Abstract
Steamed glutinous rice is colored yellow by treating with aqueous extract of the Gardenia fruit(GF)to give what we call “Ouhan” (yellow cooked rice), but sometimes green or deep olive color develops by steaming of rice unexpectedly. This greening is thought due to the blue discoloration of colorless geniposide that is contained in the GF extract. To elucidate the mechanism of the greening, geniposide was prepareted from GF, and the blue discoloration wasinvestigated by using an aqueous model system(geniposide-gulcosidase(β)-glycine-water)and rice. Blue discoloration occured in this model system on prolonged incubation at optimum pH of 5.0-6.0 and temperature of 35-40°C. The discololoration loration was increased by increasing the amounts of geniposide and enzyme, and by the addition of glycine. The blue color formed from geniposide was found tocontain a purple color. When rice was steeped in a geniposide solution at 30°Cfor 24 hrs and then steamed, it showed agrayish deep blue color. From these results, it may be concluded that the greening phenomenon observed in making “Ouhan” is clue to two pigments, yellow and blue (includingpurple).
