. Fractionation of MRPs derived from specific Glu-Lys (Expt. Nos 3 and 13) and Fru-Lys (Expt. Nos 5 and 11) reaction conditions using Cu²⁺ chelating chromatography resulted in two principal metal chelating components having molecular weights of 5.7 kD and 12.4 kD, respectively. Glu-Lys MRPs (5 kD) decreased (p&gt;0.05) Fe²⁺ induced nicking of PM2 bacteriophage DNA, relative to the nicking caused by both metals alone or metals associated with Fru-Lys MRPs (5 kD). Both MRP sources induced a higher percentage of DNA nicking in the presence of Fe²⁺ relative to the nicking caused by MRPs alone. The extent of DNA breakage by polyvalent metals and MRP reactants was pH dependent and corresponded to the reducing potential of MRPs in modulating the Fenton reaction. Cytotoxicity evaluations using C3H10T1/2 mouse embryo fibroblast cells demonstrated that MRPs could decrease cytotoxicity, regardless of Cu²⁺ concentration or preincubation conditions used. Individually, MRPs and Fe³⁺ enhanced cytotoxicity during direct application; a similar effect was not noted with Fe²⁺. These findings indicated that metal chelating and reducing activities are important factors in determining model MRPs efficacies in modulating metal catalyzed cytotoxicity. Coffee derived MRPs (5-6 kD) possessed a relatively higher percentage of carbon but exhibited low reducing and higher Cu²⁺ chelating activity compared to model MRPs. As a result, coffee MRPs effectively reduced metal catalyzed in vitro cytotoxicity. The complexity of different MRPs due largely to variations in reaction conditions was shown to influence both antioxidant and prooxidant characteristics of specific MRPs. These results are important in determining the functional and safety properties of MRPs.