The important role of the ARC-SGI Wheat Quality Laboratory in releasing new cultivars

CHRISSIE MILES, ARC-SMALL GRAIN INSTITUTE, BETHLEHEM

The Agricultural Research Council’s (ARC) Wheat Quality Laboratory is situated at the Small Grain Institute (SGI) outside Bethlehem. This laboratory was started to assist wheat breeders at the ARC-SGI to obtain information regarding potential wheat breeding lines in order to decide whether certain breeding lines can be released as commercial cultivars or not.

Analyses for research purposes take up 95% of the laboratory’s time each year. Wheat producers, co-operations, small milling companies, fertiliser companies and universities also make use of the services rendered by this laboratory, which then accounts for the other 5% of the laboratory’s time.

The ARC-SGI’s three wheat breeding programmes (winter and intermediate wheat for the Free State, spring dry land wheat for the Western Cape and irrigation wheat for the irrigation areas) send wheat samples for quality analyses as early as from the F4 breeding phase.

Sample sizes are still small during the early breeding phases and only limited quality analyses can be performed as to enable the breeders to select only the best possible potential breeding lines at this early breeding phase. As sample sizes increases during advanced breeding phases, more intensive analyses can be performed.

This laboratory is well equipped to determine characteristics as desired by producers as well as the baking and milling industry, which are also the characteristics of importance during the release of new bread wheat cultivars.

These characteristics include:

• Hectolitre mass (test weight), which is indicative of kernel density. Kernels exhibiting higher density indicate higher volumes of flour to be obtained from a certain volume of wheat, which is more profitable to millers.

• The importance of protein content lies in the traditional belief that higher protein levels result in higher loaf volumes, therefore more profit for the bakers, because more loaves can be generated from a certain dough volume.

• Falling number indicates whether preharvest sprouting has occurred or not. Low falling numbers

(<220 s) indicates pre-harvest sprouting, which will result in “sticky” dough, leading to bread that is unacceptable to the baker as well as to his client, the consumer.

• Flour yield – the more flour obtainable from a given volume of wheat, the more profitable it will be for the miller.

• Flour colour – millers prefer wheat where bran-endosperm separation leads to a white flour in order to enable them to supply a constant product to their clients, the bakers.

• Peak time is determined by a Mixograph and it refers to the time that the flour takes to absorb water and to develop into an easy to handle dough. Short development times (<2 minutes) are undesirable for bread-making purposes, because it results in low loaf volumes, leading to a loss for bakers; although the opposite are also undesirable. Development times longer than 4 minutes, take too long, resulting in time and energy being wasted to develop the dough, therefore it again causes a loss for the baker.

• Water-absorption – higher water-absorption levels result in more dough per volume flour, therefore higher profits for bakers.

• Dough stability and elasticity are determined on an Alveograph. Low loaf volumes are obtained when dough is too stable, because it does not stretch easily. On the other hand, if dough stretches too much, it might tear during the fermentation process, gas might escape and low loaf volumes will also occur. A specific ratio between these two characteristics is of utmost importance.

• Loaf volume is the final test that a potential wheat breeding line has to pass before it can be released as a commercial cultivar.

Additional analyses that are performed for wheat breeders to assist with selections include:

• Thousand kernel mass, kernel hardness and kernel size as determined on a Single Kernel Characterisation System (SKCS).

• Gluten content – gluten, the unique protein in wheat, enables us to make dough which can stretch, rise and be baked to result in a loaf of bread.

• Kernel colour – wheat suitable for bread production usually exhibits a darker colour and higher protein content levels compared to wheat exhibiting a lighter (white) colour, which is usually utilised for biscuit production. Whiter wheat usually also tend to exhibit lower falling numbers.

• SDS-sedimentation volumes, refers to a sediment that forms after wheat flour has reacted with an acidic Sodium Dodecyl Sulphate solution and traditionally the belief is that the higher the sediment volume, the better the quality.

This laboratory was fortunate and is grateful for receiving funding from the Winter Cereal Trust to procure a computerised Mixograph as well as a Mixolab which will supply additional information to wheat breeders to enable them to select only the best that will be submitted for release as commercial cultivars.

The computerised Mixograph allows for determination of 44 data-points compared to earlier days, where only peak time could be measured manually on a Mixogram. Peak time is the only Mixogram parameter though that are considered during the release of commercial cultivars, but unfortunately, peak time has no relationship with loaf volume – the final test for bread wheat quality.

The Mixolab is the only equipment that gives information simultaneously on protein, starch and enzyme properties.

To ensure accuracy, this laboratory takes part in wheat and flour ring tests sent out monthly by Premier Foods (SASKO) and quarterly by the Southern African Grain Laboratory (SAGL) in Pretoria.