Chitosan

Physical and Chemical Properties

Chitosan is the second most abundant (only next to cellulose) biopolymer and is widely distributed. It is mainly distributed in many lower animals particularly the shells of arthropods such as shrimp, crabs and insects. It is also presented in the cell wall of in lower plants such as algae and fungus. Chitosan can be obtained through the deacetylation of chitin. Under the conditions of 40% NaOH and 100 ℃, chitin is subject to deacetylation reaction and give chitosan. It appears as a white or off-white translucent sheet-like gray solid. It is insoluble in water and alkali, but can be dissolved in most kinds of dilute acid including formic acid, acetic acid and hydrochloric acid. The molecular structure of chitosan is similar to that of the cellulose with the only difference being that the C2-position connects the amino group (-NH2). So it has affinity to the paper fibers, evolving strong ionic bonding and hydrogen bonding. Moreover, the chitosan has film-forming property that can help to improve the surface strength of the paper, thus becoming one of enhancers applied to specialty paper. Chitosan appears as powder state and is tasteless, odorless with its aqueous solution having some spicy sense. Adding chitosan to the food for making soup and accompanied with a certain degree of cooking, frying, baking and other heat treatment will have its structure be not changed. Under the protection of nitrogen gas, even upon being heated to 250 ℃, the decomposition phenomenon does not occur. At room temperature, placing chitosan powder in natural place free of sunshine for preservation of 181d causes no significant changes in aspects including appearance, solubility, and the degree of deacylation. The biscuits supplemented with chitosan, when packaged in a state with the temperature of 40 ℃, the relative humidity of 75% environment for preservation of 80d, have their content of dietary fiber and chitosan remain not changed. The chemical structure of chitin, chitosan and cellulose

Physiological role and efficacy

Chitosan is a dietary fiber with various efficacies such as lowering serum cholesterol, regulation of intestinal flora and reducing blood pressure and other effects. After the human intake of chitosan, fecal analysis has showed that it is hardly digested and absorbed, and therefore belonging to a dietary fiber. Studies have shown that chitosan has some characteristics of dietary fiber, such as water retention, swelling property, adhesion property and difficult for digestion and absorbing, etc. It can promote gastrointestinal peristalsis, adhesion of toxic substances, increase stool volume, lower abdominal and intestinal pressure, improve constipation and prevent colorectal cancer. Chitosan has similar physical and chemical property as gastric mucin with effects of inhibiting gastric acid, anti-ulcer and anti-inflammatory effect. It is an anti-gastric acid polysaccharide with swelling into sticky syrup with adhesion property upon coming across water. It can form protective film in the stomach to reduce the stimulation of gastric acid on the ulcer surface. Food safety: when the dose of chitosan feeding animal reaches 20% of the feed, cases of animal deaths have been reported. It is believed that it is due to the gel formation in animal offal caused by high concentrations of the chitosan that inhibit the nutrient absorption by animal. At present, we need to systematically study the physiological roles of the high viscosity chitosan macromolecules and small molecules of low viscosity as well as conduct long-term chronic toxicology test on the safety and metabolism of the chitosan of clear source. The main resource chitin, chitosan

Antibacterial activity

Chitosan has broad antibacterial activity, but with different concentrations of chitosan having different antibacterial capability. For example, when the chitosan concentration is 0.1%, it can completely inhibit the reproduction of all kinds of fungi Fusarium genus within 8d but this concentration has no effect on Rhizopus, Penicillium, Aspergillus and other fungus. At a concentration of 0.4%, it also has strong inhibitory effect against Escherichia coli, Proteus vulgaris, Bacillus subtilis, and Staphylococcus aureus. In addition, chitosan of different degrees of deacylation have their antibacterial properties being also different with mold of high level of deacylation having strong anti-mold effect. One reason is that the chitosan interacts with the surface portion of mold cells, increasing the cell permeability. Preservatives with chitosan being combined with sodium acetate, adipic acid have more significant antibacterial effect without affecting the flavor of food.Antibacterial effect of chitosan mainly includes the following two mechanisms: one is that chitosan adhere to the cell surface and form a layer of polymer film, preventing the transport of the nutrients into the cells, thus playing the role of antimicrobial sterilization; the other mechanism is that: chitosan enters into the cell body through penetration into the cell body, adhering the anion-containing cytoplasm inside cells and cause flocculation, disrupting the normal physiological activities of cells, thus killing the bacteria. Because the cell wall structure of gram-positive bacteria and gram-negative bacteria are different with the two actions having different effects, so chitosan of different molecular weight has different antibacterial mechanism.The above information is edited by the lookchem of Dai Xiongfeng.

preparation

Chitosan is prepared by a degree of acetylation. Acetyl groups are removed during the deacetylation process and Mw changes due to the depolymerization reaction. There are two processes, that is, the enzymatic process and chemical process, and chitosan is produced by chemical process. It is preferable for large-scale production.Glycosidic bonds are attracted toward acids and alkalis. Chitin is processed homogeneously or heterogeneously. In the homogeneous method, chitin is diffused in concentrated alkali at 25℃ for 3h and allowed to disperse in compressed ice at around 0℃. In the heterogeneous process the chitin is treated with hot high-concentration alkali and then washed with distilled water until the pH is neutral. It is difficult to produce higher deacetylated chitosan. The addition of thiophenol as a catalyst during the process would minimize the degradation by trapping oxygen and enhance the effective deacetylation. The effective deacetylation process of chitin achieves the preparation of chitosan if the alkali concentration is four times greater than the total amino group in the polysaccharide at a temperature around 100℃ for the duration of 1 h. It is recommended to use low concentration alkali and a short contact time between alkali and polymer.Chemical deacetylation has many disadvantages like high energy consumption and environmental pollution problems. An alternative method of enzyme deacetylation has been developed to overcome these drawbacks. Chitin deacetylation enzyme acts as a catalysis to hydrolyze N-acetamide bonds. This enzyme is extracted from the fungi Mucor rouxii, Absidia coerulea, Aspergillus hidulans, and two strains of Celletotrichum lindemuthianum. This enzyme is thermally stable and has a binding affinity toward β-(1, 4)-linked N-acetyl-D-glucosomine polymers. Most of the time the enzyme process is carried out in both batch and continuous culture. In the batch process the Mw of chitosan is lower with respect to time. Moreover, chitosan of higher Mw is obtained in a specific culture even though the yield is comparatively low.

Production Methods

Chitosan is manufactured commercially by chemically treating the shells of crustaceans such as shrimps and crabs. The basic manufacturing process involves the removal of proteins by treatment with alkali and of minerals such as calcium carbonate and calcium phosphate by treatment with acid. Before these treatments, the shells are ground to make them more accessible. The shells are initially deproteinized by treatment with an aqueous sodium hydroxide 3–5% solution. The resulting product is neutralized and calcium is removed by treatment with an aqueous hydrochloric acid 3–5% solution at room temperature to precipitate chitin. The chitin is dried so that it can be stored as a stable intermediate for deacetylation to chitosan at a later stage. NDeacetylation of chitin is achieved by treatment with an aqueous sodium hydroxide 40–45% solution at elevated temperature (1108℃), and the precipitate is washed with water. The crude sample is dissolved in acetic acid 2% and the insoluble material is removed. The resulting clear supernatant solution is neutralized with aqueous sodium hydroxide solution to give a purified white precipitate of chitosan. The product can then be further purified and ground to a fine uniform powder or granules. The animals from which chitosan is derived must fulfil the requirements for the health of animals suitable for human consumption to the satisfaction of the competent authority. The method of production must consider inactivation or removal of any contamination by viruses or other infectious agents.

benefits

Chitosan is a fibrous substance that might reduce how much fat and cholesterol the body absorbs from foods. It also helps blood clot when applied to wounds.

Pharmaceutical Applications

Chitosan is used in cosmetics and is under investigation for use in a number of pharmaceutical formulations. The suitability and performance of chitosan as a component of pharmaceutical formulations for drug delivery applications has been investigated in numerous studies. These include controlled drug delivery applications, use as a component of mucoadhesive dosage forms, rapid release dosage forms, improved peptide delivery, colonic drug delivery systems, and use for gene delivery. Chitosan has been processed into several pharmaceutical forms including gels, films, beads, microspheres, tablets, and coatings for liposomes. Furthermore, chitosan may be processed into drug delivery systems using several techniques including spray-drying, coacervation, direct compression, and conventional granulation processes.

Safety

Chitosan is being investigated widely for use as an excipient in oral and other pharmaceutical formulations. It is also used in cosmetics. Chitosan is generally regarded as a nontoxic and nonirritant material. It is biocompatible with both healthy and infected skin. Chitosan has been shown to be biodegradable. LD50 (mouse, oral): >16 g/kg

storage

Chitosan powder is a stable material at room temperature, although it is hygroscopic after drying. Chitosan should be stored in a tightly closed container in a cool, dry place. The PhEur 6.5 specifies that chitosan should be stored at a temperature of 2–88℃.

Incompatibilities

Chitosan is incompatible with strong oxidizing agents.

Regulatory Status

Chitosan is registered as a food supplement in some countries.

Biomedical Attributes

Chitosan, derived from chitin, possesses desirable biomedical attributes. It is considered one of the most ideal antibacterial materials due to its inherent antibacterial properties, wide source, and high yield.

Chemical Composition and Properties

Chitosan is a copolymer of glucosamine and N-acetyl glucosamine, derived from chitin. It is composed of varying amounts of (尾1鈫?4) linked residues of N-acetyl-2 amino-2-deoxy-D-glucose (glucosamine) and 2-amino-2-deoxy-D-glucose (N-acetyl-glucosamine) residues. Chitosan is soluble in aqueous acidic media via primary amine protonation.
Reactive groups in chitosan include the primary amino group (C2) and primary and secondary hydroxyl groups (C6, C3), allowing for various modifications and producing polymers with new properties.

Sources and Production

Chitosan is mainly derived from crustaceans, especially crab, prawns, and shrimp shells, which are readily available as waste from the food processing industry. Commercial chitosan samples were historically produced from the chemical deacetylation of chitin from crustacean sources, but chitosan from fungi is gaining interest, particularly due to vegan demands.

Market and Industrial Applications

In 2019, the global chitosan market size was valued at USD 6.8 billion. Chitosan serves as a raw material for a wide range of products used in food, medical, pharmaceutical, health care, agriculture, industry, and environmental pollution protection.

Solubility and Derivatives

The solubility of chitosan depends on the acetylation degree and molecular weight.
Chitosan oligomers are soluble over a wide pH range, while samples with higher molecular weight are only soluble in acidic aqueous media.
Many chitosan derivatives with enhanced solubility have been synthesized to overcome limitations in neutral physiological conditions.

Biological Activities and Health Benefits

Chitosan exhibits inhibitory effects on bacteria, fungi, and tumor cells. It can induce apoptosis in tumor cells and enhance immune function by promoting the proliferation of T lymphocytes. Chitosan also has reported effects on lowering blood pressure and cholesterol, inhibiting fat absorption, promoting small intestine peristalsis, and improving immunity.

Applications and Formulation

Chitosan can chemically react with organic reagents and be prepared into various shapes, such as sponge materials, nanoparticles, and gel particles. It is utilized in conventional methods for various applications due to its versatility and ability to form different formulations.

General Description

Chitosan is a linear amino polysaccharide composed of approximately 20% β1,4-linked N-acetyl-D-glucosamine (GlcNAc) and approximately 80% β1,4-linked D-glucosamine (GlcN) that is prepared by the partial deacetylation of chitin in hot alkali.