P-9
Critical stages of the brewing process for changes in antioxidant activity,
color and flavor. The effect of the malting process on the antioxidant activity of pale and
speciality malts is currently a very active area of research. However, the
contribution of these antioxidants to the beer and the effects of the complete
brewing process on changes in antioxidant activity is less well understood. The
aim of this study was to determine the effect of each stage of the brewing
process for best bitter on the antioxidant activity, color and selected malt
flavor compounds. Antioxidant activity was carried out on unfractionated
samples, low molecular mass (LMM) (<5 kDa) and high molecular mass (HMM) (>5
kDa) fractions, using the 2,2'-azino-bis(3-ethylbenothiazoline)-6-sulfonic acid
radical cation (ABTS (^radical+) scavenging method and ferric reducing
antioxidant power (FRAP) assay. Serial dilution color profiles were constructed
from CIEL*a*b* tristimulus values, and the fate of selected malt flavor
compounds was monitored using gas chromatography-mass spectrometry. Changes in
the serial dilution color profile occurred after boiling, fermentation and
clarification, with the profile after clarification being the same as that at
the end of boiling. The majority of the flavor compounds originating from the
malt were lost during brewing, with 3-methylbutanal, 2-methylbutanal, furfural,
hexanal and E-2-nonenal being found above their odor threshold levels in
the final beer. Both of the antioxidant assays showed that the LMM fraction
contributed the most antioxidant activity (75-90%). The most critical stages
during the brewing process for changes in antioxidant activity as assessed by
both assays were filtration and clarification, with clarification also having a
significant effect on the color of the beer. Several of the other stages
indicated a change in antioxidant activity as assessed by either the ABTS
(^radical+) or FRAP procedure. These included boiling, fermentation, maturation
and pasteurisation. Both filtration and clarification technologies warrant
further investigation for optimisation of antioxidant activity in beer.
Helen Woffenden received a B.Sc. with First Class Honours in Food Science
from the University of Reading, U.K. in 1999. Since 1999, she has been working
for her Ph.D. in the School of Food Biosciences at The University of Reading, in
collaboration with Brewing Research International, on the characterisation of
thermally induced antioxidants during malting and brewing.
HELEN WOFFENDEN (1), Jennifer Ames (1), and Sachin Chandra (2). (1) School of
Food Biosciences, The University of Reading, PO Box 226, Reading, RG6 6AP UK,
and (2) Brewing Research International, Lyttel Hall, Nutfield, Surrey, RH1 4HY,
UK.