Chemistry of nonenzymic browning. X. Difructose-amino acids as intermediates in browning reactions

The visible and ultraviolet spectra of various mixtures stored at 37.5 or 50 °C were compared. Each mixture consisted of an aqueous syrup of sorbitol buffered at pH 5.5, to which an amino acid (0.1M) and one of the following : difructose-glycine, fructose-glycine, or glucose (0.05M) were added. Difructose-glycine mixtures browned much faster than those containing fructose-glycine, and there was very little browning in the glucose mixtures. The rapid browning with difructose-glycine is attributed to the non-nitrogenous carbonyl decomposition products. Bisulphite largely eliminated the production of material absorbing light above 240 mµ, except for a chromophore with a maximum at 295 mµ, derived from fructose-glycine. All the amino acids gave similar browning curves, but the rates varied. The greatest differences occurred in mixtures containing difructose-glycine, ?-aminobutyric acid giving the highest rates. The results show that diketose-amino acids can be important intermediates in non-enzymic browning reactions.