Analytical Session
Frank-Jürgen Methner, Technische Universität Berlin, Department of Biotechnology, Chair of Brewing Sciences, Berlin, Germany
Co-author(s): Thomas Kunz and Christian Müller, Technische
Universität Berlin, Department of Biotechnology, Chair of Brewing
Sciences, Berlin, Germany
ABSTRACT: For the prognosis of the flavor stability of
beer, electron spin resonance (ESR) spectroscopy has been used for
determination of the so-called lag time. Our former investigations
demonstrated that the lag-time measurement used until now falsifies the
results of oxidative flavor stability due to an increasing pH value
during the analysis caused by the spin-trap reagent (PBN). The developed
EAP determination excludes the falsifications due to the use of a
different spin-trap reagent (POBN) in lower concentrations, which
results in a beer matrix dependent, linear correlation between the SO2
content and the EAP value. For this reason, the EAP determination
offers a new beneficial index number for the evaluation of flavor
stability, the beverage antioxidative index (BAX), which provides
additional information about the anti- and pro-oxidative properties of
the beer matrix independent of SO2 content. BAX is affected
by the content of metallic ions, pH value, polyphenols, proteins,
intermediate Maillard reaction products, etc. and gives information
about the consumption rate of the existing antioxidative potential
during storage. In addition, EPR spectroscopy standard analyses
performed according to MEBAK and CFA (continuous flow analyzer) (SO2,
polyphenols, etc.) were used to obtain additional information about the
influences of the different beer ingredients on the radical generation
and oxidative stability by application of the described EAP and BAX
determination. The investigations clearly demonstrate that lower pH
values improve oxidative beer stability, which is reflected by higher
EAP, lower radical generation, and higher BAX values. Iron entry caused
by raw materials and kieselguhr filtration deteriorates oxidative
stability, although polyphenols do not change the EAP and BAX
significantly. Furthermore, it could be illustrated that hop ingredients
like alpha- and beta-acids can act as chelating agents and can
significantly influence radical generation and reduce oxidative
processes. The latest results showed that specific intermediate Maillard
reaction products with reductones/endiol structure formed during
kilning of the malt and wort boiling decreased the oxidative stability
by the acceleration of the Fenton-Haber-Weiss reaction system. In this
context, brewing with raw barley leads to improved oxidative stability,
as indicated by a higher BAX and decreasing radical generation. The
optimized lag-time measurement, called EAP determination, makes an
unbiased examination of flavor stability possible. In combination with
BAX, based on a beer matrix dependent linear correlation of the EAP
value and the SO2 content of a beer, it is possible to obtain
a deeper insight into the influences of different beer ingredients on
flavor stability. An additional advantage of the BAX determination is
the indirect determination of the SO2 content.
Frank-Jürgen
Methner conducted studies in brewing science at Berlin Institute of
Technology (TU) from 1975 to 1981. After the studies, he began working
as an operating supervisor at the Schlösser Brauerei, Düsseldorf. From
1982 to 1986, he was a scientific assistant with teaching duties.
Research projects and Ph.D. thesis, “Aroma Formation of Berliner
Weissbier with Special Focus on Acids and Esters,” were further tasks.
For 18 years, starting in 1987, he held a leading position as a director
at the Bitburger Brauerei, Bitburg, Germany, with responsibilities in
fields such as research and technology, as well as quality assurance.
Beginning with the winter semester 2004/2005 he took over the Chair of
Brewing Science within the Department of Biotechnology at Berlin
Institute of Technology (TU Berlin).
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