Laccase

Laccase is a copper-containing enzyme, 1,4-benzenediol oxidase (EC 1.10.3.2), found in higher plants and microorganisms. Laccases are multicopper oxidases of wide specificity that carry out one-electron oxidation of phenolic and related compounds, and reduce O2 to water. The enzymes are polymeric and generally contain one each of type 1, type 2, type 3 copper centers per subunit, where the type 2 and type 3 are close together forming a trinuclear copper cluster.

Laccase is an enzyme that catalyses the oxidation of phenolic compounds such as ortho- and para-diphenols to their corresponding quinones, with the concomitant reduction of oxygen to water. This enzyme is marketed for use in the brewing of beer to prevent the formation of off-flavour compounds, such as trans-2-nonenal. Laccase scavenges oxygen which otherwise would react with fatty acids, amino acids, proteins, and alcohols to form off-flavour precursors.

The enzyme preparation is produced by submerged fermentation of Aspergillus oryzae carrying a gene encoding a laccase from Myceliophthora thermophila. Many fungi and plants produce laccases, and enzymes related to laccase are also produced by bacteria. They form a group of multi-copper proteins of low specifity and catalyse the oxidation of a wide range of both o- and p-quinols, and also aminophenols and phenylenediamine, with the concomittant reduction of oxygen to water. Although the specificity for the electron donor is low, the specificity for the acceptor (oxygen) is essential. Peroxides are not produced in the reaction. The reaction can be described by the chemical equation given in Figure 1.

Figure 1. Mechanism of oxidation catalysed by laccase

The activity of the laccase enzyme preparation is measured by a colorimetric method based on oxidation of the substrate chromophore syringaldazine under formation of tetramethoxy-azo-bismethylene-quinone, and is expressed as laccase Myceliophthora units, or LAMU. The enzyme preparation has a typical activity of 1000 LAMU/g, and has the following composition: total organic solids (TOS), approximately 5.3%; sorbitol, approximately 30%; sodium lactate, approximately 5%; glucose, approximately 3%; glycine, approximately 2%; water, approximately 54.3%; potassium sorbate, 0.2%; and sodium benzoate, 0.2%.

Applications:

The evaluated enzyme preparation is used in the food industry as a processing aid in the brewing of beer to prevent the formation of off-flavour components, such as trans-2-nonenal. During mashing, laccase scavenges oxygen which otherwise would react with sensitive substances to form off-flavour components. The enzyme preparation is to be used at a maximum dosage of 350 g/ton of malt and barley, corresponding to 350 000 LAMU/ton of malt and barley. One ton of malt and barley renders approximately 6000 l of beer.