A class of hydrocarbons (carotenes) and their oxygenated derivatives which exhibit chemopreventive properties. Carotenoids are pigments found in green, yellow, and leafy vegetables, and yellow fruits. The pigments are fat-soluble, unsaturated aliphatic hydrocarbons functioning as provitamins and are converted to vitamin A through enzymatic processes in the intestinal wall. CRCH Definition: Class of compounds usually consisting of a hydrocarbon chain of 40 carbons, nine conjugated double bonds, and one or two cyclic structures at the ends of the conjugated chain. NCI-GLOSS Definition: A yellow, red, or orange substance found mostly in plants, including carrots, sweet potatoes, dark green leafy vegetables, and many fruits, grains, and oils. Some carotenoids are changed into vitamin A in the body and some are being studied in the prevention of cancer. A carotenoid is a type of antioxidant and a type of provitamin."