Carotenoids may be unmasked by a loss of chlorophyll but also may change in fruit during ripening. The most familiar change is the formation of the red pigment lycopene in ripening tomatoes. Similar changes occur in other fruit but have been less well studied. Caroten-oids are synthesized starting with acetyl-CoA condensation to form mevalonic acid that is converted to isopentenyl pyrophosphate. Iso-pentenyl pyrophosphate condenses to form a C20 compound that further condenses to C40 and cyclization results in a carotenoid. Many specific types of carotenoids are formed by isomeric modification, desaturation, cyclization, and introduction of oxygen molecules.

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