Introduction
Rice is a grain cultivated in many countries worldwide, particularly in East and Southeast Asia. Rice bran, a non-edible part of rice, accounts for approximately 10% of its weight and is known to contain various functional ingredients (Ghosh, 2007). Phytosterols and their esters are among the functional components of rice bran. Phytosterols are used as food additives, such as natural emulsifiers and processing aids, and are widely found in pharmaceuticals and cosmetics. Their biological functions have been studied in medicine and food, and one of their effects is the suppression of blood cholesterol (Pollak, 1953, Joneset al. , 2000, Vissers et al ., 2000). Phytosterols are also known to exert anti-inflammatory effects in cosmetics (Loizouet al. , 2009). However, the biological functions of the ester forms of phytosterols have not been elucidated.
Phytosterols differ depending on the plant species. Rice bran contains large amounts of the plant sterols β-sitosterol and campesterol, as well as the triterpene alcohols cycloartenol and 24-methylenecycloartenol (Akihisa et al. , 1996, Shimotoyodome et al ., 2017). We developed a method for producing RSE from by-products of the rice bran oil refining process. RSE is an oil rich in esters of phytosterols, triterpene alcohols, and fatty acids that has been confirmed to have high water-retention and emollient effects(Janeš et al. , 2018). However, there are few examples of biological verification of the cosmetic effects of phytosterols using cultured skin cells. Therefore, in this study, we examined whether phytosterol esters derived from rice bran have effects on the skin.