Malt and Grains Session
Aaron Macleod, Canadian Grain Commission, Winnipeg, Manitoba, Canada
Co-author(s): John O’Donovan and Kelly Turkington, Agriculture and
Agri-Food Canada, Lacombe, AB, Canada; Michael Edney, Canadian Grain
Commission, Winnipeg, MB, Canada
ABSTRACT: The fermentability of malt wort is dependent on
providing an adequate supply of the amino acids necessary for yeast
metabolism. In addition to supplying the required amounts of total free
amino nitrogen, the relative concentrations of individual amino acids
must also be considered given their differences in absorption and use by
the yeast. It is unclear how amino acid composition of wort is affected
by factors such as cultivar, nitrogen application, and growing
environment; factors that are all known to have significant effects on
grain protein levels. In the present study, five Canadian malting barley
varieties (AC Metcalfe, Major, CDC Meredith, Bentley, and Merit 57)
were grown with different nitrogen application rates (0, 30, 60, 90, and
120 kg/ha) producing grain with a range of protein levels. The amino
acid composition of the barley and resulting malt worts was determined
using ultra performance liquid chromatography (UPLC). The proportions of
glutamic acid, proline, and phenylalanine in barley grain were
positively correlated with protein content, whereas the levels of other
amino acids showed a negative correlation with protein content. This
relationship was consistent among all varieties. While total levels of
free amino nitrogen in wort generally increased with barley protein, the
proportions of most essential amino acids such as histidine, lysine,
and leucine, which can not be synthesized by yeast, were negatively
correlated with grain protein. One notable exception was arginine, for
which concentrations increased. Variety also had a significant effect on
the amino acid profile in the grain and wort. Levels of amino acids in
the barley grain of low protein varieties such as Bentley, CDC Meredith,
and Merit 57 were consistent with their protein content. However, this
relationship was not maintained in the resulting worts, likely as a
result of protease activity in the mash. Different brewing practices
require malts with various protein, amino acid, and enzyme levels
depending on gravity and levels of adjunct used. A better understanding
of the relationship between these factors will aid in the development of
new varieties to meet the needs of the modern brewer.
Aaron
MacLeod is a chemist in the Applied Barley Research unit of the Canadian
Grain Commission Grain Research Laboratory. The unit provides quality
assurance for malting barley grown in western Canada and conducts
research on factors affecting malting barley quality and quality
measurement methods. Aaron earned a B.S. degree in chemistry from the
University of Western Ontario. An active ASBC member since 2008, Aaron
has participated in the collaborative study of numerous new methods and
is currently serving on the ASBC Technical Committee.
VIEW PRESENTATION 160