Algal Species Selection
by Dr. Mark Edwards
Algae producers select specific algae strains for valuable compounds grown in the algal biomass. Algal biomass includes primarily lipids, used to produce biofuel, proteins for food, feed and nutraceuticals and starches and carbohydrates that can be made into a litany of products.
Lipids are long carbon chain molecules that store energy for the plant and serve as the structural components of cell membranes. Lipids are oils that make the plant more buoyant so that it moves up the water column towards solar energy. Some algal species are naturally very high in lipid production, e.g. 80% by dry weight, but they grow very slowly. Other species grow very fast and naturally store about 20% lipids but when stressed with nutrient limitation, store about 40% lipids.
Proteins are large organic compounds made of amino acids, arranged in a linear chain connected by peptide bonds. The plant’s genetic code determines the sequence of the amino acids but nutrient limitations may cause changes to the production of amino acids. Most proteins are enzymes that catalyze biochemical reactions and plant metabolism. Other proteins maintain cell shape and provide signaling functions within the plant.
Algae use photosynthesis and solar energy to produce glucose from carbon dioxide. The glucose is stored mainly in the form of starch granules, in plastids such as chloroplasts and amyloplasts. Algae can make water soluble glucose, plant sugar, but it consumes considerable space. Algae adapted the capability to make glucose in the form of starch, complex carbohydrates that are not soluble and store compactly. Starch is the most important carbohydrate in the human diet and algal carbohydrates can substitute for food grain flours such as corn, wheat, potatoes or rice. Starches may also be fermented into a wide variety of alcohols or biofuels.
The path forward based on the Aquatic Species Program and the experience of other research in algal production shows that robust algal species for biofuel production need the following properties:
- Produces high and constant lipid content.
- Grows continuously which requires overcoming the stability problem common to algae cultures.
- Demonstrates high photosynthetic efficiency.
- Grows with seasonal climatic differences and daily changes in temperatures.
- Creates minimal fouling from attachment to sides or bottom of containers.
- Easy to harvest and to extract lipids with soft or flexible cell walls.
Algal growers may select and buy species from culture collections available at the University of Texas, University of Toronto, U.C. Berkeley, University of Copenhagen, the Scottish Marine institute, The Chinese Academy of Sciences , the University of Prague and the World Federation of Culture Collections. Most collections with provide culture sales, composition and pictures. The Algae Gallery at the Smithsonian National Museum of Natural History includes considerable information on algae and links to algal sites.
The composition variation among species varies tremendously. Some algae hold 80% lipids while others produce 60% protein and still others are 92% carbohydrates. Species selection is critical not just for the desired composition but for a host of structure and growth variables that vary widely across species and strains.
When algae are nutrient limited, such as nitrogen, phosphorous or sulfur, they decrease production of essential polyunsaturated fatty acids and may yield lower quality protein with fewer amino acids. Nutrient deprivation may cause algae to increase lipid production but typically slows or halts propagation and growth. Bioengineers are working on algae that increase lipids without nutrient deprivation. Several research labs have created GM algal strains that secrete oil without harvest, enabling continuous production. Avoiding harvest and oil extraction eliminate huge time and cost factors.
Algal varieties offer an almost limitless combination of features. Special attributes are being enhanced through selection screens for naturally occurring organisms, bioengineering and hybridization. Algae experts like Drs. Milton Sommerfeld and Jerry Brand have invested many decades in searching wetlands, lakes and deserts for naturally occurring algae that demonstrate desirable properties. Dr. Bruce Rittmann has worked on genetically modifying algae to produce more oil or other advanced compounds. Many algal producers have worked to hybridize algal strains by cross fertilization in order to maximize desirable growth characteristics, ease of harvest and extraction and desirable compounds.
Each algal species offers a different proportion of lipids, starches and proteins, Table 1. Some algae are high in protein and others are mostly starches or lipids. Variations in culturing may substantially change algal biomass composition.
Table 1. Composition of Various Algae (% of dry matter)
Algal-oils are extremely high in unsaturated fatty acids and various algal-species provide:
- Linoleic acid, an unsaturated omega-6 fatty acid used for soaps, emulsifiers, quick-drying oils and a wide variety of beauty aids. The moisture retention properties are valued skin remedies used for smoothing and moisturizing, as an anti-inflammatory and for acne reduction.
- Arachidonic acid, an omega-6 fatty acid also found in peanut oil. This product moderates inflammation and plays an important role in the operation of the central nervous system.
- Eicospentaenoic acid, an omega-3 fatty acid and gives the same benefits as fish oil, which of course come from algae. Research suggests that EPA may improve brain activity, reduce depression and moderate suicidal behavior.
- Docasahexaenoic acid, an omega-3 fatty acid generally found in fish oil and is the most abundant fatty acid found in the brain and retina. DHA deficiency is associated with cognitive decline and increase neural cell death. DHA is depleted in the cerebral cortex of severely depressed patients.
- Gamma-linolenic acid, an omega-6 fatty acid found in vegetable oil and was first extracted from the evening primrose. It is sold as a dietary supplement for treating problems with inflammation and auto-immune diseases. Research is ongoing on its therapeutic value for cancer to suppress tumor growth and metastasis.
Algal components are commonly found in food ingredients. A normal family that uses normal dairy products may find 70% of the items in their food shopping cart contain algae ingredients. Carrageenans that make up the cell walls of several species of red and brown seaweeds are a family of linear polysaccharides. The carrageenan cell-wall material is a colloid, used as a stabilizer or emulsifier and is commonly present in dairy and bakery products.
Agar. This substance, a polysaccharide, solidifies almost anything that is liquid. Agar is a colloidal agent used for thickening, suspending, and stabilizing. However, it is best noted for its unique ability to form thermally reversible gels at low temperatures. Agar has been used in China since the 17th century and is currently produced in Japan, Korea, Australia, New Zealand, and Morocco.
Today, agar serves scientists globally as a gelatin-like medium for growing organisms in scientific and medical studies. Agar is used extensively in the pharmaceutical industry as a laxative or as an inert carrier for drug products where slow release of the drug is required. Bacteriology and mycology use agar as a stiffening agent in growth media.
Agar also is used as a stabilizer for emulsions and as a constituent of cosmetic skin preparations, ointments, and lotions. It is used in photographic film, shoe polish, dental impression molds, shaving soaps, hand lotions, and in the tanning industry. In food, agar is used as a substitute for gelatin, as an anti-drying agent in breads and pastries and also for gelling and thickening. Agar is used in the manufacture of processed cheese, mayonnaise, puddings, creams, jellies and in the manufacture of frozen dairy products.
Nori, the Japanese word for seaweed, is popular around the world but especially in Asia where it is served with a variety of names such as kombu, wakame, hai dai, laminaria and limu. Scottish cooks call it dulse and the Irish call their product dillisk. Amanori is specifically those foods made from the Porphyra species because it contains essential amino acids, vitamins and minerals. In Korea, Porphyra, is known as kim or lavor. It provides healthy foods that are free of the sugars and fats that are associated with the Western diet.
Wild populations of inland, freshwater algae have been collected and consumed since prehistoric times for their fresh taste and nutrient value. One of the most common, nostoc consists of long beaded chains and forms a gelatinous aggregation of filaments. The individual filaments are microscopic but aggregations occur as globules of all sizes and look similar to grapes.
The microscopic filaments of Spirulina do not form oval globules but often mass into floating clumps that are pushed against the shore by wind. Other algal species appear as threads of free floating masses or filaments clinging to rocks in fast moving water. Spirulina, in powdered form, leads most conventional foods in both total and usable protein. Only poultry and fish are superior with more than 45% usable protein. Spirulina matches meat and dairy products with 30% to 45% protein. Spirulina and nostoc offer more protein by weight than any other vegetable. Earthrise Nutritionals produces 500 tons of edible Spirulina each year at its 100 acre farm in Southern California.
Algal species selection will continue to be a critical issue for algal producers because the right species choice enhances cultivation, harvest, extraction and the value of products produced. Fortunately, the algal species collections offer extensive information on species in their collections and make those species reliably available at modest cost.
Adapted from: Green Algae Strategy: End Oil Imports and Engineer Sustainable Food and Fuel, 2008.