Laccase Activity

Laccase is a special polyphenol oxidase (EC 1.10.3.2). This enzyme has wide substrate specificity for phenolic compounds. However, its special feature is to oxidise p-diphenols in the presence of oxygen, unlike tyrosinase that is only able to oxidize o-diphenol and to hydroxylate monophenols.

The purpose of this analysis is to investigate upon the quality of the grape berries for wine making. If the berries were infected by the fungus Botrytis cinerea, a parasite*, the musts produced thereafter will present flavour and aroma defects due to changes in sugar and organic acids content, will be more brow than required¹³ and membrane filtration steps in the process may be hindered^13,14,15. However, if this fungus infected the grapes a "fingerprint" - the laccase activity - can detect its presence^16,17. The detection of laccase activity in grapes is automated¹⁷ and routinely performed at "Estação Vitivinícola Nacional", INIA, a Wine and Vine Research Institute in Portugal to decide whether or not the grapes are to be discarded of the wine production line and also how much should the wine producer pay for each lot of grapes.

The velocity of degradation of a pure substrate (syringaldazine, specific for laccase) added to the must coming from the grapes under test, is followed by automated spectrophotometric analysis** of the coloured quinone (red, l_max =525 nm)¹⁶.

Syringaldazine: [N,N' bis(3,5-dimetoxi-4-hidroxibenzilidene) hydrazine]

* The fungus Botrytis cinerea is able to infect vines. Sometimes this infection is induced and controlled to produce special wines in Europe (this mould is known as the "noble rot").

** Laccase is not yet a commercial analytical enzyme (Novo is selling it recently to the textile industry for the oxidation of the dye indigo in the jeans bleaching process). The quality control laboratories have to produce the laccase (from the Botrytis cinerea) in order to calibrate the equipment.