摘要：Photostability of Food Red No. 40, a synthetic food coloring not approved in Japan, was compared to those of other synthetic and natural Food Reds commonly used in Japan. In a short-term (10 days) experiment, an ultraviolet light was irradiated onto solutions of 6 synthetic Food Reds containing ascorbic acid at a pH of either 3.0 or 6.5. Food Reds No. 3 and No. 104 rapidly faded even in the absence of the ascorbic acid. Fading of Food Reds No. 2 and No. 102 was accelerated by the ascorbic acid, the effect of which was more significant at pH 3.0 Food Reds No. 40 and No. 106 were fairly stable and over 50% of the color remained after 10 days in the presence of the ascorbic acid. In a long-term (24 weeks) experiment, solutions of 6 synthetic and 7 natural Food Reds were placed under mid-summer sunlight, ultraviolet light, indoors or in the dark. All natural Food Reds became unstable, and lost their color even in the dark. On the contrary, all synthetic Food Reds including No. 3 and No. 104 were stable in the dark and remained unchanged after 24 weeks. Under sunlight, Food Reds No. 3 and No. 104 lost their color completely within 1 week, No. 102 gradually fading at its lower concentration. Food Reds No. 2, No. 40 and No. 106 were quite stable with no fading occurring. A long-term experiment with 4% acetic acid-, 20% ethanol-, and 4% sodium carbonate-solutions of Food Reds, also proved the stability of No. 40 and No. 106.
