Xanthophyll

Xanthophylls are yellow pigments found all around nature. They belong to a group of compounds called carotenoids, which also includes carotenes. The name xanthophyll comes from Greek words meaning "yellow" and "leaf," because these pigments create a yellow band when scientists study leaf colors.

These pigments are important in plants, giving many leaves and flowers their bright yellow colors. They also help protect plants from too much sunlight. Xanthophylls can be found in many foods we eat, like corn, peas, and eggs, which is why these foods have yellow hues.

Xanthophylls are interesting to scientists because they were one of the first plant pigments studied using a method called chromatography. This helped researchers learn more about how plants make and use colors.

Molecular structure

Xanthophylls and carotenes are both types of carotenoids, which means they have similar structures. However, xanthophylls contain oxygen atoms, while carotenes are made only of hydrocarbons and do not have oxygen. This difference makes xanthophylls more polar than carotenes, which helps them separate from carotenes during certain tests. Xanthophylls can have their oxygen in the form of hydroxyl groups or as oxygen atoms connecting to form epoxides.

Occurrence

Xanthophylls, like other colorful plant parts, are found most in the leaves of green plants. They help manage light energy and protect a special part of chlorophyll when there is too much light.

Animals, including humans, get xanthophylls from the plants they eat. For example, the yellow color in chicken egg yolks comes from xanthophylls in their food, mainly lutein.

In our eyes, the yellow spot called the macula lutea gets its color from lutein and zeaxanthin, which we get from eating certain foods. These help protect our eyes by blocking blue and ultraviolet light. They do not help us see directly, but they play a role in how we sense certain kinds of light.

Example compounds

Xanthophylls include several important compounds such as lutein, zeaxanthin, neoxanthin, violaxanthin, flavoxanthin, and α- and β-cryptoxanthin. Among these, β-cryptoxanthin is special because it has a beta-ionone ring and can act like a vitamin for some animals that eat plants. However, this only works for animals that have a certain enzyme. In some insects, certain xanthophylls might help with vision, unlike other types of carotenoids like beta carotene.

Xanthophyll cycle

The xanthophyll cycle is a process in plants that helps protect them from too much sunlight. It involves changing certain yellow pigments, called xanthophylls, from one form to another.

When there is too much light, plants change a pigment called violaxanthin into another pigment called zeaxanthin. This change helps the plant safekeep its energy and protect its leaves. Different types of tiny water organisms, like diatoms and dinoflagellates, also have their own versions of this cycle to protect themselves from bright light.

Food sources

Xanthophylls are found in young leaves and in special leaves called etiolated leaves. They are also in many foods such as papaya, peaches, prunes, and squash. Some vegetables like kale have a lot of these pigments, with about 18 mg in every 100g. Spinach has about 11 mg, parsley has about 6 mg, peas have about 3 mg, squash has about 2 mg, and pistachios have about 1 mg in every 100g.