Soil Bioremediation. Группа авторов
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may be applied to degrade various substances such as undesirable contaminants, byproducts, or discarded waste materials.
3.3.1.1 Degradation of Xenobiotics
One of the potential environmental applications for laccases is the bioremediation of contaminated soils, as laccases are able to oxidize toxic organic pollutants, such as various xenobiotics, Polycyclic Aromatic Hydrocarbons (PAHs), chlorophenols, and other contaminants [15, 16]. Phenolic compounds are present in wastes from several industrial processes: coal conversion, petroleum refining, production of organic chemicals, and olive oil production among others. Immobilized laccase was found to be useful in removing phenolic and chlorinated phenolic pollutants [17]. Laccase‐Mediator‐Systems (LMS) has been extensively studied in the oxidation of recalcitrant PAHs, main components of several ship spills. In this sense, laccase is being included in several enzymatic bioremediation programs [18].
Laccase may be applied to degrade plastic waste having olefin units and can be used to degrade polyurethanes. LMS facilitated the degradation of phenolic compounds (environmental hormones) from biphenol and alkylphenol derivatives and also the decomposition of fluorescent brighteners [18].
3.3.1.2 Decolorization of Dyes
The textile industry accounts for most of the dyestuff market and utilizes large volumes of water and chemicals. The chemical reagents used are very diverse in chemical composition, ranging from inorganic compounds to polymers and organic products. Due to their chemical structure, dyes are resistant to fading on exposure to light, water, and different chemicals and most of them are difficult to decolorize due to their synthetic origin [19, 20].
Several dyes are made from known carcinogens like benzidine and other aromatic compounds. Most currently existing processes to treat dye wastewater are ineffective and not economical. Therefore, the use of enzyme laccases seems like an attractive solution due to their potential in degrading dyes of various chemical structure including synthetic dyes currently used in many industries. The use of laccase in the textile industry is growing very fast since, besides decolorizing textile effluents, laccase is used to bleach textiles and even to synthesize dyes [21, 22]. They could also be used for decolorizing the dye‐house effluents that are hardly decolorized by conventional sewage treatment plants.
3.3.2 Effluent Treatment
Laccase enzyme offers several advantages of great interest to biotechnological applications of industrial effluent treatment. In addition to dye‐house effluents, laccases can decolorize wastewaters from pulp mills by removing colored phenolic compounds. This enzyme may also be used to eliminate odors emitted from garbage disposal sites, livestock farms, or pulp mills. In addition to the potential role of such degradation processes for natural attenuation processes in freshwater environments, this enzyme laccase also offers new perspectives for biotechnological applications such as wastewater treatment [18].
3.3.3 Pulp and Paper Industry
In the paper industry, the separation and degradation of lignin in wood pulp are conventionally obtained using chlorine‐ or oxygen‐based chemical oxidants. Laccases have shown to be applicable to the bioremediation of pulp and paper industry waste by effecting direct dechlorination [23]. The oxygen delignification process has been introduced in recent years to replace the polluting chlorine‐based methods. In spite of this new method the pretreatments of wood pulp with laccase can provide milder and cleaner strategies of delignification that also respect the integrity of cellulose. Other uses of laccases for the pulp and paper industry include an improvement in the paper‐making properties of pulp and can be even used for deinking and decolorizing printed papers [23].
3.3.4 Laccases: Biosensors and Biofuel Cells
A biosensor is an integrated biological‐component probe with an electronic transducer, thus converting a biochemical signal into a quantifiable electrical response that detects, transmits, and records information regarding a physiological or biochemical change. Some of the major attributes of a good biosensing system are its specificity, sensitivity, reliability, portability, real‐time analysis, and operation simplicity. Thus, laccases can be applied as biosensors or bioreporters [24, 25]. A number of biosensors containing laccase have been developed for immunoassays, and for determination of glucose, aromatic amines, and phenolic compounds. Laccase catalysis can be used to assay other enzymes. Laccase enzyme covalently conjugated to a biobinding molecule can be used as a reporter for immunochemical (ELISA (enzyme‐linked immunosorbent assay), Western blotting), cytochemical, histochemical, or nucleic acid‐detection assays. The bioreporter applications are of interest in the high‐sensitivity diagnostic field [25].
In addition to biosensors, laccases could be immobilized on the cathode of biofuel cells that could provide power, for example, for small transmitter systems. Fuel cells are very attractive energy sources, particularly at micro‐, mini‐, portable‐, or mobile‐scale, that potentially have higher energy conversion/usage efficiency and lower pollution effect than any of the existing or emerging energy sources [14].
3.3.5 Laccase in Food Industries
3.3.5.1 Wine Stabilization
Laccase is used to improve the quality of drinks and for the stabilization of certain perishable products containing plant oils. In the food industry, wine stabilization is the main application of laccase. Polyphenols have undesirable effects on wine production and on its organoleptic characteristics, so their removal from the wine is very important. Many innovative treatments, such as enzyme inhibitors, complexing agents, and sulfate compounds, have been proposed for the removal of phenolics responsible for discoloration, haze, and flavor changes but the possibility of using enzymatic laccase treatments as a specific and mild technology for stabilizing beverages against discoloration and clouding represents an attractive alternative. Since such an enzyme is not yet permitted as a food additive, the use of immobilized laccase might be a suitable method to overcome such legal barriers as in this form it may be classified as technological aid. So, laccase could find an application in preparation of must and wine, and in fruit juice stabilization [8].
3.3.5.2 Baking Industry
In the bread‐making process the laccase enzyme affixes bread and dough enhancement additives to the bread dough, these result in improved freshness of the bread texture and flavor. Laccase, when added in the baking process, results in an oxidizing effect, and improves the strength of structures in baked products. Laccase imparts many characteristics to the baked products including an improved crumb structure, increased softness, and improved volume [26].
3.4 Conclusion
The laccase enzymes are receiving much attention from researchers around the globe due to their specific nature. The interest in utilizing laccases for many biotechnological and industrial applications has increased rapidly since the discovery of this enzyme in white‐rot fungi. Emerging technologies include selective delignification in the production of cellulosics in pulp bleaching, biosensors, and biofuel, and in the treatment of environmental pollutants and toxicants generated in various industrial processes. Therefore, laccases have been widely studied for various applications, including the bioremediation of soil and contaminated effluents as well as their use in biosensors. This chapter shows that laccase has a great potential application in environmental protection. However, much more research is required to make use of laccases to protect the environment and in other industrial applications.
References
1 1 Illanes, A., Cauerhff, A., Wilson, L. et al. (2012). Recent trends in biocatalysis engineering. Bioresource Technology 115: 48–57. https://doi.org/10.1016/j.biortech.2011.12.050.
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