THE RED PIGMENT PREPARED FROM AUCUBIN AND AMINO-ACID

Aucubin (AC) is an iridoid glucoside contained in Aucuba japonica Thun b, and Plantago asiatica L. AC was hydrolyzed by beta-glucosidase to a ucubigenin (ACN), a reactive aglycone, and it reacted with a certain a mino acid to form a red pigment. The conditions of this coloring react ion were similar to those of the red pigment formed from geniposidic a cid (GSA) and amino acid. it was suggested that ACN became a dialdehyd e form in the aqueous solutions and then reacted with amino group of a mino acid lo form the intermediate by amino-carbonyl reaction. Further , the coloring reaction was promoted with healing and acidity by organ ic acid, and the reaction mixture deepened with the passage of lime an d finally gelled. The molecular mass of the pigment prepared from AC a nd glutamic acid showed higher than that of the pigment produced from GSA under the same reaction condition. The color of the pigment produc ed from AC and glutamic acid showed high stability in a pH range of 4- 7, however, it precipitated at pH 3. The color deepened and decreased the red tone with heal treatment. Light exposure caused hypsochromic s hift and fading of the color. The red pig ment produced from a mixture of AC and GSA showed red color tone depending upon the proportions of these iridoid glucosides and was not separated into each pigment orig inated from AC or GSA by a gel chromatography. These results suggested that the forming mechanism of the red pigment produced from AC was a similar to that of GSA.