Microalgae are microscopic, photosynthetic organisms that inhabit various aquatic environments, including marine and freshwater systems. They have gained significant attention as a promising source of bioactive compounds with potential applications in various sectors, such as food, pharmaceuticals, cosmetics, and biotechnology. One class of bioactive compounds found in microalgae is carotenoids, which are natural pigments responsible for the vibrant colors of many fruits and vegetables.
Carotenoids are a large group of more than 700 naturally occurring pigments synthesized by plants, algae, and some bacteria and fungi. These compounds play essential roles in photosynthesis, photoprotection, and antioxidant activities. Carotenoids can be divided into two main groups: xanthophylls and carotenes. Xanthophylls are oxygenated derivatives of carotenes and include lutein, zeaxanthin, astaxanthin, and fucoxanthin. Carotenes are hydrocarbons and include β-carotene, α-carotene, and lycopene.
Microalgae produce various types of carotenoids with diverse structures and functions. Some of the most common carotenoids found in microalgae include:
- β-Carotene: This is one of the most abundant carotenoids found in nature and a precursor of vitamin A. It is present in high amounts in Dunaliella salina, a halophilic green alga that can accumulate up to 14% of its dry weight as β-carotene under stress conditions.
- Astaxanthin: This is a red-orange xanthophyll with potent antioxidant properties, responsible for the coloration of salmon, shrimp, crustaceans, and some birds. Haematococcus pluvialis is the richest known source of natural astaxanthin, accumulating up to 4% of its dry weight under stress conditions.
- Fucoxanthin: This is a brown xanthophyll with antioxidant, anti-inflammatory, and anti-cancer properties. It is the primary carotenoid found in brown algae and diatoms, such as Phaeodactylum tricornutum and Isochrysis galbana.
- Lutein: This is a yellow xanthophyll with antioxidant properties and essential for maintaining eye health. It is present in high amounts in some green microalgae, such as Chlorella and Scenedesmus species.
Microalgae possess several advantages over traditional sources of carotenoids, such as plants and animals. Firstly, they can grow rapidly and produce high amounts of carotenoids under controlled conditions, allowing for large-scale production with minimal land use. Secondly, microalgae can synthesize unique carotenoids with novel structures and properties that are not found in terrestrial sources. Lastly, microalgae can be cultivated using waste streams or brackish water, reducing competition for freshwater resources.
To exploit the full potential of microalgae as a source of bioactive compounds, various cultivation strategies have been developed to enhance the production of target carotenoids. These strategies include optimizing growth conditions (e.g., light intensity, temperature, nutrient availability), inducing stress responses (e.g., high light, salinity, nutrient deprivation), and manipulating cultivation modes (e.g., batch, semi-continuous, continuous).
In addition to cultivation strategies, efficient extraction and purification methods are crucial to recover carotenoids from microalgae biomass. Traditional extraction methods involve the use of organic solvents (e.g., acetone, hexane) or mechanical disruption (e.g., bead milling, ultrasonication). However, these methods may have limitations in terms of scalability, environmental impact, or recovery efficiency. Consequently, alternative extraction techniques based on supercritical fluids, enzymes, or ionic liquids have been explored to improve the extraction of carotenoids from microalgae.
In conclusion, microalgae represent a promising source of carotenoids with potential applications in various industries. The development of advanced cultivation and extraction techniques will be crucial to harness the full potential of these versatile organisms for the sustainable production of valuable bioactive compounds.
