80498-15-3

Laccases are multicopper-oxidases (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) that are able to oxidize phenolic substrates (e.g. 2,6-dimethoxy-phenol), aromatic amines (e.g. 1-hydroxybenzotriazole), or polycyclic aromatic hydrocarbons (e.g. anthracene) . The oxidation of the substrate occurs via a oneelectron reduction and is accompanied by a reduction of molecular oxygen to water.
Most laccases are of fungal origin, but they also occur in bacteria, insects, and plants. Due to the broad substrate range of laccases, their possible industrial usage is widespread. Nevertheless, only few applications have been commercialized up to now, mostly in the textile industry. In the food and feed sector, laccases have been evaluated for different applications, such as the stabilization of beverages, the reduction of off-flavors, the improvement of wheat dough, and the usage of laccases as biosensors in the food processing industry. Off-flavors in wine may occur due to microbial conversion of phenolic compounds present in the wine itself or in the cork stoppers. In a commercial product from Novozymes called Suberase, laccase is used for polymerization of phenolic compounds in the cork, which act as precursors for malodors, such as pentachlorophenol or 2,4,6-trichloroanisol.
In apple juice, addition of laccase reduced the amount of the phenolic offflavors 2,6-dibromophenol, guaiacol, and a-terpineol. Several studies used laccases to increase the stability of apple juices by polymerization of phenols and their subsequent removal by ultrafiltration methods. A positive side effect is the decrease of molecular oxygen in the juice due to its consumption by laccases. Nevertheless, desired phenols might also be oxidized; thus, the sensory attributes and nutritional value might be altered.
The polymerization reactions catalyzed by laccases can also be used to improve the shade of food, such as the coloration of tea-based products. In the bakery industry, laccase might be used together with proteases or xylanases to improve the dough quality. It was proposed that laccases oxidize ferulic acid attached to the arabinoxylan present in cereal flour. The obtained phenolic radicals can undergo a nonenzymatic reaction, resulting in cross-linked feruloylated arabinoxylans. In oat flour-based bread, the usage of laccase increased the loaf-specific volume and decreased the crumb hardness. Contradictory, in another study, laccase alone decreased the specific volume and increased the crumb hardness. A combined usage of laccase with xylanase improved again the oat flour bread properties.

Notclassified

Laccase oxidizes aromatic and nonaromatic compounds. Various compounds are used for detecting laccase production. These include guaiacol, syringaldazine and polymeric dyes like remazol brilliant blue-R. Laccase is involved in lignin degradation and thereby has industrial as well as food applications. Laccase is commonly used for delignification, dye bleaching, paper processing, waste detoxification, textile dye transformation, plant fiber modification and ethanol production.

Lee et al. isolated and identified an extracellular laccase-producing strain of Y. lipolytica from soil. Extracellular laccase (YlLac) was purified by anionexchange and gel filtration chromatography. YlLac is a monomeric glycoprotein with 14 % carbohydrate content and a molecular weight of 67 kDa. It showed a higher catalytic efficiency toward 2,20-Azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (kcat/Km = 19.3 s-1 lM-1) and 2,6-dimethoxyphenol (kcat/Km = 13 s-1 lM-1) than any other reported laccases. This enzyme was able to oxidize phenolic compounds of pretreated rice straw. The use of YlLac for the removal of cellulase inhibitory compounds from biomass slurries is a promising approach for improving the efficiency of biorefineries (Lee et al. 2012).