Xanthophylls are a class of carotenoid pigments produced by plants and some other photosynthetic organisms like algae. Carotenoids are organic compounds made up of isoprene units and are responsible for many of the red, orange, and yellow colors seen in plants. Xanthophylls are distinguished from other carotenoids by the presence of oxygen-containing functional groups on their structure. They absorb light in the blue-green to yellow region of the visible spectrum and play various roles in photosynthesis and photoprotection in plants and algae. Some key functions of xanthophyll pigments include:
Roles in Photosynthesis
– Light harvesting – Xanthophylls can absorb light energy and transfer it to chlorophylls during photosynthesis. This allows plants to utilize a broader range of visible light. Lutein and violaxanthin are two xanthophylls involved in light harvesting.
– Photoprotection – Excess light can damage the photosynthetic machinery. Xanthophylls like zeaxanthin can help dissipate this excess excitation energy and prevent damage in a process called non-photochemical quenching.
– Thylakoid membrane stabilization – Xanthophylls are incorporated into the thylakoid membranes of chloroplasts and help maintain membrane structure and organization. This is critical for photosynthetic processes that take place in the membrane.
Antioxidant Properties
Many xanthophylls act as antioxidants, helping to neutralize reactive oxygen species that can damage cells. Key antioxidant xanthophylls include:
– Lutein – The most abundant xanthophyll found in green leafy tissues. It absorbs blue light and helps prevent oxidative damage to tissues.
– Zeaxanthin – Accumulates in areas needing high photoprotection like leaves exposed to full sun. It is a powerful antioxidant that may help prevent eye diseases.
– Astaxanthin – Found in algae and bacteria. It is a strong antioxidant and anti-inflammatory compound with numerous health benefits.
Coloration
Xanthophylls are responsible for the yellow colors seen in many plant parts and products:
– Lutein colors marigold flowers and corn.
– Zeaxanthin colors many yellow fruits like mangos and oranges.
– Astaxanthin gives salmon, lobster, and shrimp their distinctive reddish-pink coloration.
Health Benefits
When consumed by animals, xanthophylls can have beneficial health effects:
– Lutein and zeaxanthin accumulate in the eye and help prevent age-related macular degeneration and cataracts.
– Astaxanthin may boost immune function, reduce risk of heart disease, and have anti-cancer properties.
– Beta-cryptoxanthin found in fruits like oranges may lower risk of inflammatory joint diseases like arthritis.
Structures of Key Xanthophylls
| Xanthophyll | Structure |
|---|---|
| Lutein |  |
| Zeaxanthin |  |
| Violaxanthin |  |
| Astaxanthin |  |
Biosynthesis of Xanthophylls
Xanthophylls are derived from carotenes like lycopene and beta-carotene. Enzymes introduce oxygen-containing functional groups to make various xanthophyll compounds:
– Beta-carotene can be converted to zeaxanthin by the addition of hydroxyl groups.
– Zeaxanthin epoxidase adds epoxy groups to zeaxanthin to produce violaxanthin.
– The de-epoxidase enzyme converts violaxanthin to antheraxanthin and then zeaxanthin in high light.
– Hydroxylation and ketolation of zeaxanthin produces astaxanthin. This occurs in algae and some bacteria.
Dietary Sources of Xanthophylls
Good dietary sources of the main xanthophylls include:
Lutein:
– Kale, spinach, collard greens, turnip greens
– Corn, green beans, broccoli
– Egg yolks
Zeaxanthin:
– Corn, orange peppers, orange fruit
– Greens like kale, spinach, collards
– Salmon
Astaxanthin:
– Salmon
– Trout
– Shrimp, lobster
– Microalgae
Absorption and Transport in the Body
When consumed in the diet, xanthophylls follow similar absorption and transport pathways as other carotenoids:
– Released from food matrix during digestion
– Incorporated into mixed micelles containing fat and bile acids
– Absorbed by intestinal epithelial cells
– Incorporated into chylomicrons for transport in blood
– Carried by lipoproteins to target tissues like eyes and skin
– Accumulate preferentially in certain tissues based on needs
Factors Affecting Xanthophyll Bioavailability
Several factors influence the bioavailability of xanthophylls from foods:
– Food matrix – Easier to absorb from processed foods vs whole foods
– Cooking – Heat disrupts the food matrix and improves bioavailability
– Dietary fat – Needed for formation of mixed micelles to aid absorption
– Other carotenoids – Competition for absorption into intestinal cells
– Nutrient status – Low iron can reduce conversion of provitamin A carotenoids into xanthophylls
– Genetic factors – Genes influence carotenoid metabolism and absorption
Supplementation
While foods are the best sources of xanthophylls, supplements are also available:
– Lutein and zeaxanthin supplements for eye health
– Astaxanthin supplements derived from algae
– Mixed carotenoid supplements with various xanthophylls
– Often use stronger synthetic versions with higher bioavailability
– Helps increase intake for those lacking sufficient dietary sources
– Further evidence needed to establish long-term safety and efficacy
Conclusion
In conclusion, xanthophyll pigments like lutein, zeaxanthin, and astaxanthin play critical roles in plant and human health. They act as light harvesters and antioxidants in photosynthesis, provide vibrant plant coloration, and confer numerous benefits when consumed in the diet. Xanthophylls are synthesized by plants from carotenes and absorbed via micelles like other carotenoids when eaten. Ensuring adequate intake from colorful fruits, vegetables, and other whole foods is ideal to obtain these health-promoting compounds.