Chitin is the second most abundant polysaccharide in nature, after cellulose. It is primarily found in the exoskeletons of crustaceans and insects, as well as in bacteria, fungi, and mushrooms Chitosan is derived from chitin through partial deacetylation, a process that removes acetyl groups. The key difference between the two lies in their chemical composition:
- Chitin is mainly composed of N-acetyl-D-glucosamine (GlcNAc) units.
- Chitosan, on the other hand, consists mostly of D-glucosamine (GlcN) units.
Both chitin and chitosan have structures made up of β (1 → 4) glycosidic bonds (as shown in Figure 1). The degree of deacetylation (DD) in chitosan increases as more GlcNAc units are converted into GlcN units
Chitosan has gained significant attention as a functional biopolymer due to its cationic nature, biocompatibility, biodegradability, non-toxicity, and strong adsorption properties.
Key Characteristics of Chitosan
The two main characteristics that define chitosan are:
- Molecular Weight (Mw)
- Degree of Acetylation (DA) or Degree of Deacetylation (DDA)
Based on molecular weight, chitosan is classified into:
- Low molecular weight: <100 kDa
- Medium molecular weight: 100–1000 kDa
- High molecular weight: >1000 kDa
Solubility Challenges and the Need for Chitooligosaccharides (COS)
Chitosan with a high molecular weight and a high degree of polymerization (DP) has low solubility at neutral pH. Additionally, its high viscosity in solution makes it challenging to use in food, cosmetics, agriculture, and healthcare industries.
To improve solubility and molecular uniformity, chitosan is often broken down into oligomers. When chitosan has DP <20 and a molecular weight below 3.9 kDa, it is referred to as chitosan oligomers, chitooligomers, or chitooligosaccharides (COS).
Applications of Chitooligosaccharides
Chitooligosaccharides are produced through chitosan hydrolysis and are water-soluble, making them useful in various applications, including:
- Antimicrobial agents
- Antioxidants
- Anti-tumor compounds
- Agricultural applications