Laccase is a blue copper oxidase that reduces molecular oxygen to water. Laccase oxidizes polyphenols, methoxy-substituted phenols and diamines, but not tyrosine. Oxidation by laccase is an one-electron reaction that generates a free radical.
Laccase is a polyphenol oxidase belonging to the blue oxidase family and is one of the important lignocellulolytic enzymes. Laccase was first discovered in the toxicodendron vernicifluum. Subsequently, it was found that certain fungi also secreted the laccase. Laccase can catalyze the degradation of a variety of aromatic compounds, especially phenols, and is a natural environmentally friendly enzyme. The rational development of the degradation of wood fiber and some polymer compounds by laccase can reduce the use of chemicals, reduce production costs and protect the environment.
The most common method to detect laccase is an intuitive method for producing color change in a short reaction time by using laccase and a specific substance, such as titration method and color changing circle reaction method used with a PDA medium. For example, laccase can react with substances such as syringaldazine, guaiacol, α-naphthol, pyrogallic acid, and citric acid, and rapidly produce substances of a specific color. According to the specific color change reaction of laccase and these substances, it is determined whether the strain produces laccase. The laccase production can be estimated based on the color depth and the color circle size generated in the same time.
Kirk et al. obtained the best laccase production conditions in the fungi fermentation process through extensive research. The basic medium identified in this study has been widely used by researchers. The study found that the type of nitrogen source in the laccase fermentation process cannot significantly affect the laccase production, and the nitrogen dosage is one of the key factors affecting the laccase production. Nitrogen-limited culture can significantly increase the laccase production. Laccase is a copper-containing polyphenol oxidase, so Cu2+ is essential for the synthesis and activity of laccase. Low molecular aromatic compounds similar in structure to lignin or lignin-degraded fragments can also induce and significantly increase laccase production, such as guaiacol, benzyl alcohol, resveratrol, vanillic acid, Tween and so on. Limiting the carbon content can also significantly increase the production of laccase. The French Galliano et al. compared the solid and liquid medium. The lignin degradation in the solid medium was significantly higher than that in the liquid medium by the 14C radiolabeling method, and the amount of laccase produced was 15 times higher.
Laccase has also been widely used in the food industry. Increasing the stability of glucose is a major application of laccase in the food industry. The addition of laccase can improve the stability of the wine, thus reducing the amount of sulfur dioxide used. In addition, laccase can also play a very good role in fruit juice production, because the excessive oxidation of phenols will affect the quality of the product, and laccase can remove phenolic substances such as catechol in juice. Therefore, the fruit juice can be stably clarified without additional clarifying agent.
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