Seaweed is a natural and sustainable ingredient with a lot of different functional biological properties, amongst them protein. Protein are biochemical compounds comprising one or more polypeptides typically folded into a globular or fibrous form that facilitate biological functions in the body.
Although the structure and biological properties of seaweed proteins are still poorly documented, the amino acid compositions of several species have been known for a long time. Habitat – and especially seasonal variation – has an effect on proteins, peptides and amino acids in seaweed. The protein fraction of seaweed varies with the species but is generally low in brown seaweed, <15%. Higher protein contents are recorded for green and red seaweed, up to 40%. These levels are comparable to those found in highprotein vegetables such as soybeans.
Essential Amino Acids
Most seaweed species contain all the essential amino acids and are a rich source of the acidic amino acids, aspartic acid and glutamic acid and in general are higher than those found in terrestrial plants. One bioactive protein present in algae are lectins, which are a structurally diverse group of carbohydrate binding proteins. Marine algal lectins exhibit antibiotic, mitogenic, cytotoxic, anti-nociceptive, anti-inflammatory, antiadhesion and anti-HIV bioactive properties and are currently commercially produced for a variety of purposes.
Peptides are 2-20 amino acid long chains which once a protein is broken down are released and become bioactive and fulfil certain functions in the body. The depsi-peptide kahalalide-F from Bryopsis sp. – a green alga is active in the treatment of lung cancer, tumours and AIDS. Many other bioactive functions have been ascribed to algal peptides. When protein and peptides are broken down to their individual building blocks we have amino acids. The eight essential amino acids (cystine, isoleucine, leucine, lysine, methionine, phenylalanine, tyrosine and valine) cannot be synthesised by animals, nor can they be replaced by other ‘less valuable building blocks.
All essential amino acids are present in brown and red seaweed species; red species feature uniquely high concentrations of taurine – an ingredient found in a well-known energy drink.
Ocean Harvest Technology in association with several universities has already embarked on optimising extracting total protein – finding and isolating bioactive peptides for applications in aquaculture and animal feed.
Why is this important?
Because a global protein crisis is looming. Currently, about 5 million tonnes of fishmeal is produced and used as feed ingredient in livestock and aquaculture. Virtually all fishmeal is used as a high protein ingredient in feed for farmed land animals and farmed fish. The typical inclusion rate for fishmeal in farm animal diets is 1-5% of dry matter, mainly in specialist diets – e.g. for weaner pigs. A typical farmed salmon diet contains 20-30% fishmeal.
In the ten years to 2002, aquaculture expanded worldwide by more than 9% per annum and since then at a slightly slower rate. While the use of fishmeal will consequently increase – improved efficiency and some substitution means this is likely to be at a slower rate.
Nevertheless, fish stocks used for fishmeal are diminishing and prices are rising. A lot of work has taken place on plant protein as replacement; however, often these plant proteins like soya are less suitable for use in aquaculture due to anti-nutritional factors or lower performance. The large fish-feed manufacturers currently purchase more than €1bn in fish protein and oil per year, sourced primarily from South America by harvesting wild fish from around the world.
Two of the biggest financial and environmental costs for these companies and all fish-feed processors are increasing shortage and the spiralling cost of fish protein. It takes 3-4 kg of wild fish (herring, capelin for example) to create 1kg of fish meal. This is a completely unsustainable scenario that has a major negative impact on the ocean environment.
Seaweed protein extracted for example by Ocean Harvest Technology has a high purity, comprising over 80% protein in contrast to fishmeal at about 65%. It is also extremely popular amongst aquaculture feed manufacturers because of its excellent amino acid profile.
When large-scale production of seaweeds starts in earnest (e.g. in Ireland), it most definitely could help alleviate the problem currently experienced with fish meal and plant protein replacements. Moreover, seaweed protein is derived from a sustainable marine resource and does not have the stigma of being a food crop. These attributes make seaweed protein an excellent source for use in aquaculture feeds and show great potential for it in the future.