The Greening of Steamed Glutinous Rice Colored Yellow with Gardenia Fruit(Gardenia jasnoides Ellis)

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  • クチナシ果実で黄色に染めたおこわの緑変について

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When glutinous rice (R) colored with the aqueous yellow extract (YE) of the Gardenia fruit (GF) was steamed, the color sometimes changed from yellow to green unexpectedly. The experiment was done to clarify the phenomenon of the greening. The greening occurred when R was steeped in YE at 30～40℃ for 24 hours and then steamed, and no greening occurred at 20℃ or below for 24 hours or at 30℃ for 12 hours. The greening was weaker when the well-washed R was steamed, and stronger when R with addition of rice bran (RB) was steamed. Furthermore, an experiment of greening YE was carried out by using RB or its extract. The result showed that the greening did not occur when RB was heated previously. The greening was inhibited when silver ion was added. The green liquid obtained by this experiment had a maximal absorbance at 440 nm and 590 nm in the visible range. We may conclude on the basis of this experiment that a green color consits of two kinds of color, namely, yellow and blue. The phenomenon of greening seems to indicate that iridoid glycoside (such as geniposide) contained in GF was liberated into iridoid compound (such as genipin) by the function of enzyme contained in R or RB. The phenomenon also revealed that iridoid compound turns into blue color when it was heated with amino acids.

Journal

  • 調理科学

    調理科学 22 (3), 208-212, 1989-09-20

    調理科学研究会

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