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Valuable new biopolymers from crustacean shells

Huge quantities of seashell waste are thrown away by the shellfish industry while processing crustaceans such as lobsters, crabs and shrimps for human consumption. In the EU alone, more than 250,000 tons of seashell waste are discarded every year. The exoskeleton of crustaceans consists of proteins, calcium carbonate and chitin, a long-chain sugar molecule which could be used to produce valuable building blocks for the polymer industry. In cooperation with eleven international partners, scientists from the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) in Stuttgart have developed a biotechnological process aimed at a sustainable use of this type of waste in the future.

Every year, several million tons of crustacean shells are thrown away. However, many valuable raw materials could be produced from the chitin in the shells and used by the polymer industry to develop a wide range of polymers. © Fraunhofer IGB

Crustaceans are a popular food source for humans due to their taste and their high-protein meat: crabs, shrimps and lobsters are all popular seafoods and are economically very important for the global fishing industry. The animals are processed and their meat sold while the exoskeleton remains are usually discarded. In the EU alone, between 250,000 and 280,000 tons of seashell residues are discarded every year, although the shells could in fact be used quite sustainably. Crustacean shells consist of protein and calcium carbonate, but mostly chitin. Chitin is a long-chain, linear sugar-like polymer consisting of acetylglucosamine, a derivative of glucose. Monomeric acetylglucosamine units could potentially be valuable raw materials for the polymer industry.

Glossary

  • Biotechnology is the study of all processes involving life cells or enzymes for the transformation and production of certain substances.
  • A Catalyst is a substance which selectively accelerates a specific chemical or biochemical reaction without being consumed by the overall reaction.
  • Being lytic is the feature of a bacteriophage leading to the destruction (lysis) of the host cell upon infection.
  • A monomer is the smallest subunit of an oligo- or polymer.
  • Transformation is the natural ability of some species of bacteria to take up free DNA from their surroundings through their cell wall. In genetic engineering, transformation denotes a process which is often used to introduce recombinant plasmids in E. coli, for example. This is a modified version of natural transformation.
  • Biocatalysis is the efficient production of chemical substances by means of microorganisms or enzymes.
  • kb is the abbrevation for kilobase. The unit kb describes the length of DNA or RNA molecules and corresponds with 1,000 bases or base pairs of the nucleic acid.
  • Molecular means: at the level of molecules.
  • Fatty acids are carboxylic acids (organic acids) that often consists of long unbranched carbon chains. They can be either saturated or unsaturated. Fatty acids are part of natural fats and oils.
  • Chitin is a polysaccharide, which is found in the exoskeleton of arthropods and in the cell walls of fungi. The molecule is composed of N-acetyl-D-glucosamine units, which are linked in the beta positions.

Transformation of seashell waste was previously a dirty and toxic process

In Asia, small amounts of this biogenic resource are processed into chitin and its deacetylated form, chitosan, which is used in the biomedical field and as a food additive, after undergoing a chemical process that requires the use of acids and lyes. However, the process is not environmentally friendly and banned in the EU. Neither would it be desirable, as it would need to be highly regulated to guarantee safety and quality, making it too complex and too costly. In addition, European seashell waste contains higher proportions of calcium carbonate, which has so far prevented the cost-effective conversion of chitin into value-added products as the removal of CaCO3 involves a complex demineralisation process.

In order to be able to use this valuable resource, Dr. Michael Hofer from the Stuttgart-based Fraunhofer Institute for Interfacial Engineering and Biotechnology’s (IGB) BioCat subsidiary in the Bavarian city of Straubing has been working on the development of a biotechnological process for recycling seashell waste. From 2011 to 2014, BioCat coordinated a European project called ChiBio in which eleven international partners worked on a sustainable and “green” process to transform the chemical constituents of crustacean shell waste into novel chemical intermediates. “The project ended in 2014. But we are still active in this research area and hope that the EU will provide us with further funding for follow-up projects,” says Hofer.

Successful termination of development process

Dr. Michael Hofer, deputy director of Bio-, Electro- and Chemocatalysis – BioCat, the Fraunhofer Institute for Interfacial Engineering and Biotechnology's (IGB).Straubing branch. Hofer is investigating ways to turn all types of waste into products. © Fraunhofer IGB

The international ChiBio consortium achieved a great deal. The researchers showed that the process used to extract sugar molecules from the seashells works well. Hofer: “We have provided proof of principle, but the process itself is not yet as cost-efficient as we would like it to be. In order to be able to use crustaceans from European seawater, the shell material has to be broken down into its constituent parts. To do this, the IGB’s Irish partners developed a microbiological method that can be used to remove unwanted calcium carbonate and extract chitin and chitosan from the shells. Chitin and chitosan are subsequently broken down into their basic components (acetylglucosamine and glucosamine) using enzymes. The process for doing so was developed by the Fraunhofer IGB’s Department of Molecular Biotechnology in collaboration with a Norwegian research group.

The Fraunhofer researchers also developed a method with which the glucosamines can be turned into biopolymers. The method involves the use of an enzyme cascade, in which several enzymes work sequentially to turn the glucosamine monomers into valuable polymers. “We first turned to nature to see whether we could find some natural chitin-degrading biocatalysts,” says Hofer. “We then adapted the enzymes for our purposes and optimised the polymer yield.” This reaction chain leads to constituents that the chemical industry can use for producing polyamides. Such nitrogen-containing compounds cannot yet be produced from renewable raw materials.

Monomers for the chemical industry

In addition to the method developed at the IGB, a team of scientists from the Industrial Biocatalysis group at the Technical University of Munich developed a method that uses modified yeast cells to degrade chitin and chitosan naturally and store the degradation products as fats and oils from which modified fatty acids can be extracted. “This is another method that can be used to produce biobased polymers,” said Hofer. “What remains after processing in the shellfish companies in addition to the shells, i.e. meat waste and fat residues, can be used for producing biogas. A method for doing so was designed by the IGB’s Department of Environmental Biotechnology and Bioprocess Engineering.”

The different end products that can be produced from crustacean shell waste using the methods developed by the ChiBio partners were given to Evonik Industries, a speciality chemical company headquartered in Germany. “Evonik’s laboratories then focused on ways to turn these monomers into new, biobased polymers,” said Hofer. “This industrial collaboration led to interesting results and a new material with promising properties. However, we only produced enough material for initial tests. In order to further develop the biobased polymer, the chemists need much larger monomer amounts from us. However, at present, this is far too expensive for all the partners involved, which is why the project has been put on the backburner, at least for the time being. However, we are working on an EU proposal for another, relatively major project. If we are granted funds, we will be able to start up testing again by the end of 2016.”

Development of further recycling processes on its way

The IGB’s Department of Molecular Biotechnology is currently working on the use of larger chitin fragments as additives in the textile industry. Hofer and his team are working with an industrial partner to find out whether the shells can be directly, i.e. without modification, ground into powder and subsequently used as fillers for polymer production. If the new proposal is successful, the researchers also want to look into using fungi to produce other types of biopolymers. These new biopolymers could potentially be used as additives in cosmetics and detergents. In this new project, the Fraunhofer IGB will also focus on catalyst development and the conversion of the monomers into valuable products. “That’s where our expertise lies. We want to try to turn waste into all kinds of valuable products to replace products made from fossil fuels such as oil and gas.”

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