What is Chitin?
Chitin is a naturally occurring biopolymer that is found in the shells and exoskeletons of a range of organisms, including shellfish, insects and more.
The term ‘biopolymer’ means that it is naturally occurring (‘bio’) and that it is made up of a long chain of repeating molecules (“polymer”). The molecular structure of chitin is what gives it the many useful properties that make it a crucial component in shells, exoskeletons and even in the cell walls of some fungi.
Chitin is thought to be the second most abundant natural polysaccharide after cellulose, which is a component of plant cell walls. Polysaccharide simply refers to a carbohydrate that is made up of multiple sugar molecules bonded together. The term chitin come from the Greek, ‘khiton’, which was used to refer to a tunic or other forms of coverings.
There are several different types of chitin, distinguished by differences in the arrangement of molecular chains within the biopolymer. These are called alpha, beta and gamma chitin. Alpha chitin has what is referred to as an antiparallel arrangement of the polysaccharide chains, which means that the chains alternate their direction as they stack on top of one another. Beta chitin, on the other hand, has its chains arranged in a parallel formation, meaning all chains are running in the same direction. Finally, gamma chitin has a mixture of parallel and antiparallel chains.
This difference in their molecular arrangement impacts the properties of the chitin, and, as a result, its final uses. Therefore, varying organisms can utilise different chitin arrangements within their morphology; for example, alpha chitin is found in crustaceans, beta chitin is found in squid and gamma chitin in fungi.
What is Chitosan?
Chitin can then also be further processed to produce something called chitosan. This process is called deacetylation and involves the removal of a specific part of the chitin molecules (acetyl groups, hence the deacetylation). The removal of these groups results in a change in the chemical properties of chitosan when compared with chitin. For example, chitin is insoluble in many organic solvents whereas chitosan is soluble in some acidic solutions. As a result, chitosan has different uses and applications than chitin does. In addition to this, the conditions of this conversion process impact how much deacetylation takes place, referred to as the “degree of deacetylation”, which again impacts the properties of the final product.