Presenter: Victoria Schiwek, Technische Universität Berlin,
Institute of Food Technology and Food Chemistry, Chair of
Brewing Science, Berlin, Germany
Coauthors: Thomas Kunz, and Frank-Jürgen Methner,
Technische Universität Berlin, Institute of Food Technology
and Food Chemistry, Chair of Brewing Science, Berlin,
Germany
For the prediction of beer flavor stability electron spin resonance
(ESR) spectroscopy has been used for determination of
lag time in the last decades. Previous investigations demonstrated
that the lag-time measurement used up to now falsifies
the results for oxidative flavor stability due to an increasing
pH value during the analysis caused by the spin trap reagent
(PBN). Against this background, a new EAP determination was
developed that excludes falsifications and offers a new index
number for the evaluation of flavor stability: the beverage antioxidative
index (BAX). As a complement to EAP determination,
BAX provides additional information about the interplay
of anti- and pro-oxidative beer ingredients independent of SO2
content and about the consumption rate of the antioxidative
potential during storage. In this study, BAX determination
was used to demonstrate the influence of metal ions, pH, and
Maillard reaction intermediates. Additionally, the correlation
between BAX, beer color as an indicator of Maillard reaction
products in the beer matrices, and formation of typical aging
compounds during storage could be demonstrated. The investigations
clearly demonstrate that lower pH values improve oxidative
beer stability, as reflected by higher EAP, lower radical
generation, and higher BAX values. Iron entry caused by raw
materials and kieselguhr filtration deteriorate oxidative stability,
and polyphenols do not change EAP and BAX significantly.
Furthermore, it could be illustrated that hop ingredients like alpha-
and beta-acids can act as a chelating agents and influence
radical generation significantly and reduce oxidative processes.
It could also be verified that specific intermediate Maillard reaction
products with a reductone/endiol structure formed during
kilning and wort boiling can decrease oxidative stability by the
acceleration of the Fenton-Haber-Weiss reaction system and
can have pro-oxidative properties. Corresponding to this, stronger
generation of specific aging compounds (oxygen indicator)
with higher color and lower BAX is detectable during beer
aging. EAP determination facilitates a genuine examination of
flavor stability. In combination with BAX determination, it is
possible to get a deeper insight into the influences of different
beer ingredients on flavor stability. An additional advantage
of BAX is the indirect determination of SO2 content by linear
regression.
Victoria Schiwek studied pharmaceutical and chemical
engineering at the Beuth University of Applied Sciences from
2002 to 2007. The topic of her diploma thesis was “Optimized
Analytical Methods for the Determination of SO2 in Beer and
Malt.” After graduating, she worked as a chartered engineer
in the field of instrumental analysis, particularly HPLC and
IC, at VLB-Berlin (2007–2009). Since 2010 she has worked as
vice head of laboratory for the Research Institute of Brewing
Science, Technische Universität Berlin (Berlin Institute of
Technology).
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