Chitin and Chitosan are bio-polymer compounds that are widely used today, including industry, medicines, agriculture, cosmetics, food and other numerous areas.
Key Properties of Chitin and Chitosan
1. They are biomaterials with a biocompatibility and are involved in bioactivity. In addition, they are biodegradable so they safe to be used in humans, animals and environment.
2. Chitosan is a polymer that has a positive charge. Chitosan solution has both toughness and clarity.
3. Chitin is insoluble in both water and general organic materials, while chitosan is soluble in various organic acids and then can be changed back into its original condition.
4. They can be molded in various ways, such as gels, pallets, colloid fibers and coatings. They have amino and hydroxyl groups and can be chemically reacted to transform into many other substances.
Chitin was first found in 1811 by Henri Bracannot by isolating it from mushrooms. In 1823, this polymer was named as chitin by Odier. This word comes from Chiton in the Greek language meaning the covering. Chitosan was first discovered in 1859 by Rouget by boiling chitin with concentrated sodium hydroxide. When dissolved in iodine and acid, a purple substance was obtained and it was later named as modified chitin. Later, it was renamed as chitosan by Hoppe Seyler.
Chitin is a natural polysaccharide polymer that occurs from 2- acetamido -2-deoy-β -D-glucose and 2- amino-2-deoxy -β – D. – glucose. It differs from other polysaccharide substances because it contains nitrogen with a cellulose-liked structure, but their indifference is that the carbon in the second position of cellulose has hydroxyl group (-OH) while those of chitin has acetamide group (NH-CO-CH3).
Chitin is a long-molecular compound with no charge and has a molecular weight of about 200,000. Its formula is (C8H13NO5)n by containing 6.5 percent hydrogen, 47.3 percent carbon, 6.9 percent nitrogen, and 39.4 percent oxygen. It is insoluble in water. Chitin is found in general living things and mostly found in creatures with shells or solid walls covering their body, such as shrimps, crabs, snails and insects, as well as in the cell walls of fungi, yeast and algae. This compound serves as a structure to protect and strengthen the body structure.
Natural chitin is divided into three types as follows:
1. Alpha chitin has a multi-layer fiber structure that is stacked in different directions and tight making its structure strongest, such as chitin in shrimp shells and crab carapaces.
2. Beta chitin has a multi-layer fiber structure that is stacked in one direction but not as tight as Alpha chitin making its structure less strong, such as chitin in cuttlefish.
3. Gamma chitin is a combination of both Alpha chitin and Beta chitin with a multi-layer fiber structure that is stacked in different directions making its structure less strong, such as chitin in fungi.
Chitosan, also known as deacetylation chitin, is a copolymer of glucosamine and N- acetylglucosamine and contains more than 90 percent glucosamine. It is insoluble in water and is a cationic polysaccharide because it has the -NH2 group at the second position of carbon making it well soluble in acids. Chitosan is a derivative of chitin that can be produced by the reaction with concentrated alkali to eliminate the acetyl group (Deacetylation) in order to obtain smaller molecules and to make it softer so that it can be molded as gels, pellets, fibers or colloids as well as the use in various forms. In addition, chitosan contains amino (-NH2) and hydroxyl groups (-OH), which can react with other substances to become various other derivatives.
Solubility of Chitosan
Chitosan contains many amino groups (polyamine) that are ready to react with organic acids and some inorganic acids and the salt at pH 6.5 will occur. The reaction process is triggered by chitosan’s amine group receiving protons from acids and becoming a polysaccharide with a positive charge (RNH3 +) with a salt of dissolved chitosan, such as acetate, formate, glycolate, lactate, citrate glyoxylate, malate, pyruvate, and ascorbate. Chitosan is insoluble in neutral or alkaline solutions.
Solubility of Chitosan in Acids
1. It is less soluble in acids, such as formic acid, acetic acid, salicylic acid, and propionic acid.
2. It is moderately soluble in acids, such as lauric acid, citric acid, tartaric acid, sulfuric acid, and hydrochloric acid.
3. It is well soluble in acids, such as oxalic acid, succinic acid, and benzoic acid.
Characteristics of Chitosan
1. Degree of deacetylation (DD)
Chitosan occurs with a reaction of its deacetylation (DD) (long polymer containing N-acetyl glucosamine). Thus, the condition of chitosan depends on the degree of deacetylation reaction, which can be measured by the level of deacetylation. The decline of acetyl group in chitosan therefore increases the amino group of glucosamine, which increases the positive charge on the polymer line and causes the increased condition of chitosan. The rating of deacetylation degree of chitosan is represented as percentage, or known as the Percent Deacetylation (% DD). The degree of this deacetylation affects various properties of chitosan.
2. Antimicrobial properties
Chitosan and its derivatives have the ability to inhibit the growth of many species of microorganisms, such as bacteria, yeast and mold. Chitosan has therefore received a tremendous interest in its applications to prevent the deterioration and to extend the storage period of many foods, such as seafood, meats, vegetables, fruits, milks, breads and juices.
3. Formation of film
Chitosan and various kinds of its derivatives can be formed as a film or membrane that is tough, durable and flexible and that does not tear easily. The film is ideal for preventing the loss of water or moisture and for controlling the access of gas. It can be eaten, and is non-toxic and naturally biodegradable.
4. Molecular weight, viscosity and solubility
Chitosan can be produced in a wide range of types, which have different molecular weights and degrees of deacetylation (DD). This provides chitosan with different viscosity and other properties. It is insoluble in water but soluble in organic acids. When experiencing a hydrolysis, this substance will be in the form with a smaller molecular weight and in the form of oligosaccharide that is soluble in water. Solutions prepared from chitosan with a higher molecular weight are very viscous and can not be put to various applications. Therefore, chitosan is decomposed by a physico-chemical process or the enzyme is used to shorten the polymer line that will then result in a smaller molecular weight. Accordingly, it is more effective to be soluble and absorbed, as well as its other properties are improved.
Benefits of Chitin and Chitosan
Currently, both chitosan and chitin are widely utilized, but more applications are involved with chitosan.
1. Medical applications
– Chitosan is a substance with properties that can be used in many medical applications. It can be prepared in gel tablets, sponge films, pellets, capsules and tablets.
– Chitosan and its derivatives are used to prevent tooth decay, such as acelyn glycol-chitin, carboxymethyl-chitin, sulfated chitosan, and phospholilated chitin. These substances can well inhibit the capture and formation of bacteria on the tooth skin that cause tooth decay.
– Chitin or chitosan sulfate can inhibit the blood clotting and release of lipoprotein lipase by applying it in the process of dialysis to prevent blood clotting. It is also used for wound healing and for preventing an infection of the wounds.
2. Agricultural applications
Chitin and chitosan are agriculturally used in many areas, such as:
– They are used to coat the seeds, prevent the insects, diseases and spoilage by microorganisms, and extend the storage life of seeds.
– They are used to accelerate the growth of plants and act as a hormone to stimulate rooting.
– They are used for improving the soils and increasing the nutrients in soils.
3. Medicine applications
Chitosan is used as an ingredient in various products to prevent the degradation of the drugs in the stomach. It serves as a substance to control the release or introduction of drugs into the blood circulatory system.
4. Food industrial applications
– They are used as a supplement that can provide energy and reduce the amount of LDL cholesterols as well as triglyceride fats in the blood. Chitosan will bind to cholesterols so the body cannot or can less absorb it. Human cannot completely digest all chitin and chitosan and therefore they are released out with feces together with excessive cholesterols and fats. Accordingly, chitosan is often used as a food supplement to lose weight, but chitosan can capture fat-soluble vitamins so this may cause a deficiency of these vitamins. In addition, a medical report explains the use of N-acetyl-D-glucosamine to treat osteoarthritis by explaining that osteoarthritis is caused by the corrosion of soft tissues coating the bone connectors. Glucosamine serves as an initial substance in the synthesis of proteoglycan and matrix of cortical bones thereby making these cortical bones thicker.
– Several countries have registered chitin and chitosan as a food additive, including preservative, substance maintaining the flavor and taste, and substance providing the viscosity. In addition, they are used to maintain the quality of agricultural products by coating them on the surface of fruits and vegetables with an appearance of a clear and thin film without any color and odor. Moreover, they can reduce the respiratory rate, production of ethylene gas, and infestation of insects and fungi within these fruits and vegetables. As such, internal atmosphere of fruits and vegetables causes a less change in their skin and the products will be more resistant against acidic conditions, including their color change will be reduced.
– They can prevent microorganisms in foods because they can bind to a cell membrane of microorganisms causing a leakage of proteins and other substances out of the cells and as a result these microorganisms cannot grow and then decrease in their number.
– They can be used as a food packaging film. Using a film made by polyethylene plastic has a disadvantage of causing quicker food spoilage because it contains moisture inside. On the other hand, a film made by chitosan can better extend the food life because it can better transfer the moisture from the food to the outside.
– They can be used as a fruit juice additive. By adding chitosan, it will serve as a fining agent and can control the acidity of the juices.
5. Cosmetic applications
With the properties of chitin and chitosan that can absorb water well and that serve as a thin film covering and protecting the loss of moisture on the skin, as well as they can resist the microorganisms, they are widely used as an ingredient of many cosmetics, such as face powder, soap, toothpaste, shampoo, sunscreen, moisturizer, hair dye, or hair coating lotion.
Chitosan is put in cosmetics for skin and hair. It has a positive charge, making it possible to bind to the negative charge of skin and hair so it is put in cosmetics that contain a natural fruit acid known as alpha hydroxyl acid (AHA). This acid encourages skin to peel off its old skin and produces the new skin, making the skin look more youthful. Regarding the hair treatment, chitosan will form a film covering the hair making the hair remain soft and non-perishable. Medically, both chitin and chitosan are very popular in the medical and pharmaceutical products.
6. Environmental applications
With the properties of chitin and chitosan that can absorb and catch up with organic substances, including fats and heavy metals, they are widely used as a filter or absorbent of pollutants in the wastewater treatment system.
Chitosan can act as a sediment builder by stimulating aqueous suspensions to be reunited with each other into a large hunk. When a very large hunk is obtained, it will cause sediments to fall to the ground below, while a precipitator will act similarly by gripping with the aqueous suspensions and then settling down. Chitosan can perform both functions well because it has amino groups that can be split into many positive charges. As a result, negative charges, such as proteins, dyes, free fatty acids and cholesterols (in the body), can bind to the positive charges of chitosan. Heavy metals with positive charges will bind to electrons of nitrogen in amino group of chitosan causing a chemical bond called complex bond. The experimental results showed that amino group in chitosan can better bind to heavy metals in the water than acetyl group of chitin.
Production of Chitin and Chitosan
Natural chitin is divided into two types: alpha chitin and beta chitin. Crab and shrimp shells contain alpha chitin, while cuttlefish contain beta chitin. Chitin can be found in both plants and animals. Chitosan is produced by using chitin as initial substance, while chitin is produced by using crab and shrimp shells and shellfish because they are cheaper and easy to buy in the food industry. In addition, they are a source of high chitin. Shrimp and crab shells are composed of chitin about 14-30 and 13-15 percent of their dry weight, respectively.
Production Process of Chitin is as follows:
1. Deproteinization is the step of eliminating proteins from shrimp and crab shells with a reaction with 3-5% sodium hydroxide (NaOH) in a temperature range of 80-90 ° C for 2-3 hours. During this step, proteins are removed along with fats and some colors. After removal, it will be thoroughly washed thoroughly before being sent to the next step.
2. Demineralization is the step of removing inorganic substances, such as minerals, in the shrimp and crab shells by reacting with 3-5% HCl at room temperature for 24 hours. During this step, minerals, including remaining proteins and some colors from the protein removal step, are removed in the form of soluble inorganic substances, such as CaCl2, and then become CO2 to vaporize. After removal, it will be thoroughly washed thoroughly before being sent to the next step.
3. Decoloration is the step of removing all pigments or colors. This step may be done before the production of chitosan to produce chitin products to in turn produce chitosan or done after the step of chitosan production process to obtain chitosan products.
This step uses hydrogen peroxide (H2O2) or sodium perchlorate (NaOCl4) as same as in textile bleaching process. However, these substances shorten the molecular chain of chitosan. It is often done in the early stages of the production process. After removal, it will be thoroughly washed before being sent to the next step.
Production Process of Chitosan is as follows:
The production process of chitosan is similar to those of chitin until obtaining pure chitin. Chitin is then used as an initial substance in the production of chitosan by eliminating acetyl group of chitin by reaction with acid hydrolysis. However, this approach is not popular because its effectiveness of removal is still less than the removal by alkali that often uses sodium hydroxide in the reaction. Then, it will be thoroughly washed and dried as a complete product. An effective production process can be considered based on the amount of remaining acetyl groups.