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Oktober 2018
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Preharvest sprouting research
– 20 years later
P
reharvest sprouting in wheat is
the result of continuous rainfall
just prior to or during harvest time.
The net result of such sprouting is
the formation of excess
alpha
-amylase,
along with other enzymes, which renders
the wheat flour unsuitable for use in food
products.
Until 1997 the wheat industry in South
Africa was characterised by a single market
ing channel and was controlled by a central
ised Wheat Board who fixed wheat prices
and controlled imports and exports. The
deregulation of the Wheat Board in 1998
has led to various changes, including the
introduction of the falling number method,
which is widely used to estimate
alpha
-
amylase activity in wheat grain, as part of
the South African grading regulations.
Wheat producers in South Africa were
confused by this new method which was
included in the quality description of
wheat sold by producers. The test was in
corporated within the South African wheat
grading regulations, without prior testing
or impact studies being performed. Be
fore its incorporation, wheat was indirectly
evaluated for low falling number through
a visual screening test that required that a
25 g wheat sample should not contain
more than 2% sprouted wheat.
Initially a minimum of 250 sec falling num
ber were required for the highest grade. It
soon, however, became obvious that vari
ous factors, other than sprouted wheat,
had an influence on the falling number of
wheat, as numerous reports of low falling
number wheat without visual sprouting
were received throughout the summer rain
fall wheat producing areas of South Africa,
resulting in enormous financial implications
for the producers.
Once the lack of stability of the test was
realised, a 30 sec grace fraction was imple
mented that stipulated that a falling number
minimum of 220 sec is required to obtain
grade B1 to B3, depending on the protein
content and hectolitre mass. A falling num
ber of 200 sec is required for grade 4, with
wheat being downgraded to utility grade if
the falling number is below 150 sec.
Even with the new regulations in place,
producers continued to experience prob
On farm level
Dry land / Irrigation / Western Cape
Seed
Dr Annelie Barnard,
ARC-Small Grain, Bethlehem
Graph 1: An indication of the progress in preharvest sprouting tolerance in dryland wheat
cultivars from 1992 to 2018.
Graph 2: The preharvest sprouting levels of cultivars released for production in the irrigation
areas since 1994.
Graph 3: Cultivars from the winter rainfall area of the Western Cape showing high levels of
preharvest sprouting tolerance.