On the effect of tetraborate ions in the generation of colored products in thermally processed glycine-carbohydrate solutions

The effect of tetraborate ions on Maillard browning was investigated in a series of monosaccharide-glycine reactions in aqueous bis-tris buffer at pH 7.2. Addition of borax (sodium tetraborate) in catalytic amounts led to enhanced browning measured by absorbance at 420 nm in the order xylose > arabinose > galactose approximately = fructose > ribose > mannose > rhamnose, and the degree of browning with borax was uniformly greater than that produced by phosphate on an equimolar basis. A mechanism is proposed for borax catalysis in which monosaccharide-borate complexation shifts carbohydrate equilibria to favor open-chain (carbonyl) forms, thereby enhancing the rate of the Maillard reaction.