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Crayfish chitin is an important raw material

North American Indians recognized the effect of ground crayfish shells on wounds quite a long time ago. Crayfish shells contain chitin, a long-chain polysaccharide with an antibacterial effect when applied as a plaster, which also helps heavy burn wounds to heal faster as well as preventing scars. The goal of current research is to use chitin for nasal spray vaccinations, thus doing away with the need for needles. In his Konstanz-based Vegafood project office, Dr. Peter May is focused on sustainable breeding of crayfish with the aim of advancing industrial scale chitin research. European noble crayfish shed their skin several times a year, providing research institutions and chitin product manufacturers with access to crustacean carapaces.

Dr. Peter May is working on the establishment of a crayfish breeding facility. © Biolago

European crayfish, and the noble crayfish species in particular, were eradicated in Europe in the mid-20th century due to a disease known as American crayfish plague. Since then, European crayfish consumers have had to import crayfish from other countries, in particular Eastern Europe, the Middle East and Africa. As there are no larger-scale noble crayfish breeding facilities in Germany and Switzerland despite the demand from the catering, pharmaceutical and cosmetics sectors, Dr. Peter May is planning to establish a noble crayfish breeding facility. He plans to construct economically sized 4,500-square-metre basins, and use waste heat to warm the indoor and outdoor basins, and spring and groundwater to maintain high water quality. May envisages using the waste heat produced by a cold store in the vicinity of the future crayfish breeding facility. He is also planning to supply restaurants with crayfish meat, and research institutions, pharmaceutical and cosmetics producers with crayfish skeletons (i.e. the carapaces). “Chitin is also the main component of the exoskeletons of insects and worms and the cell walls of fungi. However, crustacean shells are far more suitable for extracting chitin as they contain much larger amounts of the biopolymer,” May explained.

Japan and USA already provide considerable funding for research into this alternative raw material, which can be used for a broad range of medical purposes. Complex procedures are required to extract chitin from the crustacean shells. The shells are ground and dissolved in sodium hydroxide to remove protein. The powder is then dried and the calcium carbonate (chalk) removed with acid, resulting in chitin, a compound containing carbon, hydrogen and nitrogen. Chitin prevents the growth of fungi and bacteria. It also accelerates wound healing processes. Prawn fishermen have healthy teeth because they chew chitin-containing prawn shells, which counteract the activity of streptococci that causes caries, to name but one example.

Chitosan plaster prevents the formation of scars

Previously abundant in Europe, the number of noble crayfish has dramatically fallen due to a disease known as American crayfish plague. © Tropenhaus Frutigen

Chitin is not readily soluble and needs to be processed before it can be used for medical and other applications. The treatment of chitin with sodium hydroxide leads to acetic acid, and finally to chitosan. “Chitosan contains sugar building blocks that contain nitrogen, is protein-free and is not rejected by the human body. When applied in the form of a plaster, it has an antibacterial effect and also absorbs fluid from wounds that is up to 50 times its own weight,” May explained, adding that the chitosan plaster is eventually dissolved enzymatically in the same way as surgical thread made from chitosan. Even heavy burn wounds can be effectively treated with chitosan, which improves wound healing by preventing the formation of scars.

Chitin also has the potential to do away with needle vaccinations. To this end, researchers are exploring the use of chitosan as a drug delivery system, making use of the biopolymer’s ability to form nanoparticles in aqueous solution. These chitosan nanoparticles are able to cross the nasal mucosa and increase the uptake of pharmaceutically active substances. Vaccinations might in future be given using nasal sprays instead of needles. Especially people with diabetes stand to benefit from such nasal sprays. Another positive property of chitosan is that its strongly positive charge attracts negatively charged ions, thereby binding blood lipids and reducing the risk of cardiac infarction and stroke. “Chitosan also binds heavy metals and can thus contribute to the remediation of soil and the purification of wastewater,” said May.

The planned crayfish breeding facility requires specific conditions

Research and product manufacturing require chitin and hence the raw material from which it is extracted. Up until now, North Sea shrimp, whose shell also contains chitin, have been shipped to other countries where the shells are removed. The shelled shrimp return to Germany several weeks later, but the shells remain in the countries where the shrimp are shelled and disposed of. Peter May got the inspiration for his noble crayfish breeding facility during a visit to Thailand where he headed up a shrimp-breeding project and discovered how hormones and antibiotics were commonly used in shrimp breeding. He decided to try and react against the exposure of crayfish to drugs, insecticides and fungicides and focus on the purity of the crayfish body. “Stress is harmful for crayfish, and affects the quality of their meat and carapaces,” said May who now has many years of experience in aquacultures. He plans to breed crayfish as well as investigating and optimizing breeding conditions. He is currently looking into ways how to breed crayfish that live in symbiotic relationships with fish.

In order to adjust the mating, egg formation and depositing as well as the moulting cycle of the crayfish to what happens in the natural environment, the water temperature needs to be adjusted to each particular development stage of the crayfish. Crayfish deposit their eggs during the winter months at a water temperature of between five and seven degrees Celsius; the carapace develops best in summer at a temperature of between 20 and 22 degrees Celsius. “We are able to speed up the growth of the crayfish by increasing the temperature artificially from May onwards,” said May. He also has to closely monitor the density (= number of crayfish per m2) of the animals. The basins contain between one hundred to 200 hundred thousand crayfish. When too many males are present during the mating season, they will fight with each other.

The crayfish diet consists of dead algae and leaves (30%), plants and mosses (30%) and live animals (40%), especially snails. If everything goes to plan, the young crayfish will moult up to six times a year. Older crayfish only shed two to three times a year. However, not all carapaces should be used for the production of chitin. “The carapaces contain calcium, which the crayfish take from the previous exoskeleton and store it to help the new one to harden,” May explained. Crayfish reach their adult length of 20 centimetres when they are around three years old.

Further information:
Dr. Peter May
Kreuzlinger Str. 47 b
78462 Konstanz
Tel.: +49 (0)7531/ 2 66 28
Fax: +49 (0)7531/ 1 62 84
E-mail: dr.may(at)vegafood.de

Website address: https://www.gesundheitsindustrie-bw.de/en/article/news/crayfish-chitin-is-an-important-raw-material