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The Maillard reaction is often studied in buffered model systems. Phosphate, in particular, catalyzes the browning reaction between amino acids and sugars. The addition of citric acid to model systems containing ascorbic acid and glycine increased both the color formation and the degradation of ascorbic acid in relation to increasing concentration.

The objective of this work was to determine the kinetics of the reaction between glucose and glycine and to determine how it was influenced by citrate, glucose, and glycine concentration.

Model systems containing glucose (0 - 0.4 M), glycine (0 - 0.4 M) and sodium citrate (0-0.5 M; initial pH 5.5) were incubated in a water bath at 50 C. Browning of model systems was observed at 420 nm. The kinetics of the reaction were determined with non-linear regression analysis, using the equation, A₄₂₀=at² + bt. The effect of citrate, acetate, glucose, and glycine concentration on parameters a and b was examined. ECHIP software was used for experimental design and analysis.

The non-linear regression relationship fitted all absorbance-time data for citrate. The absolute values of parameters a and b increased with increasing citrate, glucose, and glycine concentrations. Changing the glucose or citrate concentration had a greater effect on these parameters than changing the glycine concentration. Parameter a increased ten, and parameter b four times, when glucose concentration increased from 0.1 to 0.25 M while glycine (0.1 M) was constant. Whereas parameter a increased by approximately three and parameter b remained constant when glycine increased while glucose was kept constant. When both glucose and glycine concentration were increased the change in a and b was exponential.

Since the kinetics of the glucose and glycine reaction are influenced by buffer concentration, the presence and concentration of organic salts, such as citrate, must be taken into consideration when modeling the Maillard reaction.