Carotenoid

Carotenoids are yellow, orange, and red colors that come from plants, algae, some bacteria, and fungi. They give color to many foods and animals we see every day, like pumpkins, carrots, corn, tomatoes, canaries, flamingos, salmon, lobster, shrimp, and daffodils. Scientists have found over 1,100 different kinds of carotenoids. These can be grouped into two types: xanthophylls, which contain oxygen, and carotenes, which have no oxygen.

All carotenoids are made from eight isoprene units and have 40 carbon atoms. They absorb light in the violet to green range, which is why they look yellow, orange, or red. In plants and algae, carotenoids help with two important jobs: they catch light energy for photosynthesis and protect the plant from too much sunlight. Some carotenoids, like β-carotene, α-carotene, β-cryptoxanthin, and γ-carotene, can be turned into vitamin A in our bodies. In our eyes, pigments like lutein, meso-zeaxanthin, and zeaxanthin help with vision. Scientists are still studying how they work.

Structure and function

Main articles: carotenes and xanthophylls

Carotenoids are special colors made by plants, algae, and some tiny living things. They give foods like carrots, tomatoes, and corn their bright colors. They also help plants use sunlight to grow.

Carotenoids have two main types: carotenes, which are made of carbon and hydrogen, and xanthophylls, which also have oxygen. They help protect plant cells and give plants colors from yellow to red.

Regulation

Plants make carotenoids because of many different things. Light can turn on genes that help plants make more carotenoids. Plant hormones, like auxins and abscisic acid, also affect how much carotenoid a plant makes, especially when it faces hard times.

Things like drought or pests can make plants produce extra carotenoids. This helps the plant stay safe and healthy in difficult situations.

Morphology

Carotenoids are found outside the cell nucleus in places like tiny drops of fat and small groups inside cells. Scientists use special tools to see and measure these colorful pigments, especially in very small plants called algae. Researchers have made special proteins to find a type of carotenoid called lycopene in both animal and human cells.

Foods

Beta-carotene, found in pumpkins, sweet potato, carrots, and winter squash, gives these foods their orange-yellow colors. Dried carrots have the most beta-carotene of any food. The Vietnamese gac fruit has lots of lycopene, a type of carotenoid that gives tomatoes their red color. Even green foods like kale, spinach, collard greens, and turnip greens contain beta-carotene.

Carotenoids are important for our health. They help us see better and keep our skin healthy. Animals, including flamingos, get their colorful feathers from carotenoids in their food. Humans need to get carotenoids from the foods we eat because our bodies cannot make them. Eating these foods with some fat, like oil, helps our bodies absorb the carotenoids better.

Plant colors

Carotenoids are pigments that give yellow, orange, and red colors to many plants. You can find them in fruits like tomatoes and vegetables like carrots. They also color the leaves of trees in the fall, such as hickories, ash, maple, and birch. While carotenoids make yellow and orange colors, red and purple hues in autumn leaves usually come from a different kind of pigment called anthocyanins. These pigments appear when the green chlorophyll fades away.

Bird colors and sexual selection

Dietary carotenoids and their metabolic derivatives make birds bright yellow or red. Many bird species have carotenoid coloration, and this ability has evolved many times in birds. Carotenoid coloration shows high levels of sexual dimorphism, with adult male birds generally displaying more vibrant colors than females of the same species.

These differences happen because of the selection of yellow and red coloration in males by female preference. In many bird species, females spend more time and resources raising offspring than males, so they choose high-quality mates. Bright carotenoid coloration is often a sign of male quality. However, in some cases, such as with stickleback fish, more colorful males might not be the best choice, as they may not protect their sperm as well from damage.

Aroma chemicals

When carotenoids break down, they make special chemicals like ionones, damascones, and damascenones. These chemicals help create nice smells in perfumes. Even in small amounts, β-damascenone and β-ionone give flowers, like the rose, their sweet fragrance. You can also find these pleasant smells in black tea, aged tobacco, grape, and many fruits.

Disease

Some bacteria make carotenoids to protect themselves. For example, a carotenoid called staphyloxanthin gives some kinds of Staphylococcus aureus their golden color. This pigment helps the bacteria stay safe from substances our bodies use to fight infections.

Biosynthesis

Carotenoids are made from small molecules called isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Plants use two ways to make these building blocks. One way, found outside the chloroplasts, is used to make cholesterol in animals. The other way, used in chloroplasts, helps create carotenoids.

The process starts with two molecules of geranylgeranyl diphosphate (GGPP) joining together. This makes a colorless molecule called phytoene, which then changes into lycopene, a red molecule. Lycopene can change into different carotenoids like α-carotene and β-carotene. These can be further changed into xanthophylls, which add yellow and orange colors to plants.

Naturally occurring carotenoids

Carotenoids are colorful pigments found in many plants and other living things. They give bright yellow, orange, and red colors to foods like pumpkins, carrots, tomatoes, and corn. They also color animals such as flamingos and salmon.

More than 1,100 different carotenoids have been identified. They can be grouped into two main types: xanthophylls, which contain oxygen, and carotenes, which are made only of carbon and hydrogen without oxygen. These pigments help protect living things from harmful sunlight and support some organisms in making food.