What is Xanthophyll?

Xanthophyll is a phytochemical or accessory pigment that belongs to the “Carotenoids” class. Xanthophylls are light-harvesting protein complexes found in many vascular plants and algae. Antioxidants are abundant in xanthophylls, which protect cells from damage. Xanthophylls are generally linked to chlorophyll molecules in photosynthetic eukaryotes.

Xanthophylls are pigment molecules found inside the photosynthesis complex that shield photosynthetic organisms from the harmful effects of light. We will learn about xanthophyll’s significance, occurrence, molecular structure, types, and functions in this article.

Table of Contents

• Xanthophyll Definition
• Occurrence of Xanthophyll
• Molecular Structure of Xanthophyll
• Types of Xanthophyll
• Functions of Xanthophyll
• Xanthophyll Cycle
• Frequently Asked Questions – FAQs

Xanthophyll Definition

The light-harvesting accessory pigments that function in combination with chlorophyll-a are referred to as xanthophyll. It can absorb light with a wavelength between 425 and 475 nm. Lutein, zeaxanthin, and α- and β-cryptoxanthin are the three main types of xanthophylls. They are antioxidizing chemicals that protect cells from damaging and ageing.

Like anthocyanins, carotenes, and phycobiliproteins, Xanthophylls are classified as accessory pigments in plants. When leaves become orange in the fall season, xanthophylls and carotenic pigments are visible.

Animals cannot make xanthophylls; hence xanthophylls are discovered in them (for example, in the eye) are derived from their diet. Ingested xanthophylls are also responsible for the yellow tint of chicken egg yolks.

Xanthophylls are oxidised carotenoid derivatives. Because they contain hydroxyl groups and are more polar, they are the pigments that will travel the most distance in paper chromatography.

Occurrence of Xanthophyll

Xanthophylls are photochemical cooling agents that deal with the active state of chlorophyll or triplet chlorophyll. They are found naturally in plants and regulate light energy. During the photosynthetic process, triplet chlorophyll develops at a faster rate. Xanthophylls can also be found in the bodies of humans and animals, and they are derived from green vegetation.

Molecular Structure of Xanthophyll

Xanthophylls and carotenes have similar structures since they are both carotenoids; however, xanthophylls have oxygen atoms, whilst carotenes are completely hydrocarbons with no oxygen.

Xanthophylls are far more polar (in molecular structure) to carotenes due to their oxygen content, and they separate from carotenes in several forms of chromatography. When serving as a bridge to generate epoxides, xanthophylls exhibit their oxygen as hydroxyl groups and/or hydrogen atoms replaced by oxygen atoms.

Types of Xanthophyll

Xanthophylls primarily encompass accessory pigments such as Lutein, Zeaxanthin, and Cryptoxanthin.

1. Lutein: This is the most prevalent xanthophyll, a lipophilic component produced by green plants themselves. Lutein can be found in kale, spinach, green apples, kiwi, corn, egg yolk, and other foods. Lutein is found in plants as fatty acid esters, which are made up of one or two fatty acids attached to two –OH groups. Lutein absorbs blue light and hence guards the eye against blue light, which can cause vision problems.
2. Zeaxanthin: This refers to carotenoid alcohols, which are produced naturally by plants and microbes. It works as a non-photochemical quencher. Zeaxanthin is an additional pigment that gives corn, wolfberries, and other plants their distinctive colour. It is made up of two chiral centres. The sources include turnip greens, kale, mustard greens, spinach, and others.
3. Cryptoxanthin: The molecular structure is identical to that of β-carotene, but it also contains a hydroxyl group. In its purest form, cryptoxanthin appears as a red crystalline solid. It also refers to provitamin A, as cryptoxanthin transforms into vitamin A during xanthophyll cycle (retinol).

Functions of Xanthophyll

Xanthophylls are light-harvesting pigments that can also serve as structural entities within the LHC and compounds that protect photosynthetic creatures from the potentially damaging effects of light.

• Light-harvesting: The accessory pigments xanthophylls operate as a photosynthetic light-harvesting compound in algae and vascular plants.
• Dissipation of energy as heat: Xanthophyll assists in photoprotection, or the protection of the photosynthetic system from photo-oxidative degradation in the presence of excessive light, by dissipating energy.

Xanthophyll Cycle

The xanthophyll cycle takes place within the chloroplast’s thylakoid membrane. Interconversion of oxidised carotenoids is facilitated by the xanthophyll cycle. The Diadinoxanthin and violaxanthin cycles are the most common kinds of xanthophyll cycle.

Conversions of pigments from non-energy-quenching to energy-quenching forms are part of the xanthophyll cycle. This strategy limits the light-harvesting antenna’s absorption cross-section and hence the quantity of energy that reaches the photosynthetic reaction centres. One of the key ways to guard against photoinhibition is to reduce the light-harvesting antenna, and changes in xanthophyll cycling occur in a time frame of minutes to several hours.

The xanthophyll cycle in higher plants is dominated by three carotenoid pigments: violaxanthin, antheraxanthin, and zeaxanthin. Violaxanthin is transformed into photoprotective pigments antheraxanthin and zeaxanthin when exposed to light. The enzyme violaxanthin de-epoxidase is responsible for this conversion.

The pigment diadinoxanthin is converted into diatoxanthin (diatoms) or dinoxanthin (dinoflagellates) in the xanthophyll cycle of diatoms and dinoflagellates in the high light.

Related Links:

• What are the plant pigments?
• Is Xanthophyll An Accessory Pigment?
• What Is Difference Between Dyes and Pigment?
• Where Are Carotenoid Pigments Found?