紅茶の水色変化におけるpHおよび有機酸の影響
1992 年 25 巻 3 号 p. 222-227
詳細
1992 年 25 巻 3 号 p. 222-227
Effects of pH and organic acids on the color of infusion of black tea have been studied by color measurement and pigment separation.
The color of infusion of black tea became brighter orange with lower value of pH and more reddish brown with higher value of pH.
Infusion with buffers of pH 2.2-8.0 showed that optical density of butanol and water layers increased with higher pH in comparison with Methyl-iso-butylketone layer.
Methyl-iso-butylketone layer which mainly contains theaflavins, had higher optical density with lower value of pH and lower optical density with higher value of pH. Butanol layer which mainly contains thearubigins, and water layer which contains water soluble pigment, had higher optical density with increase of pH.
When the 2-4×10-5 mol of acetic acid, lactic acid, gallic acid, oxalic acid, malic acid, succinic acid, tartaric acid or citric acid was added to the infusion of black tea, the different effect on the color was not recognized.
Ascorbic acid had the effect of increasing yellow and rising the value and chroma of the infusion of black tea in comparison with other organic acids.
It is considered that the change of color of infusion of black tea, by adding lemon, is due to ascorbic acid and the decrease of pH.
