Liquid nitrogen freezes the cell. It keeps harmful chemicals and natural enzymes ( e.g. nucleases) deactivated due to its very low temperature.
Extraction of high quality DNA from medicinal plants and its purification is difficult because of the presence of large quantities of secondary metabolites, poly-saccharides and proteins such as tannins, alkaloids, and polyphenols. These compounds degrade the quality of DNA by precipitating along with it, thus reducing yield ,Liquid nitrogen plays an important role in obtaining good quality DNA and hence, it has been used extensively for DNA extraction from fresh leaf and or other tissues.
hi Dr.EsraaTahir
https://www.researchgate.net/.../functions_and_use_of_liquid_nitroge...
Chapter Plant Cell Wall Polymers
Kindly check here too..
http://www.nbpgr.ernet.in/Portals/6/DMX/GENOMIC_RESOURCES/DNA%20extraction-Comparison%20of%20methodologies.pdf
Using liquid nitrogen need to use sample immediately after grinding, to prevent DNase from degrade DNA
Liquid nitrogen is used as it has a very low temperature of -176° C which help to pulverize the hard substance of plant and animal tissue to turn into dust. It also help in deactivating the DNAase to digest the DNA .
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