Ultrasonic Deacetylation of Chitin to Chitosan
Ultrasonic Chitosan Production
Chitosan is obtained by the N-deacetylation of chitin. In conventional deacetylation, chitin is soaked in aqueous alkali solvents (typically 40 to 50% (w/w) NaOH). The soaking process requires high temperatures of 100 to 120ºC is very time-consuming, whilst the yield of chitosan obtained per soaking step is low. The application of high-power ultrasonics intensifies the deacetylation process of chitin significantly and results in a high yield of low-molecular weight chitosan in a rapid treatment at lower temperature. Ultrasonic deacetylation results in superior-quality chitosan which is used as food and pharma ingredient, as fertilizer and in many other industrial applications.
Ultrasonic treatment results in a exceptional degree of acetylation (DA) of chitin lowering the degree of acetylation chitin from DA≥90 to chitosan with DA≤10.
Many research studies confirm the effectiveness of ultrasonic chitin deacetylation to chitosan. Weiss J. et al. (2008) found that sonication improves the conversion of chitin to chitosan drastically. The ultrasonic treatment of chitin comes with significant time savings reducing the required process time from 12-24 hours to a few hours. Furthermore, less solvent is required to achieve a full conversion, which lowers the environmental impact of having to discard and dispose the spent or unreacted solvent, i.e. concentrated NaOH.
Deacetylation of chitin to chitosan is promoted by sonication
UIP4000hdT – 4kW power ultrasonic system
Working Principle of Ultrasonic Chitosan Treatment
High-power, low-frequency ultrasonication (∼20-26kHz) creates acoustic cavitation in liquids and slurries. High-power ultrasound promotes the conversion of chitin to chitosan as the solvent (e.g., NaOH) fragmentes and penetrates the solid chitin particles, thereby enlarging the surface area and improving the mass transfer between solid and liquid phase. Furthermore, the high shear forces of ultrasonic cavitation create free radicals which increase the reactivity of the reagent (i.e. NaOH) during hydrolysis. As a non-thermal processing technique, sonication prevents the thermal degradation producing high-quality chitosan. Ultrasonic shorten processing times required to extract chitin from crustaceans as well as yield chitin (and thus subsequently chitosan) of higher purity compared to traditional processing conditions. For the production of chitin and chitosan, ultrasounds thus has the potential to lower production cost, decrease processing time, allow for a better control of the production process and reduce environmental impact of the process waste.
- Higher Chitosan Yield
- Superior Quality
- Reduced Time
- Lower Process Temperature
- Increased Efficiency
- Easy & Safe Operation
- Environmental-Friendly
Ultrasonic Chitin Decetylation to Chitosan – Protocol
1) Prepare the chitin:
Using crab shells as source material, the crab shells should be thoroughly washed in order to remove any soluble organics and adhering impurities including soil and protein. Afterwards, the shell material must be completely dried (e.g., at 60ºC for 24h in an oven). The dried shells are then ground (e.g. using a hammer mill), deproteinized in an alkaline medium (e.g., NaOH at a conc. of 0.125 to 5.0 M), and demineralized in acid (e.g., dilute hydrochloric acid).
2) Ultrasonic Deacetylation
To run a typical ultrasonic deacetylation reaction, beta-chitin particles (0.125 mm < d < 0.250 mm) are suspended in 40% (w/w) aqueous NaOH at a ratio beta-chitin/NaOH aqueous solution of 1/10(g mL-1), the suspension is transferred to a double-walled glass beaker and is and sonicated by using a Hielscher UP400St ultrasonic homogenizer. The following parameters (cf. Fiamingo et al. 2016) are kept constant when carrying out an ultrasonic chitin deacetylation reaction: (i) ultrasonic probe (sonotrode Hielscher S24d22D, tip diameter = 22 mm); (ii) sonication pulse mode (IP = 0.5sec); (iii) ultrasonic surface intensity
(I = 52.6 W cm-2), (iv) reaction temperature (60ºC ±1ºC), (v) reaction time (50 min), (vi) ratio beta-chitin weight/volume of 40% (w/w) aqueous sodium hydroxide (BCHt/NaOH = 1/10 g mL-1); (vii) volume of beta-chitin suspension (50mL).
The first reaction proceeds for 50min under constant magnetic stirring and is then interrupted by quickly cooling the suspension to 0ºC. Afterwards dilute hydrochloric acid is added to attain pH 8.5 and sample CHs1 is isolated by filtration, extensively washed with deionized water and dried at ambient conditions. When the same ultrasonic deacetylation is repeated as a second step to CHs1, it produces sample CHs2.
Scanning electron microscopy (SEM) images in a magnification of 100× of a) gladius, b) ultrasound-treated gladius, c) β-chitin, d) ultrasound-treated β-chitin, and e) chitosan (source: Preto et al. 2017)
Fiamingo et al. found that the ultrasonic deacetylation of beta-chitin efficiently produces high molecular weight chitosan with a low degree of acetylation neither using additives nor inert atmosphere nor long reaction times. Even though the ultrasonic deacetylation reaction is carried out under milder conditions – i.e. low reaction temperature when compared to most thermochemical deacetylations. The ultrasonic deacetylation of beta-chitin allows the preparation of randomly deacetylated chitosan possessing variable degree of acetylation (4% ≤ DA ≤ 37%), high weight average molecular weight (900,000 g mol-1 ≤ Mw ≤ 1,200,000 g mol-1 ) and low dispersity (1.3 ≤ Ð ≤ 1.4) by carrying out three consecutive reactions (50 min/step) at 60ºC.
High-power ultrasonic processors from lab to pilot and industrial scale.
High-Performance Ultrasonic Systems for Chitosan Production
The fragmentation of chitin and the decetylation of chitin to chitosan requires powerful and reliable ultrasonic equipment that can deliver high amplitudes, offers precise controllability over the process parameters and can be operated 24/7 under heavy load and in demanding environments. Hielscher Ultrasonics product range get you and your process requirements covered. Hielscher ultrasonicators are high-performance systems that can be equipped with accessories such as sonotrodes, boosters, reactors or flow cells in order to match your process needs in an optimal manner.
With digital color display, the option to preset sonication runs, automatic data recording on an integrated SD card, remote browser control and many more features, highest process control and user-friendliness are ensured. Paired with robustness and heavy load-bearing capacity, Hielscher ultrasonic systems are your reliable work horse in production.
Chitin fragmentation and deacetylation requires powerful ultrasound to obtain the targeted conversion and a final chitosan product of high-quality. Especially for the fragmentation of the chitin flakes, high amplitudes and elevated pressures are crucial. Hielscher Ultrasonics’ industrial ultrasonic processors easily deliver very high amplitudes. Amplitudes of up to 200µm can be continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available. The power capacity of Hielscher ultrasonic systems allow for efficient and fast deacetylation in a safe and user-friendly process.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
| Batch Volume | Flow Rate | Recommended Devices |
|---|---|---|
| 1 to 500mL | 10 to 200mL/min | UP100H |
| 10 to 2000mL | 20 to 400mL/min | UP200Ht, UP400St |
| 0.1 to 20L | 0.2 to 4L/min | UIP2000hdT |
| 10 to 100L | 2 to 10L/min | UIP4000hdT |
| n.a. | 10 to 100L/min | UIP16000 |
| n.a. | larger | cluster of UIP16000 |
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Literature/References
- Butnaru E., Stoleru E., Brebu M.A., Darie-Nita R.N., Bargan A., Vasile C. (2019): Chitosan-Based Bionanocomposite Films Prepared by Emulsion Technique for Food Preservation. Materials 2019, 12(3), 373.
- Fiamingo A., de Moura Delezuk J.A., Trombotto St. David L., Campana-Filho S.P. (2016): Extensively deacetylated high molecular weight chitosan from the multistep ultrasound-assisted deacetylation of beta-chitin. Ultrasonics Sonochemistry 32, 2016. 79–85.
- Kjartansson, G., Wu, T., Zivanovic, S., Weiss, J. (2008): Sonochemically-Assisted Conversion of Chitin to Chitosan, USDA National Research Initiative Principal Investigators Meeting, New Orleans, LA, June 28th.
- Kjartansson, G., Kristbergsson, K. Zivanovic, S., Weiss, J. (2008): Influence of temperature during deacetylation of chitin to chitosan with high-intensity ultrasound as a pre-treatment, Annual Meeting of the Institute of Food Technologists, New Orleans, LA, June 30th, 95-18.
- Kjartansson, G., Kristbergsson, K., Zivanovic, S., Weiss, J. (2008): Influence of high-intensity ultrasound to accelerate the conversion of chitin to chitosan, Annual Meeting of the Institute of Food Technologists, New Orleans, LA, June 30th, 95-17.
- Preto M.F., Campana-Filho S.P., Fiamingo A., Cosentino I.C., Tessari-Zampieri M.C., Abessa D.M.S., Romero A.F., Bordon I.C. (2017): Gladius and its derivatives as potential biosorbents for marine diesel oil. Environmental Science and Pollution Research (2017) 24:22932–22939.
- Wijesena R.N., Tissera N., Kannangara Y.Y., Lin Y., Amaratunga G.A.J., de Silva K.M.N. (2015): A method for top down preparation of chitosan nanoparticles and nanofibers. Carbohydrate Polymers 117, 2015. 731–738.
- Wu, T., Zivanovic, S., Hayes, D.G., Weiss, J. (2008). Efficient reduction of chitosan molecular weight by high-intensity ultrasound: Underlying mechanism and effect of processing parameters. Journal of Agricultural and Food Chemistry 56(13):5112-5119.
- Yadav M.; Goswami P.; Paritosh K.; Kumar M.; Pareek N.; Vivekanand V. (2019): Seafood waste: a source for preparation of commercially employable chitin/chitosan materials. Bioresources and Bioprocessing 6/8, 2019.
Facts Worth Knowing
How Does Ultrasonic Chitin Deactylation Work?
When high-power, low-frequency ultrasound (e.g., 20-26kHz) is coupled into a liquid or slurry, alternating high-pressure / low-pressure cycles are applied to the liquid creating compression and rarefaction. During these alternating high-pressure / low-pressure cycles, small vacuum bubbles are generated, which grow over several pressure cycles. At the point, when the vacuum bubbles cannot absorb more energy, they collaps violently. During this bubble implosion, locally very intense conditions occur: high temperatures of up to 5000K, pressures of up to 2000atm, very high heating/cooling rates and pressure differentials occur. Since the bubble collapse dynamics are faster than mass and heat transfer, the energy in the collapsing cavity is confined to a very small zone, also called “hot spot”. The implosion of the cavitation bubble also results in microturbulences, liquid jets of up to 280m/s velocity and resulting shear forces. This phenomenon is known as ultrasonic or acoustic cavitation.
Droplets and particles in the sonicated liquid are impinged by those cavitational forces and when the accelerated particles collide with each other, they get shattered by interparticle collision. Acoustic cavitation is the working principle of ultrasonic milling, dispersing, emulsification and sonochemistry.
For chitin deacetylation, high-intensity ultrasound increases in the surface area by activating the surface and promoting the mass transfer between particles and reagent.
Chitosan
Chitosan is a modified, cationic, non-toxic carbohydrate polymer with a complex chemical structure formed by β-(1,4) glucosamine units as its main component (>80%) and N-acetyl glucosamine units (<20%), randomly distributed along the chain. Chitosan is derived from chitin through chemical or enzymatic deacetylation. The degree of deacetylation (DA) determines the content of free amino groups in the structure and is used to distinguish between chitin and chitosan. Chitosan shows good solubility in moderate solvents such as diluted acetic acid and offers several free amine groups as active sites. This makes chitosan advantageous over chitin in many chemical reactions.
Chitosan is valued for its excellent biocompatibility and biodegradability, non-toxicity, good antimicrobial activity (against bacteria and fungi), oxygen impermeability and film forming properties. In contrast to chitin, chitosan has the advantage of being water-soluble and thereby easier to handle and use in formulations.
As the second most abundant polysaccharide following cellulose, the huge abundance of chitin makes it a cheap and sustainable raw material.
Chitosan Production
Chitosan is produced in a two step process. In the first step, the raw material, such as crustacean shells (ie. shrimp, crab, lobster), is deproteinized, demineralized and purified to obtain chitin. In the second step, chitin is treated with a strong base (e.g., NaOH) to remove acetyl side chains in order to obtain chitosan. The process of conventional chitosan production is known to be very time consuming and cost intensive.
Chitin
Chitin (C8H13O5N)n is a straight-chain polymer of β-1,4-N-acetylglucosamine and is classified into α-, β- and γ-chitin. Being derivative of glucose, chitin is a main component of the exoskeletons of arthropods, such as crustaceans and insects, the radulae of molluscs, cephalopod beaks, and the scales of fish and lissamphibians and can be found in the cell walls in fungi, too. The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. Cellulose is the most abundant polysaccharide of the world, followed by chitin as second most abundant polysaccharide.
Glucosamine
Glucosamine (C6H13NO5) is an amino sugar and an important precursor in the biochemical synthesis of glycosylated proteins and lipids. Glucosamine is naturally an abundant compound that is part of the structure of both polysaccharides, chitosan, and chitin, which makes glucosamine one of the most abundant monosaccharides. Most of the commercially available glucosamine is produced by the hydrolysis of crustacean exoskeletons, i.e. crab and lobster shells.
Glucosamine is mainly used as dietary supplement where it is used in the forms of glucosamine sulfate, glucosamine hydrochloride or N-acetyl glucosamine. Glucosamine sulfate supplements are administered orally to treat a painful condition caused by the inflammation, breakdown and eventual loss of cartilage (osteoarthritis).