Malt and Grains Session
Makoto Kanauchi, Miyagi University Taihaku-ku, Sendai-city, Miyagi, Japan
Co-author(s): Charles Bamforth, University of California, Davis, CA, USA
ABSTRACT: Oxidation promotes off-flavors and haze in beer,
as well as impacting parameters such as wort separation. Increasingly
attention has been drawn to the extent to which oxidative reactions
occur in the brewhouse. Several oxidase and peroxidase enzymes may play a
role in promoting such reactions. Thiol oxidase and oxalate oxidase
levels increase during germination. Thiol oxidase produces disulfide
(-s-s-) bonds in proteins that result in reduced lautering rates. Both
oxidases produce hydrogen peroxide in the reactions they catalyze, and
this reactive species can be the precursor of the even more reactive
hydroxyl. Barley develops a number of peroxidases capable of consuming
peroxide by reaction with polyphenols in the mash; however, some argue
that it would be desirable to preserve such molecules in the beer where
they can function as antioxidants. Our attention has therefore turned to
an enzyme not hitherto studied in barley, namely ascorbate peroxidase.
Levels of this enzyme were highest at 5 days of germination, coinciding
with the highest level of ascorbic acid. Furthermore, enzyme activity
during germination was higher when the grain was sprouted under an
atmosphere of 15% CO2. The optimum pH of the enzyme was 5.5,
and 40% of the activity survived 30 min at 50°C, although the enzyme
would not survive at mash conversion temperatures. The enzyme, a monomer
with a molecular weight of 25,000, is inhibited by iron, mercury, and
copper.
Makoto Kanauchi graduated from the Tokyo University of
Agriculture in Tokyo, Japan, in 1996 and received a Ph.D. degree in
bio-regulation control from that university in 1999. He worked in
Charles Bamforth’s laboratory in the Department of Food Science and
Technology, University of California at Davis (1999–2003). Subsequently,
he was employed at the Institute of Food Science in Fuji Oil Co. Ltd.
in Moriya, Ibaraki, Japan, as a researcher (2003–2005). Since 2005, he
has been at the Department of Food Management, Miyagi University. He has
also been a lecturer in enzymology and alcoholic beverages (mainly
spirits and wine) at the Tokyo University of Agriculture since 2005.
VIEW PRESENTATION 152
