Basella alba is an annual plant, which grows leaves that look like spinach. The leaves of Basella alba are edible, but effective methods of using fruits have not been reported yet. The fruits of Basella alba are vivid purple, and there is a possibility of being effective for products such as foods and cosmetics. To improve the appearance of products or to make use of the color sense derived from raw materials, pigments are also added and retained in the products. Various kinds of surfactants are added in food, cosmetics and daily toiletries for emulsifying oil and water. Many kinds of additives are also mixed in all products. All products are exposed to light in the sales process for the prolonged storage time at shops and homes. Furthermore, product users are also exposed to sunlight, and raw materials of the products would receive stimulus of the sunbeam. Such an environmental stimulus should be assessed in the product with pigment–surfactant mixed system. In this study, we investigated two types of discoloration in heating the natural pigment–surfactant mixed system by irradiation of artificial sunlight. In the experiments with artificial sunlight irradiation, under the condition that the surfactant concentration was higher than critical micelle concentration, the decolorization rate of Basella alba extract increased. Also, their decolorization rate was affected by dissolved oxygen.
