Stability of a Pigment formed by the Reaction of 5, 6-Diacetyldehydro-L-ascorbic Acid with Glycine

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Dehydro-L-ascorbic acid (DHA) or 5, 6-diacetyldehydro-L-ascorbic acid (AcDHA) prepared from 5, 6-diacetyl-L-ascorbic acid was heated with glycine in 90% ethanol at 80°C for 30 minutes. The resultingred pigments were separated from a cellulose powder column by eluting with methanol and then precipitated from the methanolic solution, after concentration, with the addition of ether.<BR>DHA-glycine and AcDHA-glycine pigments have three absorption maxima at247, 382 and 520, and 246, 387 and 522 mμ in ethanol, and at 247, 383 and 510, and 245, 385and 510 mμ in water, respectively.<BR>The stability of both pigments in buffer solutions of various pH and in aqueous ethanol was investigated. Both pigments were unstable at pH 2, 10 and 12, and were most stable at pH 6. AcDHA-glycine pigment was more stable than DHA-glycine pigment at pH 4, but was less stable than DHA-glycine pigment at pH 8.<BR>AcDHA-glycine pigment was more stable than DHA-glycine pigment in aqueous ethanol. There were little differences in the stability of AcDHA-glycine pigment according to ethanol concentration, whereas the stability of DHA-glycine pigment increased with the increase of ethanol concentration.
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