Victor Abrahamsson (1), Nikoline J. Nielsen (2), Marianne L. Lund (2), MOGENS L. ANDERSEN (2)
(1) Linnaeus University, Kalmar, Sweden; (2) University of Copenhagen, Copenhagen, Denmark
Sulfite is an important antioxidant in beer, which has an important
effect on oxidative stability. A method for sulfite determination in
beer was developed based on formation of adducts with the
maleimide-derived probe ThioGlo® 1 followed by
high-performance liquid chromatography (HPLC) separation and
fluorescence detection. Two peaks corresponding to sulfite derivatives
were observed. HPLC with mass spectrometric detection showed that the
two derivatives had identical mass spectra and confirmed that they were
derived from sulfite. The quantification of sulfite in beer was affected
by matrix effects, which made it necessary to use a matrix-matched
calibration curve. ThioGlo® also forms adducts with thiols
and a peak assigned to co-eluting thiol adducts was also seen in the
HPLC chromatograms. The level of thiols in the beers were quantified as
glutathione equivalents. The role of sulfite and thiols as antioxidants
in beer was tested by addition of the reactive oxygen species hydrogen
peroxide. The levels of sulfite and thiols decreased in parallel upon
addition of increasing amounts of hydrogen peroxide. The decreases in
concentrations were not proportional to the amount of hydrogen peroxide
added. Extensive addition of hydrogen peroxide did not remove all the
thiols, whereas sulfite was completely consumed. The experiment suggests
that some thiols in beer may also protect against oxidation, and that
synergistic effects together with sulfite may be important for the shelf
life of beer.
Mogens L. Andersen is an associate professor. He graduated from the
Department of Chemistry at the University of Copenhagen in 1990, where
he also obtained his Ph.D. degree in 1993 based on studies of mechanisms
of organic electrochemical reactions. In 1996 he began working as an
assistant professor in the Food Chemistry Group, Department of Food
Science, University of Copenhagen, where he now is an associate
professor. His research focuses on using electron spin resonance
spectroscopy for studies of oxidative reactions in foods. This has
included mechanistic studies of radical reactions in beer, meat,
oils/lipids, and other foods. The work has also included mechanistic
studies of antioxidants in foods, as well as development of methods for
early prediction of oxidative stability. He has published 66
peer-reviewed scientific papers.
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