After cellulose, chitin is the most widespread biopolymer in nature. Chitin and its derivatives have great economic value because of their biological activities and their industrial and biomedical applications. It can be extracted from three sources, namely crustaceans, insects and microorganisms. However, the main commercial sources of chitin are shells of crustaceans such as shrimps, crabs, lobsters and krill that are supplied in large quantities by the shellfish processing industries.
Extraction of chitin involves two steps, demineralisation and deproteinisation, which can be conducted by two methods, chemical or biological. The chemical method requires the use of acids and bases, while the biological method involves microorganisms.
Although lactic acid bacteria are mainly applied, other microbial species including proteolytic bacteria have also been successfully implemented, as well as mixed cultures involving lactic acid-producing bacteria and proteolytic microorganisms. The produced lactic acid allows shell demineralisation, since lactic acid reacts with calcium carbonate, the main mineral component, to form calcium lactate.
Enormous amounts of chitin can be found in the bio-sphere; it is the major component of cuticles of insects, fungal cell walls, yeast or green algae. Fungi provide the largest amount of chitin in the soil (6–12 % of chitin biomass, which is in the range of 500–5000 kg/ha). Chitin is also widely present in crab and shrimp shells.
A working estimate for the annual turnover is in the range of 1010 - 1011 tonnes, making chitin one of the most abundant biopolymers. Chitin can be readily obtained by simple extraction. To date, the major source of industrial chitin comes from wastes of marine food production, mainly crustacean shells, e.g. shrimp, crab or krill shells.
In the processing of shrimps for human consumption, between 40 and 50 % of the total mass is waste. About 40 % of the waste is chitin, incrusted with calciumcarbonate and astaxanthin, and containing meat and a small amount of lipid residues. A small part of the waste is dried and used as chicken feed, while the rest is dumped into the sea, which is one of the main pollutants in coastal areas.
The utilization of shellfish waste has been proposed not only to solve environmental problems, but as a waste treatment alternative to the disposal of shellfish wastes. Crustacean shell waste consists mainly of 30–40 % protein, 30–50 % calcium carbonate, and 20–30 % chitin (Table 1), with species and seasonal variations.
Seafood processing and consumption generate each year hundreds of tonnes of shellfish waste, like in Taiwan or Indonesia, whereas in Germany only 22,616 tonnes of shrimp waste is discarded on the seashore. By-products from marine food production, mainly shrimp shells, comprise almost 40 % of total prawn mass and have become a major environmental concern due to their slow degradation. The major components (on dry mass basis) of shrimp waste are proteins, chitin, minerals and carotenoids.
