Microalgae, also known as phytoplankton, are tiny plant-like microorganisms that live in various aquatic environments where they form the basis for most food chains.
They first appeared on earth over one billion years ago, making them one of the oldest species of life.
Microalgae are usually made from one single cell or a small number of cells put together in a very simple structure which can quickly grow and multiply into a large biomass rich in nutrients.
Simply put, microalgae are a type of algae.
Algae comprise a group of aquatic organisms that range from single-cell organisms invisible to the human eye (microalgae) to 3-meter-long kelps (macroalgae or seaweed). Even though they are mostly photosynthetic and have similar functions to plants, algae do not have roots or stems. Algae are responsible for producing about 75% of the global supply of oxygen and feeding different aquatic animals.
Micro- and macroalgae come in different shapes, sizes and colours and can be used for different industrial purposes from food and feed to cosmetics and biofuel production. For example, some seaweeds like Nori are common ingredients used in Asian dishes such as sushi. In turn, Spirulina and Chlorella are microalgae species that make popular food supplements.
Most microalgae are photosynthetic organisms. However, depending on the species, microalgae can use autothrophic, heterothropic or mixothrofic growth mechanisms.
Autotrophic algae use solar energy, dioxide carbon and a few nutrients (such as nitrogen and phosphorous) to grow and reproduce. Heterotrophic algae can grow in the dark using sugar or starch and mixotrophic algae can combine both growth mechanisms.
— Microalgae can either be cultivated outdoors in shallow lagoons, raceway ponds or artificial tanks or indoors in bioreactors (closed system of plastic tubes with transparent walls). Usually, closed reactors allow for a more efficient production when compared to open culture systems, however, they are also more expensive and resource demanding.
— Once the algae biomass is grown, it must be harvested, and the tiny microalgae need to be separated from water.
— After harvesting and separation from water, microalgae need to be quickly processed or they risk spoiling. Depending on the final purpose, different techniques can be used to produce protein, lipids or microalgae extracts which can be later used for different products.
Compared to conventional animal and plant sources of protein, microalgae:
— Microalgae protein yield can be 4-15 times higher compared to other plant crops such as wheat, pulse, legumes and soybean. This means that microalgae can produce higher amounts of protein using less time and resources.
— Like plants, most microalgae are photosynthetic organisms that use CO2, water and sunlight to produce energy and oxygen.
However, microalgae can be 10-50 times more efficient in capturing CO2 and sunlight for photosynthesis when compared to plants. More so, microalgae can also be used to treat and recycle wastewaters due to their ability to remove organic compounds and chemicals from water.
—Microalgae require significantly less land to grow compared to livestock and plant crops. Plus, they can grow in non-arable land (land not suitable for agriculture), sparing natural resources necessary to grow food crops for human and animal feed.
Microalgae can also grow in salt water or non-potable water, thus reducing the need for freshwater use.
Microalgae are rich sources of energy, high-quality protein, healthy fats and health promoting compounds. The nutritional value of algae varies according to the species and their growing conditions, which can be tuned in order to obtain an optimal composition of nutrients in a more sustainable way.
Nonetheless, commercialised species present as nutritious ingredients that can be produced in a more sustainable way.
Microalgae can have as much as 60 % of their dry mass as protein content, which is significantly more than those of plant sources such as soybean (38 %), rice (10 %), pea (3 %), or even animal sources like milk (4 %) or eggs (13 %).
Various species provide high-quality protein and particularly Chlorella and Spirulina are considered comparable sources of protein to eggs and soybean.
Algae can accumulate high amounts of fats, particularly polyunsaturated fatty acids (PUFAs) such as omega-3, usually present in oily fish and seafood. Actually, in nature, fish acquire their PUFAs from eating microalgae.
Polyunsaturated fatty acids, such as EPA and DHA, are necessary for a healthy diet and are mainly found in animal-based products, prompting microalgae, the primary producer of these compounds, as a more sustainable source of those nutrients.
Microalgae contain different types of carbohydrates and provide fibres, which are essential components to keep a healthy heart and gut. Some microalgae species are rich in specific polysaccharides and oligosaccharides (like β-Glucans), making them potential prebiotic candidates.
Besides vitamins and minerals, microalgae also contain other bioactive compounds, such as antioxidants (including lycopene, β-carotene, and astaxanthin), which can be beneficial to health.
Microalgae are being studied for their potential to help support healthy aging, a strong immune system and for their antihypertensive and anti-carcinogenic effects.
Microalgae can be used to create ingredients or raw materials for different industrial applications ranging from food and feed production, to biofuel, to health supplements and cosmetics.
Nutrients and bioactive compounds present in microalgae are used as natural additives to increase shelf life and improve texture, colour and nutritional value of different food products. Species such as Chlorella and Spirulina are also used as food supplements available in the form of powders, tablets or capsules.
Proteins, polyunsaturated fatty acids and bioactive compounds from microalgae are used to enrich animal feed offered to many aquatic species, ruminants, pigs and poultry. Particularly, microalgae present as alternative sources of omega-3 oils usually obtained from oily fish to produce foods and feeds.
Algae are rich in lipids and carbohydrates which can be used as feedstock to produce different types of biofuel (fuel made from renewable resources, such as plants or animal waste), including biodiesel, ethanol, biojet fuel and green gasoline.
Algae are rich in bioactive metabolites such as polyphenols, vitamins, bioactive peptides, carotenoids, omega 3 fatty acids used in neutraceuticals development due to their antioxidant and antiviral activities. They are also trending in cosmetic and skin care products due to their rich composition in amino acids, mineral salts and vitamins.
Organic fertilizers from algae are considered potential alternatives to mainstream chemical fertilizers thanks to their rich composition in micro- and micro-nutrients essential to enhance crops growth and yield.
Algae are used as biological agents for water purification due to their ability to remove coliform bacteria and reduce chemical and biochemical pollutants by accumulating them in their cells.