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Maart 2017
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Quality of the 2015/2016 season’s
imported and locally produced wheat
S
outh Africa is a net importer of wheat and relies on im-
ports to supply the growing local demand. The quality of all
wheat imported into South Africa is monitored by the
Southern African Grain Laboratory (SAGL).
A subsample of all samples drawn during the previous season by
inspectors of the South African Agricultural Food, Quarantine
and Inspection Services (SAAFQIS) of the Department of Agricul-
ture, Forestry and Fisheries (DAFF) was forwarded to the SAGL for
analysis. The country of origin of the samples were confirmed with
information received from the South African Grain Information
Service (SAGIS).
In total 200 samples were received from nine countries of import.
These samples consisted of nine samples from Argentina, eleven
samples from Australia, 14 samples from Canada, 25 samples from
Germany, 17 samples from Lithuania, 20 samples from Poland,
69 samples from the Russian Federation, five samples from the
Ukraine and 30 samples from the USA. Approximately 82% of the
imported wheat was received at Durban harbour.
Most of the wheat imported to South Africa is blended with local
wheat to obtain a certain milling and baking quality as per indivi-
dual company specifications. Milling companies will blend high-
er and lower quality wheat to obtain the most cost effective grist
formulation that conforms to a specific quality. The main objective
is to supply the most constant quality of flour to their customers
(bakers) as possible, as in the end, consistency is one of the most
important quality parameters.
Towards the end of the production season, it may however become
necessary for milling companies to mill wheat blends consisting
only of imported wheat. Transportation cost is also an important
fact for consideration. The grist formulation of mills situated at
the coast will as a result consist mainly of imported wheat whereas
inland mills will mill a combination of local and imported wheat.
To assist with quality comparisons between local and imported
wheat, the same scope of analysis is used for both sets of samples.
Only twelve of the 200 samples had hectolitre mass values below
the minimum level (77 kg/hl) for grade B1 wheat and only three sam-
ples were below the minimum falling number value (220 seconds).
Seven samples had whole wheat protein levels below the mini-
mum level (10%) for grade B3 wheat.
Except for wheat imported from Australia and Canada, the import-
ed wheat samples tended to have lower Farinograph water
absorptions and shorter development times than local wheat. The
Alveograph distensibility values also tended to be shorter, while
the Mixograms showed a tendency towards longer peak times.
Wheat imported for purposes other than bread baking (e.g. soft
types for biscuit making) is included in this data set.
A total number of 67 composite samples per shipment, per coun-
try of origin were analysed for Aflatoxin G1, B1, G2, B2, Fumonisin
B1, B2, B3, Deoxynivalenol, 15-ADON, Ochratoxin A, Zearalenone,
HT2- and T2-toxin levels.
The mycotoxin residue levels detected on the composite samples
did not raise any major concerns. Most samples tested negative
for all of the mycotoxins mentioned above. On the samples that did
test positive for some of the mycotoxins, Deoxynivalenol was the
most prevalent.
One sample from the USAs Deoxynivalenol level (1 813 μg/kg) was
higher than general internationally acceptable values, but lower
than the national maximum allowable level of 2 000 μg/kg for cere-
als intended for further processing. This sample also tested higher
(215 μg/kg) than the maximum European Union (EU) level of
100 μg/kg for Zearalenone. The highest average mycotoxin levels
were found on samples from the USA.
South African wheat
The national whole wheat protein average of 12,8% is the highest
since the 2004/2005 season and can be attributed to the drought
conditions experienced this season. Protein content is generally a
function of the environment (soil and climatic conditions), where
the wheat was grown as well as fertiliser treatment, whereas
protein quality is genetically controlled and depends mostly on the
wheat variety.
The percentages of samples having protein contents exceeding
13%, increased significantly from 16,4% and 18,3% in the previous
two seasons to 43,2% this season. Contrary to expectations based
on previous experience, the winter rainfall areas did not have the
lowest whole wheat protein average (12,8%) this season. This po-
sition was taken by the irrigation areas, with an average of 12,6%.
The production regions in the Free State Province, reported the
highest average protein content (13,2%) as in previous seasons.
Grade B1 wheat in the Free State Province amounted to 52%
(48% in the previous season). In the irrigation areas 60% (46% in
the previous season) of the wheat graded as B1 and in the West-
ern Cape Province 37% graded as B1 (8% in the previous season).
The increase in the number of samples graded B1 this season, can
be attributed to the increase in protein levels observed over all of
the wheat production areas, especially the Western Cape.
Determination of the protein content is done by means of the
Dumas combustion analysis technique. The sample is combusted
at high temperature (1 100°C) in pure oxygen which sets nitrogen
free, which is then measured by thermal conductivity detection.
The total nitrogen content of the sample as determined, is convert-
ed to equivalent crude protein by multiplication with a factor of
5,7 to obtain the protein content. This factor is based on the amino
acid composition of the proteins in wheat as well as the varying
levels of non-protein nitrogen present in wheat.
Drought conditions, as already mentioned, can result in an increase
of the protein content of a wheat kernel, which is advantageous
to the producer selling the wheat. A combination of water stress
and high temperatures during specific grain filling stages of the
wheat plant, can however influence plant metabolic processes and
wheat quality to varying extents, leading to changes in the protein
composition and size distribution of starch granules which will in
turn affect baking quality.
RELEVANT
JOLANDA NORTJÉ,
laboratory manager, The Southern African Grain Laboratory NPC