仙人掌果汁色素為水溶性色素。此色素在pH值2∼8間皆為紫紅色，適用的食品著 色酸鹼範圍廣，遠較花青素可應用範圍為廣。Betanin 與 isobetanin 係仙人掌果汁中兩主 要色素，兩者可見光之吸收光譜類似，皆呈紫紅色。 仙人掌果汁色素對酸鹼安定性：pH5、 pH4 ＞ pH6、pH3 ＞ pH7、pH2，故在強酸及中性下，較不安定。 仙人掌果汁色素，在 pH3 、 pH5 及 pH7 下，不同溫度的熱安定度：25 ℃＞ 60 ℃＞ 80 ℃＞ 95 ℃。 此色素對熱 敏感，在最適 pH 值時，80 ℃及 95 ℃加熱之半衰期分別為 30 分鐘、10 分鐘。故對於熱 加工食品，須在很短時間內完成加熱殺菌，以保持固定的色澤。空氣對此色素的影響不大， 光線對此色素安定度影響較大。 故存放此樣品時，以不透光容器較佳。對β -glucosidase 水解作用，在水解 20 min 時，isobetanin 水解 90 ％，而 betanin 水解 25 ％，較安定 。

　　　　　Opuntia dillenii fruit juice pigments are water-soluble. It is purple red between pH2 ∼ 8. Betanin and isobetanin are two major pigment in Opuntia dillenii fruit juice. Both betanin and isobetanin are similar in visible absorption spectrum and color of purple red. The stability of pigment at different pH value are in following order: pH5、pH4 > pH6、 pH3 > pH7、 pH2. Its thermal stability order is 25 ℃ > 60 ℃ > 80 ℃ > 95 ℃ at optimal pH. Half life of the pigment at 80 ℃ and 95 ℃ is 30 min and 10 min respectively. Therefore heat processing of the juice should be done in the short time to minimize the thermal degration of pigment. Air showed little effect on stability. Whereas light exhibited some detrimental to stability. Betanin showed more resistant to β -glucosidase hydrolysis than isobetanin. The degree of betanin and isobetanin hydrolysis by β -glucosidase in 20 min at room temperature is about 25% and 90% respectively.