A group of dyes belonging to the tetra-terpenes with over 800 different species occurring in nature. They are widespread in the animal and plant kingdom and cause a yellow, green, orange to reddish coloration. During photosynthesis, carotenoids are responsible for protection against photo-oxidation and for energy transfer. The most common carotenoids are β-carotene (carrot), a precursor of vitamin A and lutein. Lutein-5,6-epoxide, luteoxanthin, neoxanthin, violaxanthin, xanthophylls and zeaxanthin occur in lower concentrations. Carotenoids are also used for colouring and as flavour enhancers in foods. Some carotenoids act as antioxidants and therefore have a preventive effect on many diseases such as Alzheimer's, arteriosclerosis, cataracts, skin ageing, cancer, Parkinson's disease and rheumatism.