Carotenoid pigments are found in all kinds of plants, and they absorb energy and protect against damage from light as photosynthesis takes place. Either red or yellow in color, carotenoids are visible when chlorophyll, the substance that converts light to energy in plants and certain bacteria, is depleted. The colors that tree leaves change to in fall are due to the exposure of carotenoid pigments. These pigments also have antioxidants, and the consumption of carotenoids can protect against heart disease and cancer in humans and other species.
Molecularly, most of the carotenoids involved in these processes feature a hydrocarbon backbone. Between three and 15 double bonds exist along the length of this backbone, and the bond count has a direct relationship to the part of the spectrum a carotenoid can process. Light between 400 and 500 nanometers (nm) is typically absorbed by these molecules. Phytoene is the first type produced from the assembly of various molecular components, and is critical in the formation of other carotenoids. The basic pigments can be biosynthesized into other compounds, such as beta carotene and lycopene.
Carotenoids play a significant protective role because they block the effects of oxygen particles and radicals when light and photosensitizers such as chlorophyll interact. Radiant energy is transferred by carotenoid pigments to individual chlorophyll molecules, while excess energy is dissipated as part of the xanthophyll cycle in some plants and algae. Chlorophyll molecules that remain in an active state can be regulated as well. On a molecular level, carotenoids help to bond the molecules of photosynthetic pigment-proteins.
Consumption of plant-based organisms leads to the metabolic processing of the carotenoid pigments in salmon, shrimp, lobsters, and creatures. The coloring of such fish and crustaceans comes from the pigments found in the food they eat. For example, wild salmon that eat shrimp are much redder in color than salmon produced in farms. It is difficult to harvest carotenoids naturally, but genetic engineering is making the prospect more optimistic. Chemically synthesized pigments do not yield the same result as natural ones.
Various kinds of carotenoids exist in plants, bacteria, fungi, and algae. Phytoene is one form of pigment that can be metabolized into beta carotene which, along with other compounds, is used to produce vitamin A as well as retinal fluid in mammals. The photosynthetic properties and impact on human health makes carotenoid pigments one of the most important biological elements in nature.