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Bio- und Umwelttechnologien e. V.

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The GMBU e.V. cooperates with the fermtec GmbH Berlin and the brewery of Landsberg on a research project developing an analysis system for diacetyl and pentanedione in beer matrices.

These vicinal diketones (VDK) rise during the fermentation of beer and are characterized by an intensive and unpleasant flavour even at very low concentrations. The concentration of these substances increases during the fermentation, but the yeast itself degrades them. To avoid a butterscotch flavour of the beer, it is necessary to start the separation of the yeast from the wort in the brewing process, when the concentration of the ketones is on its lowest point. Additionally the precursors of the VDK must be taken into account. Therefore a realtime measurement is required.

A flow injection analysis (FIA) device is planned, which allows an automatized continuous measurement of the analytes during the fermentation without difficult sample preparation. On that account a separation of the key components with a membrane separation module is performed before the start of the analysis. Thus possible interfering substances in the complex beer matrix are eliminated and an optically clear solution is generated. A heating unit in front of the membrane module can be optionally switched on to convert the precursors. Consequently only the diketones (short-term value) or the sum of the diketones and their precursors (long-term value) can be measured.

The central element of the FIA is a flow-through enzyme reactor, in which the analyte is reduced under consumption of NADPH. A fluorometric detection of NADPH is the indirect measurement of the substrate. The co-substrate NADPH is oxidized to NADP+ during the enzymatic conversion of the analyte. Because of this a lower fluorescence signal of the NADPH indicates a higher concentration of diketones.

The enzyme ketoreductase, a form of the alcohol dehydrogenase, is covalently bound to porous glass carriers in the enzyme reactor. This enzyme specifically reduces ketones depending on the presence of NADPH. The flow-through enzyme reactor is exchangeable and is therefore able to be removed from the analysis system so that it can be stored temporarily or replaced if required. The aim is a measurement cycle of 20 to 30 minutes, which is another essential advantage over the elaborate conventional methods. The comparatively quick results make the process attractive for actions during the fermentation and maturing of beer.

A lifetime of at least 6 weeks and a storage time of at least 6 months are intended for the enzyme reactor.