Botrytis and laccase activity

LACCASE ACTIVITY

Botrytis cinerea is a weather-driven fungus which causes the grapevine diseases botrytis bunch rot and grey mould, as well as the ‘noble rot’ used for sweet wines. Botrytis produces the enzyme laccase, which in the presence of oxygen can cause serious oxidative spoilage. Early detection of laccase in grapes or juice before fermentation allows winemakers to employ strategic winemaking techniques during grape processing or during and after fermentation. The Managing Botrytis-infected fruit fact sheet details strategies to help to minimise any potential oxidative damage before it occurs.

Qualitative test for laccase activity
A simple bench test can be used to obtain a qualitative result for laccase activity. Sulfur dioxide is added to the sample in question to give a total SO2 concentration of about 60 mg/L. The sample is then poured into two wine glasses (approximately 50 mL of sample in each glass) and each glass is covered with a watch glass or petri dish lid. One sample is placed in a refrigerator, while the other sample is left ‘on the bench’. The samples are examined after 24 hours and compared for any change in colour or quality. If there is laccase activity, the sample left on the bench should be browner than the sample left in the fridge and may have an oily film on the surface of the wine.

After 24 hours:

 

 

 

 

 

 

 

 

 

 

     Fridge sample     Bench sample

Quantitative test for laccase activity
Quantitative determination of laccase activity can be achieved using a number of commercially available test kits. These kits assess laccase activity with a spectrometer, measuring syringaldazine as a purple-coloured oxidation product. AWRI Commercial Services performs a simultaneous quantitative and qualitative analysis for laccase activity in grapes, juice and wine. Laccase results are reported semi-quantitatively in units of laccase activity/mL (U/mL) and as positive/negative for the 24-hour qualitative test.

Laccase activity ranges from 0 in sound fruit, up to 140 U/mL in fully Botrytis-infected fruit. For dry white and red table wines, values greater than 3 indicate that it is likely that there will be some influence of laccase activity. Botrytis also produces glycerol and gluconic acid as major products. Further information is available about gluconic acid testing and glycerol testing.

Grape or juice samples can be submitted fresh or frozen, but juice must be submitted in a plastic container. The presence of free sulfur dioxide and/or ascorbic acid in samples will slow the reactions in the tests and give a false negative or lower apparent laccase activity.

Prices per analysis
Analysis Per sample (excluding GST) Volume required Target response time
Laccase activity $44.10 20 mL/50 g 24 hours

For more information please contact AWRI Commercial Services on (08) 8313 6600 or e-mail commercialservices@awri.com.au