Xanthophyll is a collective term referring to a group of yellow, fat-soluble pigments found naturally in plants, particularly in fruits and vegetables.
It belongs to the broader class of carotenoid pigments, which also includes carotenes and lycopene.
Xanthophyll pigments play essential roles in the photosynthetic process and provide protection against oxidative stress in plants.
A. Chemical Structure and Properties
Xanthophylls are derivatives of tetraterpenes, consisting of 40 carbon atoms arranged in an alternating double-bond system.
They contain oxygen atoms in the form of hydroxyl (-OH), epoxy, or keto groups, which distinguish them from carotenes.
Common xanthophyll pigments include lutein, zeaxanthin, violaxanthin, and neoxanthin.
Xanthophylls are generally yellow, orange, or red in color, with varying shades depending on their specific chemical structure.
They are lipophilic (fat-soluble) compounds and are insoluble in water but soluble in organic solvents like hexane, chloroform, and ethanol.
a. Chemical Structure
Xanthophylls are a class of carotenoid pigments that possess an oxygenated structure, containing oxygen atoms in the form of hydroxyl (-OH), epoxy, or keto groups. The basic structural backbone of xanthophylls is a tetraterpene, consisting of eight isoprenoid units linked together, forming a long conjugated chain of 40 carbon atoms. The specific chemical structure of individual xanthophylls varies depending on the number, position, and type of oxygenated functional groups present, as well as the presence and arrangement of double bonds.
Some common examples of xanthophyll structures include:
Lutein: 3R,3’R,6’R-β,ε-carotene-3,3′-diol
Zeaxanthin: 3R,3’R-β,β-carotene-3,3′-diol
Violaxanthin: 5,6,5′,6′-diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-3,3′-diol
Neoxanthin: 5′,6′-epoxy-6,7-didehydro-5,6,5′,6′-tetrahydro-β,β-carotene-3,5,3′-triol
b. Physicochemical Properties
Molecular Weight: Xanthophylls have relatively high molecular weights, typically ranging from 568 to 616 g/mol, depending on their specific structure.
Color: Xanthophylls exhibit a wide range of colors, including yellow, orange, and red, due to their unique conjugated double bond system and the presence of oxygenated functional groups.
Solubility: Xanthophylls are lipophilic (fat-soluble) compounds and are insoluble in water but soluble in various organic solvents, such as hexane, chloroform, ethanol, and acetone.
Light Absorption: Xanthophylls exhibit strong absorption in the visible range of the electromagnetic spectrum, typically between 400-500 nm, which contributes to their bright colors and their role in photosynthesis.
Isomerization: Xanthophylls can exist in different geometric isomeric forms, such as cis and trans isomers, which can influence their physicochemical properties and biological activities.
Thermal Stability: Xanthophylls are generally stable at moderate temperatures, but prolonged exposure to high temperatures or light can lead to their degradation and loss of color.
Oxidation Sensitivity: Like other carotenoids, xanthophylls are susceptible to oxidation, particularly in the presence of light, oxygen, and certain pro-oxidants, which can result in the formation of oxidation products and loss of their biological activities.
B. Sources and Occurrence:
Xanthophylls are widely distributed in nature and are found in various plants, including fruits and vegetables, such as corn, spinach, kale, oranges, and egg yolks.
They are also present in certain algae, bacteria, and fungi.
Some of the richest sources of xanthophylls include marigold flowers, which are often used for commercial extraction of these pigments.
a. Plant Sources
(1) Green Leafy Vegetables
Xanthophylls are abundant in green leafy vegetables like spinach, kale, collard greens, and mustard greens.
The predominant xanthophyll found in these sources is lutein, along with smaller amounts of zeaxanthin and neoxanthin.
(2) Corn and Corn Products
Corn and corn-based products, such as corn oil, corn meal, and popcorn, are rich sources of xanthophylls, particularly lutein and zeaxanthin.
The xanthophyll content can vary depending on the variety, growing conditions, and processing methods.
(3) Fruits and Vegetables
Various fruits and vegetables contain varying levels of xanthophylls, including oranges, peppers, tomatoes, pumpkins, squash, and melons.
The specific xanthophyll profile can differ, with some sources being richer in lutein, while others contain higher levels of zeaxanthin or other xanthophyll pigments.
(4) Egg Yolks
Egg yolks are an excellent source of xanthophylls, primarily lutein and zeaxanthin, which are deposited in the yolks due to the diet of the hens.
The xanthophyll content in egg yolks can vary based on the feed composition and the breed of the hen.
b. Algal and Microbial Sources
(1) Microalgae
Certain species of microalgae, such as Haematococcus pluvialis and Chlorella, are known to produce high levels of xanthophylls, particularly astaxanthin and lutein.
These algal sources are often used for commercial production of xanthophylls for various applications.
(2) Bacteria and Fungi
Some bacteria and fungi have been found to produce xanthophyll pigments, although their commercial exploitation is limited compared to plant and algal sources.
Examples include the bacterial species Bradyrhizobium and the fungus Xanthophyllomyces dendrorhous, which can produce zeaxanthin and astaxanthin, respectively.
c. Commercial Sources
(1) Marigold Flowers
Marigold (Tagetes erecta) flowers are one of the primary commercial sources for the extraction of xanthophylls, particularly lutein and zeaxanthin.
Marigold oleoresin, obtained from the petals, is a rich source of these pigments and is widely used in the food, feed, and supplement industries.
(2) Paprika and Red Pepper
Paprika and red pepper (Capsicum annuum) are also commercially exploited for the extraction of xanthophyll pigments, primarily capsanthin and capsorubin.
These xanthophyll-rich extracts are used as natural food colorants and antioxidants.
C. Biological Functions
In plants, xanthophylls play a crucial role in the photosynthetic process by participating in the light-harvesting complexes and protecting the photosynthetic apparatus from oxidative damage.
They also act as antioxidants, scavenging free radicals and protecting cells from oxidative stress.
In humans and animals, xanthophylls like lutein and zeaxanthin are important for eye health and are believed to protect the macula and retina from damage caused by blue light and oxidative stress.
a. Photosynthesis Function
Xanthophylls play a crucial role in the photosynthetic process in plants, algae and some photosynthetic bacteria. They are components of the light-harvesting complex (LHC) of the vesicle membrane in chloroplasts and act as accessory pigments along with chlorophyll. Chlorophylls absorb light energy in the blue and green regions of the visible spectrum, which is then transferred to chlorophylls to initiate the photosynthetic electron transport chain.
This light-harvesting function of xanthophylls improves the overall efficiency of photosynthesis, especially in low light conditions.
b. Photoprotection
Lutein is photoprotective and protects the photosynthetic apparatus from oxidative damage caused by excess light energy. Under strong light conditions, lutein is involved in the xanthophyll cycle, a process that dissipates excess energy in the form of heat, preventing the formation of reactive oxygen species (ROS) and oxidative stress. The xanthophyll cycle, which includes the interconversion of small xanthophylls, phloem xanthophylls and zeaxanthin, helps to regulate energy flow and protects the photosynthetic machinery from photoinhibition and photodamage.
c. Antioxidant activity
Lutein has strong antioxidant properties as it quenches reactive oxygen species (ROS) and neutralises free radicals. The conjugated double bond system and the presence of oxygen-containing functional groups in the lutein molecules enable them to scavenge and neutralise a variety of reactive oxygen species such as mono-linear oxygen species, superoxide radicals and peroxyl radicals. This antioxidant activity helps protect cells and tissues from oxidative stress-induced damage that has been linked to various diseases and the aging process.
d. Eye health and vision
Two specific lutein pigments, lutein and zeaxanthin, are particularly important for eye health and vision.
These pigments are concentrated in the macula, the central area of the retina responsible for high-resolution vision. Lutein and zeaxanthin act as blue light filters, protecting macular and retinal cells from oxidative damage caused by high-energy blue light and UV radiation. They are thought to play a role in reducing the risk of age-related macular degeneration (AMD), which is the leading cause of vision loss in the elderly.
e. Other potential health benefits
The potential health benefits of lutein have been studied in a variety of areas, including
Cardiovascular health: Some studies suggest that by reducing oxidative stress and inflammation, lutein may have a protective effect against cardiovascular disease.
Cognitive function: Preliminary research suggests that lutein, particularly lutein and zeaxanthin, may have a positive effect on cognitive function and may reduce the risk of age-related cognitive decline.
CANCER PREVENTION: The potential role of lutein’s antioxidant and anti-inflammatory properties in cancer prevention has been explored, but more research is needed in this area.
D. Applications
a. Food colouring agents and additives
Xanthophylls are widely used as natural food colourants to provide a range of yellow, orange and red tones to a variety of foods.
Common applications include
Dairy products (e.g. cheese, butter, yoghurt)
Bakery products (e.g. bread, pastries, biscuits)
Beverages (e.g. fruit juices, soft drinks, alcoholic beverages)
Confectionery (e.g. candy, fudge)
Sauces and condiments
Xanthophylls are often preferred over synthetic food dyes because of their natural origin and health benefits.
Specific xanthophyll pigments used as food colouring agents include lutein, zeaxanthin, capsaicin and xanthophylls from saffron.
b. Animal feed additives
Xanthophylls, especially lutein and zeaxanthin, are added to animal feeds, mainly for poultry and aquaculture.
These pigments enhance the colour of egg yolks, broiler skin and fish meat, making them more attractive to consumers. Xanthophylls in feed also improve the reproductive performance and overall health of animals. Commercial sources of xanthophylls for use in feed additives include marigold extracts, algal sources (e.g. haematococcus) and synthetic forms.
c. Nutritional supplements and health foods
Lutein supplements, particularly those containing lutein and zeaxanthin, are marketed as nutraceuticals for their potential benefits for eye health and vision support. These supplements are often targeted at people at risk for age-related macular degeneration (AMD) or those seeking to maintain healthy vision. Xanthophyll supplements may also be marketed for their antioxidant properties and potential benefits for cardiovascular health and cognitive function.
d. Cosmetics and personal care products
Xanthophylls are used in a variety of cosmetic and personal care products for their colouring and antioxidant properties.
Their applications include
Lipsticks, lip glosses and other lip products (available in yellow, orange or red shades)
Skin care products (e.g., creams, lotions, serums) with antioxidant and photoprotective properties
Hair care products (e.g., shampoos, conditioners) that provide colour enhancement for blonde or white hair
E. Regulatory Status and Safety:
Xanthophylls are generally recognized as safe (GRAS) by the U.S. Food and Drug Administration (FDA) for use as food additives and colorants.
They are approved for use in various food and cosmetic products in many countries, subject to regulatory guidelines and specified limits.
Xanthophylls are considered safe for human consumption within the recommended dietary intake levels, but high doses may cause side effects like carotenodermia (yellowing of the skin).
a. Regulatory Status
(1) Food and feed applications
In the United States, the Food and Drug Administration (FDA) generally considers xanthophylls to be safe (GRAS) for use as food additives and ingredients.The FDA has established specific regulations and guidelines for the use of lutein in food, including maximum allowable levels and labelling requirements. Xanthophylls are also approved for use as animal nutritional feed additives with specific regulations for use in different animal species.
(2) Dietary Supplements
In the United States, lutein supplements are regulated as dietary ingredients under the Dietary Supplement Health and Education Act (DSHEA). Manufacturers of luteophyll supplements must comply with Good Manufacturing Practices (GMP) and labelling requirements set by the FDA. In the European Union, lutein supplements are regulated under the Food Supplements Directive, which establishes safety, quality and labelling guidelines for lutein supplements.
(3) Cosmetics and Personal Care Products
The use of xanthophylls in cosmetics and personal care products is permitted in various jurisdictions, including the U.S., the EU, and other countries.Regulatory agencies, such as the Cosmetic Ingredient Review (CIR) in the U.S. and the Scientific Committee on Consumer Safety (SCCS) in the EU, evaluate the safety of xanthophylls for use in cosmetic products and provide guidance on their safe concentrations and applications.
b. Safety and Toxicological Considerations:
(1) Toxicity and Adverse Effects
It is generally accepted that lutein can be safely consumed by humans within the recommended dietary intake range.
However, excessive intake of xanthophylls, especially from supplements, may result in carotenoid dermatosis, a harmless condition characterised by yellowing of the skin due to deposition of carotenoid pigments. Allergic reactions to xanthophylls are very rare, but have been reported in some individuals.
(2) Interactions and Contraindications
Xanthophylls may interact with certain medications, such as cholesterol-lowering medications (statins) and anticoagulants (blood thinners), possibly altering their absorption or efficacy.
Individuals with certain medical conditions (such as liver or kidney disease) should consult a healthcare professional before taking xanthophyll supplements.
(3) Regulatory Restrictions and Guidelines
Regulatory agencies have established maximum allowable levels for the use of lutein in food, animal feed and dietary supplements. These limits are based on safety assessments and risk evaluations conducted by regulatory agencies and scientific bodies. These limits are based on safety assessments and risk assessments conducted by regulatory agencies and scientific bodies.
Manufacturers and formulators must follow these guidelines to ensure the safe use of lutein in their products.
