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Chemical formula of chitosan
Chitosan ( ) is a linear polysaccharide composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It has a number of commercial and possible biomedical uses.

Manufacture and properties



Chitosan is produced commercially by deacetylation of chitin , which is the structural element in the exoskeleton of crustaceans (crabs, shrimp, etc.) and cell walls of fungi. The degree of deacetylation (%DA) can be determined by NMR spectroscopy, and the %DA in commercial chitosans is in the range 60-100 %.

The amino group in chitosan has a pKa value of ~6.5, thus, chitosan is positively charged and soluble in acidic to neutral solution with a charge density dependent on pH and the %DA-value. This makes chitosan a bioadhesive which readily binds to negatively charged surfaces such as mucosal membranes. Chitosan enhances the transport of polar drugs across epithelial surfaces, and is biocompatible and biodegradable. Purified qualities of chitosans are available for biomedical applications.

Chitosan and its derivatives such as trimethylchitosan (where the amino group has been trimethylated) have been used in non-viral gene delivery. Trimethylchitosan, or quaternised chitosan, has been shown to transfect breast cancer cells; with increased degree of trimethylation increasing the cytotoxicity and at approximately 50% trimethylation the derivative is the most efficient at gene delivery. Oligomeric derivatives (3-6 kDa) are relatively non-toxic and have good gene delivery properties.

Usage

Agricultural & Horticultural use

Natural Biocontrol & Elicitor

In agriculture, chitosan is used primarily as a natural seed treatment and plant growth enhancer, and as a ecologically friendly biopesticide substance that boosts the innate ability of plants to defend themselves against fungal infections. The natural biocontrol active ingredient, chitin/chitosan, are found in the shells of crustaceans, such as lobsters, crabs, and shrimp, and many other organisms including insects and fungi. It is one of the most abundant bio-gradable materials in the world. Degraded molecules of chitin/chitosan exist in soil and water. Chitosan applications for plants and crops are regulated by the EPA and the USDA National Organic Program regulates its use on organic certified farms and crops. EPA approved bio-degradable chitosan products are allowed for use outdoors and indoors on plants and crops grown commercially and by consumers. The natural biocontrol ability of chitosan should not be confused with the effects of fertilizers or pesticides upon plants or the environment. Chitosan active biopesticides represent a new tier of cost effective biological control of crops for agriculture and horticulture.
Day 30: non-treated broccoli vs. YEA!
(chitosan) treated broccoli (Research Trial by Colorado State University)
The biocontrol mode of action of chitosan elicits natural innate defense responses within plant to resist against insects, pathogens, and soil borne diseases when applied to foliage or the soil. Chitosan increases photosynthesis, promotes and enhances plant growth, stimulates nutrient uptake, increases germination and sprouting, and boost plant vigor. When used as seed treatment or seed coating on cotton, corn, seed potatoes, soybean, sugar beet, tomato, wheat and many other seeds it elicits an innate immunity response in developing roots which destroy parasitic cyst nematodes without harming beneficial nematodes and organisms. Agricultural applications of chitosan can reduce environmental stress due to drought and soil deficiencies, strengthen seed vitality, improve stand quality, increase yields, and reduce fruit decay of vegetables, fruits and citrus crops (see photo right). Horticultural applications of chitosan increases blooms, extends the life of cut flowers and Christmas trees. The US Forest Service has conducted research on chitosan to control pathogens in pine trees . and chitosan's ability to increase pine tree resin pitch-out flow by 40% to resist pine beetle infestation.
Chitosan has a rich history of being researched for applications in agriculture and horticulture dating back to the 1980s. By 1989 Bentech Labs patented chitosan salt solutions applied to crops for improved freeze protection or to crop seed for seed priming. Shortly thereafter Bentech's chitosan salt received the first ever biopesticide label from the EPA. Numerous other chitosan patents for plants soon followed. Chitosan applications to protect plants have been used in space as well. NASA first flew a chitosan experiment to protect adzuki beans grown aboard the space shuttle and Mir space station in 1997 (see photo left). NASA results revealed chitosan induces increased growth (biomass) and pathogen resistance due to elevated levels of beta 1-3 glucanase enzymes within plant cells. NASA confirmed chitosan elicits the same effect in plants on earth. Over 20 years of R&D by DuPont/ConAgra Ventures (DCV) and AgriHouse Inc have gone into developing non-toxic low molecular weight chitosan polymer solutions safe enough for broad spectrum agricultural and horticultural use. In 2008, AgriHouse Inc, Denver [Berthoud], Colorado, was granted EPA natural broad spectrum elicitor status for YEA!® Yield Enhancing Agent, a liquid solution containing an ultra low molecular active ingredient of 0.25% chitosan. YEA! is a next generation natural chitosan elicitor solution for agriculture and horticultural and was granted an amended label for foliar and irrigation applications by the EPA in June, 2009. A milliliter of YEA! contains over 14.4 X 10¹³ bio-active low molecular weight chitosan molecules and it is 600 times more effective than common chitosan). Given its low potential for toxicity and its abundance in the natural environment, chitosan does not harm people, pets, wildlife, or the environment when used according to label directions. Agricultural chitosan facts are located on USDA and EPA web sites.

Water Filtration

Chitosan can also be used in water processing engineering as a part of a filtration process. Chitosan causes the fine sediment particles to bind together and is subsequently removed with the sediment during sand filtration. Chitosan also removes phosphorus, heavy minerals, and oils from the water.Chitosan is an important additive in the filtration process. Sand filtration apparently can remove up to 50% of the turbidity alone while the chitosan with sand filtration removes up to 99% turbidity. Chitosan has been used to precipitate caseins from bovine milk and cheese making[88738][88739]

Chitosan is also useful in other filtration situations, where one may need to remove suspended particles from a liquid. Chitosan, in combination with bentonite, gelatin, silica gel, isinglass, or other fining agents is used to clarify wine, mead, and beer. Added late in the brewing process, chitosan improves flocculation, and removes yeast cells, fruit particles, and other detritus that cause hazy wine. Chitosan combined with colloidal silica is becoming a popular fining agent for white wines, because chitosan does not require acidic tannins (found primarily in red wines) to flocculate with.

Industrial use

Scientists have recently developed a polyurethane coating that heals its own scratches when exposed to sunlight, offering the promise of scratch-free cars and other products. The self-healing coating uses chitosan incorporated into traditional polymer materials, such as those used in coatings on cars to protect paint. When a scratch damages the chemical structure, the chitosan responds to ultraviolet light by forming chemical chains that begin bonding with other materials in the substance, eventually smoothing the scratch. The process can take less than an hour.

Marek W. Urban, a scientist working on this project said that the polymer can only repair itself in the same spot once, and would not work after repeated scratches.

Biomedical use

Chitosan's properties allow it to rapidly clot blood, and has recently gained approval in the United States for use in bandages and other hemostatic agents. Chitosan purified from shrimp shells is used in the range of hemostatic products. Chitosan hemostatic products have been shown in testing by the U.S. Marine Corps to quickly stop bleeding and result in 100% survival of otherwise lethal arterial wounds in swine and to reduce blood loss. Chitosan hemostatic products reduce blood loss in comparison to gauze dressings and increases patient survival. Chitosan hemostatic products have been sold to the U.S. Army, who have already used the bandages on the battlefields of Iraqmarker. Chitosan is hypoallergenic, and has natural anti-bacterial properties, further supporting its use in field bandages.

Claimed health benefits

Chitosan is frequently sold in tablet form at health stores as a "fat attractor": It is supposed to have the capability of attracting fat from the digestive system and expelling it from the body so that users can, it is claimed, lose weight without eating less. However, some scientific research suggests that these claims are likely without substance. The FDA has issued warning letters to several companies who make claims that are not supported by reliable scientific evidence to the benefits of chitosan as a fat blocker. At best, unmodified chitosan would remove roughly 10 calories per day from a person's diet. Modified chitosan is claimed to absorb anywhere up to three to six times its weight in fat and oils. Detractors claim that using chitosan may have the deleterious effect of rendering ineffective certain minerals found in foodstuffs and required by the body in order to remain healthy.

Discussion of medical research on chitosan

With the unavailability of specific research studies to support the claims made on chitosan as a revolutionary weight loss supplements, one must be careful on what is fact and what is speculation. The following are conclusions and specific discussion made from researchers, although take note that their specific studies were not given with precise accounts of their experimentation.

It is now generally accepted that soluble dietary fibers increase gastrointestinal lumen viscosity (Edwards, 1990) and delay gastric emptying (Chang, 1983) . Chitosans have specifically been shown to alter bile acid composition, increase neutral sterol excretion and reduce ileal fat digestibility (Fukada, 1991; Maezaki, 1993; Razdan & Pettersson, 1994) . The mechanisms by which chitosans achieve these effects are not fully established, although increased intestinal viscosity and increased bile acid-binding capacity are two proposals currently favored (Furda, 1990) . Since polyglucosamines are the second-most-ubiquitous dietary fiber after cellulose, it is reasonable to assume that much more research regarding the nutritional significance of these important dietary fibers is to be expected (Knorr, 1991) . Chitosan has such characteristics that are associated with a dietary fiber which are assumed to be related to the reductions in cholesterol as well as increases in the excretion of neutral steroids observed in animal experiments (Furda, 1990; Ikeda, 1993; Razdan & Pettersson, 1994) . Chitosan, which is largely deacetylated, contains cationic groups located on the polyglucosamine chain (Sugano, 1993) . Thus, chitosan may have a bile acid-binding capacity, causing entrapment or disintegration of mixed micelles in the duodenum and ileum (Furda, 1990) . This interruption in bile acid circulation would lead to reduced lipid absorption and increased sterol excretion. Chitosan is relatively insoluble in water but is soluble in dilute acids, giving rise to highly-viscous dietary fibers (Furda, 1990) . It has been suggested that viscous dietary fibers such as chitosan inhibit uptake of dietary lipids by increasing the thickness of the intestinal lumen boundary layer, a proposal again supported by numerous animal experiments (Sugano, 1993; Ikeda, 1993) .

External links



See also



Footnotes

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  3. Self-Repairing Oxetane-Substituted Chitosan Polyurethane Networks
  4. Coating makes scratches on cars disappear


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