Crop production: Which factors determine wheat quality?


By Digital team | 12 September 2018
wheat
Photo: Amelia Genis

Everyone, from the farmer to the baker, have their own ideas about what makes good wheat. Certain wheat qualities should, however, always be kept in mind.

It can take at least 10 years from when a wheat crossing is made until a cultivar is released to the industry. Wheat breeders may start with a thousand crossings, and after 10 years only 1 cultivar may be released to the industry.

The Wheat Technical Committee in South Africa, for instance, sets certain quality standards with which a cultivar has to comply before it can be released. These standards include that a potential breeding line should yield enough flour – the more flour the more profitable it will be for the millers.

A potential breeding line should also be able to absorb a certain quantity of water and to produce a certain loaf volume. Again, this is important to bakers.

Quality traits are controlled by several genes and they also take several years to settle in before a cultivar exhibits the required traits. It can take a long time to have enough seed to conduct tests needed to give the correct indications to millers and bakers. The environmental effect on production should also be remembered.

The following traits are important to farmers:

  • Hectoliter mass (test weight).
  • Falling number.
  • Protein content.

WHAT IS HECTOLITER MASS?

  • Hectoliter mass is an indication of wheat kernel density.
  • Denser kernels yield more flour making these more profitable for millers.
  • Kernel density indicates whether kernels are plump and well-filled or not.
  • Stress factors occurring during the plant’s grain-filling phase result in lower test weights.
  • These factors include drought, excessive soil moisture, a shortage of nutrients, too little sunlight, too low or too high temperatures, insect damage and weather damage such as frost and hail.
  • The reaction of wheat kernels to these environmental conditions can be genetically controlled.
  • Kernel shape, which can be genetically manipulated, also influences hectoliter mass.
  • Kernels that are rounder and have smaller grooves are preferable.

WHAT IS FALLING NUMBER AND WHY IS IT IMPORTANT?

  • Wheat flour consists mainly of protein and starch.
  • Starch plays the greatest role in bread structure.
  • If it rains on ripe wheat and favourable weather conditions follow, pre-harvest sprouting occurs.
  • When this happens, the starch is broken down by an enzyme, alpha-amylase, and excessive sugars form (referred to as low falling numbers).
  • Excessive sugars lead to “sticky”, runny dough that’s difficult to handle mechanically.
  • Bread has a dark crust, coarse texture, poor structure and cannot be cut by machine.

WHAT INFLUENCES FALLING NUMBER?

  • Environmental factors, such as wet weather and daily temperatures, have a profound effect on pre-harvest sprouting.
  • Wheat also tends to be more susceptible to pre-harvest sprouting during the kernel-hardening growth stage.
  • This trait is mainly determined genetically and breeding lines that exhibit no resistance to pre-harvest sprouting are discarded during the early breeding phases.
  • The environmental impact on this trait is large in South Africa, since only little genetic resistance to pre-harvest sprouting is available in this market.
  • The effect of normal wheat versus pre-harvest sprouted wheat on the end-product can be seen in the illustrations below.

WHAT IS PROTEIN CONTENT AND WHY IS IT IMPORTANT?

  • Protein content refers to the amount of protein in a wheat sample.
  • Wheat’s protein structures make it suitable for use in bread, pasta or biscuit production.
  • A direct relationship exists between the specific type (composition) of protein and end-product it should be able to produce.
  • In the case of wheat, this protein is called gluten.
  • Gluten can be divided into a glutenin fraction, (which confers stability on dough) and a gliadin fraction, (which gives elasticity).
  • A balance between these two fractions is important, because it determines end product quality.
  • Dough should be elastic so it can stretch during fermentation, and it should be strong enough not to tear while it stretches.
  • It should trap the gas and allow the dough to rise for an attractive end product.

WHAT INFLUENCES PROTEIN CONTENT?

  • Environmental factors such as fertiliser used, moisture availability, as well as the genetic background of a cultivar, can influence the balance between different protein fractions.
  • Different cultivars will exhibit different loaf volumes at the same protein content levels, because of their genetic background.
  • Nitrogen fertiliser leads to higher protein content.
  • Greater nitrogen availability means an increase in the gliadin fraction resulting in more elastic dough.
  • Moisture stress also increases protein content, because less starch is formed.
  • Usually, higher protein contents (within a normal range of 10% to 14%) will result in higher loaf volumes – more profitable for bakers.
  • It’s important to remember that protein quantity (content) as well as protein quality (composition) determine the success of the end product.
  • The 3 important characteristics to wheat farmers, clearly, are influenced by the environment as well as production practices.
  • The reaction to them is also influenced by their genetic make-up, and the genetic effect differs for each quality trait.
  • So the proportion that can be manipulated by breeding will also differ.

Also read:
An introduction to producing wheat
Better profits by understanding wheat

  • This article was written by Chrissie Miles and first appeared in Farming SA.