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Recent Advances in The Study of Biodegradability of Polyvinyl Alcohol (PVA) Ⅱ

Views: 2     Author: Site Editor     Publish Time: 2023-05-30      Origin: Site


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Recent Advances in The Study of Biodegradability of Polyvinyl Alcohol (PVA) Ⅱ

2. PVA degradase

In the practical application of biodegradation of polyvinyl alcohol, enzymes tend to be easier to use industrially than microbial formulations, and their results tend to be better. This is mainly due to the PVA degradation microorganisms in the process of degradation of polyvinyl alcohol requires nutrients and oxygen, the rate of degradation with the microbial activity and changes, degradation is slow, in the cotton printing and dyeing process is more complex. Enzymes are a good solution to these problems, as the reaction rate is fast and the conditions suitable for enzymatic reaction, i.e. temperature, pH and ionic strength, can be achieved. In order to achieve industrial ease of use, PVA degradation enzymes have to be produced in large quantities. Therefore, the study of the fermentation production, extraction and properties of PVA degradation enzymes, including enzyme application conditions, has been an important breakthrough point in the study of PVA biodegradability.

There are three major classes of PVA degrading enzymes that have emerged, namely PVA oxidases, PVA dehydrogenases and oxidative PVA hydrolases. In recent years, a more specific PVA esterase that can degrade the residual acetate bond on the long chain of low-alcohol PVA has also been discovered.

Suzuki extracted a mixture of PVA oxidase and oxidative PVA hydrolase from the fermentation broth of a strain capable of degrading PVA. PVA oxidase degrades PVA by oxidizing the hydroxyl groups on the long chain of PVA to carbonyl groups and also oxidizing some secondary alcohols, and hydrogen ions and oxygen are produced during the oxidation reaction, which combine with each other to produce hydrogen peroxide.

Watanabe obtained PVA oxidase in the fermentation broth of the strain, and the hydrogen peroxide produced in the degradation of polyvinyl alcohol was generated for some time before the viscosity of the PVA solution decreased. Based on this phenomenon, some researchers have speculated that the oxidation of hydroxyl groups on the long chain of PVA does not occur simultaneously with the chain breakage.

The PVA dehydrogenase produced by Pseudomonas sp. VM15C domesticated by Sakazawa et al. is a membrane-bound enzyme that acts on the hydroxyl group of the polyvinyl alcohol special zone office and undergoes a dehydrooxidation reaction, in the reaction, phenazine methyl sulfate, phenazine ethyl 2 sulfate and 2,6-dichlorophenol indophenol are used as electron acceptors, unlike the previous oxidase, which uses oxygen as electron acceptor to generate hydrogen peroxide, which is toxic to microorganisms. This PVA dehydrogenase also catalyzes the dehydrogenation of secondary alcohols, but not primary alcohols. Shimao found that cytochrome c decreases during the dehydrogenation and oxidation of PVA by PVA dehydrogenase, and genetically engineered the enzyme to have a site that binds to cytochrome c in the gene sequence that may encode the enzyme, leading to the inference that the degradation of PVA is related to the respiratory transport chain.

Researchers at home and abroad have been studying the isolation and purification of PVA degradation enzymes for many years, but since the degradation of PVA involves an enzyme system in which different enzymes work in synergy to completely degrade PVA, and it is very difficult to extract these enzymes simultaneously under the same conditions, coupled with the long culture period of PVA degradation enzyme-producing microorganisms, low activity and low enzyme-producing activity, there is still a long way to go for the mass production of PVA degradation enzymes.

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