Browning Reaction of 2,3-Diketo-L-gulonic Acid in a Weakly Alkaline Solution

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Browning reaction and the degraded compounds of 2,3-diketo-L-gulonic acid (DKG) in a weakly alkaline solution were studied. To obtain reproducible results, the experimental conditions were fixed as 20 mM DKG in phosphate buffer (i=1.0, pH 8.0). DKG was quite reactive and readily turned to brown colored substances: its degradation occurred almost completely by heating for 30 min at 50℃. However, the brown color formation reached its maximum around the reaction time of 3 hrs, followed by gradual decolorization. From the size-exclusion chromatography of the reaction mixture, three main products (P-1, P-2, and P-3) were obtained. The molecular weights of the products corresponding to P-1, P-2, and P-3 were presumed to be 800, 450, and 200, respectively, from the results of gel chromatography. The brown colored products, P-2 and P-3, reached to their maxima after incubation at 50℃ for 3 hrs, pH 8.0, while that of P-1, arrived to the maximum after 5 hrs incubation. The net changes (450 to 500nm) in the log absorbance (ΔA) regarding to the brown products, were 0.428 for P-1, 0.860 for P-2, and 0.602 for P-3, suggesting that P-1 shows the darkest tone, followed by the decreasing order of P-3 and P-2. The brown products were approximately in the yields of 3.2, 12.9 and 9.7% for P-1, P-2, and P-3, respectively. The brown products, P-1, P-2 and P-3, seemed interchangeable. From the results of mass spectrometric analysis, the P-2 and P-3 were presumed to have the same backbone structure. Possible structures of the brown products, P-2 and P-3 and the degradation pathways were proposed.
大阪府立大学の論文
1997-03-31

Browning Reaction of 2,3-Diketo-L-gulonic Acid in a Weakly Alkaline Solution

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