Different Molecular Weights Chitosan Effect
Chitosan has been widely used in agricultural production due to its biocompatibility, biodegradability, non-toxicity and adsorption capacity. It provides an effective method for reducing agricultural pollution and developing green ecological agriculture. Chitosan can be used as plant growth regulator, soil conditioner, fruit and vegetable preservative, seed coating, especially in crop disease management.
Chitosan has relatively broad-spectrum antibacterial properties and can inhibit the growth and reproduction of some fungi, bacteria and viruses, but the inhibitory effect is affected by the molecular weight of chitosan, its physical and chemical properties, and the types of pathogenic bacteria.
Dora Agri tested three different molecular weights of chitosan. (C1=1.5k Da, C2=30k Da, C3=300k Da)
For low molecular weight chitosan (C1), the higher the concentration used, the more small chitosan molecules enter the pathogenic bacteria cells, and the more chitosan molecules can be combined with the pathogenic bacteria DNA and interfere with the DNA structure. So as to more effectively inhibit the growth of pathogenic bacteria.
For the large molecular weight chitosan C2 & C3, as long as the concentration reaches a sufficient concentration to form a dense enough membrane on the surface of the bacteria cells, the best inhibitory effect can be obtained. We found that the most effective and economical antibacterial concentrations of C2 and C3 chitosan were 0.5% and 1%.
Discussion on Chitosan Mechanism
Doraagri’s test results showed that molecular weight is the most important factor affecting the antibacterial properties of chitosan. The antibacterial effect of low molecular weight chitosan is better than that of high molecular weight chitosan.
Low molecular weight chitosan has a certain bactericidal effect because small molecules are more likely to enter the void structure of the cell wall and interfere with the metabolism of cells to achieve the purpose of bactericidal.
High molecular weight chitosan has strong antibacterial and bactericidal effects, and its antibacterial properties are derived from the antibacterial factor -NH+3, and high molecular weight chitosan has good film-forming properties, which can form a sufficiently dense film on the cell surface to prevent nutrient input from bacteria.
The antagonistic ability of low-molecular-weight chitosan is generally more obvious than that of high-molecular-weight chitosan because it has both film-forming properties and is easier to enter into bacterial cells.
This indicates that the regulation of chitosan molecules at the transcriptional level and the inhibition of pathogen growth are the most effective mechanisms for chitosan to inhibit bacteria. It can be seen that the development and utilization of low molecular weight chitosan can be used as one of the effective ways to develop high-efficiency biological pesticides.
Application of Small Molecular Weight Chitosan in Agriculture
Chitosan oligosaccharide (ie low molecular weight chitosan) has better water solubility than chitosan due to its low degree of polymerization. It has good biocompatibility. High molecular weight chitosan can only be dissolved in acidic solution, which greatly limits the application.
Chitosan oligosaccharide has the advantages of low viscosity, good water solubility, and easy absorption by crops, so it has more biological activities and physiological functions and is widely used in agricultural production.
Cos not only has broad-spectrum antibacterial activity but also induces disease resistance of fruits and vegetables to pathogenic infection, thereby inhibiting postharvest disease and reducing rot loss. Cos can also improve storage quality by inhibiting the respiratory metabolism of fruits and vegetables, preventing water loss, maintaining fruit firmness, delaying color change, and delaying the decline of soluble solids, ascorbic acid, and titratable acid.
All chitosan oligosaccharides used in the test come from Dora’s laboratory. Chitosan oligosaccharide was prepared by enzymatic hydrolysis of chitosan with the high-performance enzyme. The best process conditions were as follows: pH value 4.5, temperature 50 ℃, enzyme dosage 100 U/g, and reaction time 3 h. Under this process condition, the chitosan reaction is complete and the energy consumption is the least.
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