**2. Bioaccessibility of Carotenoids**

Although xanthophylls have the potential to prevent various degenerative diseases as described above, the bioavailability of carotenoids is lower than that of other fatty components such as 

΅-tocopherol and triacylglycerols [21–24]. The major cause of the low bioavailability is the poor solubility of carotenoids in digestive fluid. Carotenoids must be solubilized in the digestive fluid via several steps before uptake by intestinal epithelial cells can occur [25]. First, carotenoids are released from the food matrix. In some types of food, the matrix interferes with the release of carotenoids. Carotenoids are hardly released from raw vegetables due to the solid structure of the cell walls, but processing and heat treatment of foods accelerate the release of carotenoids by destroying the structures [26]. The released carotenoids must be well dispersed in the gastrointestinal tract. However, the carotenoid dispersion is greatly limited in digestive fluid due to the high hydrophobicity of C40 isoprenoid carbon skeletons. In this step, dietary lipids facilitate the carotenoid dispersion. Carotenoids are dissolved into the dietary lipids and then dispersed as an emulsion in the digestive fluid. The digestion of the dietary lipids in the emulsion progresses with the aid of lipolytic enzymes and bile fluid, and finally the carotenoids are solubilized in the mixed micelle. The mixed micelle consisting of bile acids, phospholipids, cholesterol, fatty acids, and monoacylglycerols has a disk-like shape, in which the outside is surrounded by the bile acids [27]. Carotenoids solubilized in the mixed micelle are thought to become accessible to uptake by the intestinal epithelial cells. Thereby, the bioaccessibility is defined as the ratio of carotenoids solubilized in the mixed micelles to the total carotenoids ingested. The bioaccessibility, dependent on the food matrix, processing, cooking, and structures of carotenoids, is an important factor for bioavailability. 
