Starch discovery reaps benefits for industry

UK researchers have brought clarity to the longstanding question of how starch granules form in the seeds of Triticeae crops — wheat, barley and rye — unlocking diverse potential benefits for numerous industries and for human health. Their work has been published in the journal The Plant Cell.

Starch in wheat, maize, rice and potatoes is a vital energy-giving part of our diet and a key ingredient in many industrial applications, from brewing and baking to the production of paper, glue, textiles and construction materials. Starch granules of different crops vary greatly in size and shape, with wheat starch (and those of other Triticeae) having two distinct types of granules: large A-type granules and smaller B-type granules.

Unfortunately, the ratio of A- and B-type granules can affect the quality of wheat-based foods, such as bread and pasta. The two types of granules also present a problem for the starch manufacturing industry, as many of the smaller B-type granules are lost and therefore wasted during the milling process. Furthermore, too many B-type starch granules in barley can cause a hazy or cloudy appearance in beer because they do not get digested and filtered out during the brewing process.

Researchers at the John Innes Centre have now used genomic and experimental techniques to show that A- and B-type granules are formed by two distinct mechanisms. By identifying an enzyme involved in B-type granule initiation, PHS1, and by then using conventional plant breeding techniques to remove this protein, they were able to produce wheat with low or no B-granules — with no penalties on plant development and without reducing the overall starch content.

“This is a scientific breakthrough because decades of research on this enzyme have failed to find a clear role for PHS1 in plants, and it shows that the A- and B-type granules of wheat form via different biochemical mechanisms,” said Dr Nitin Uttam Kamble, first author of the study. “We can now use this knowledge to create variations in starch for different food and industrial applications.”

Industry has attempted many times over the years to solve the problem of mixtures of the large A-type and small B-type granules, including using multiple filtrations to catch granules lost during processing. Removing the requirement for these processing steps will reduce costs and improve product performance.

“Industry does not generally like heterogeneity; it wants something nice and even to process smoothly and having these different types of starch granules in wheat has always represented a challenge,” said Dr David Seung, a group leader at the John Innes Centre.

“So, for us to discover the enzyme responsible for making the smaller granule population and to be able to use our breeding platform to reduce the number of B-type granules will hopefully be of great interest to many industry users.

“Combined together with our previous work, we now have a panel of diverse, novel wheat starches that vary in granule morphology, and these have diverse physical and chemical properties. We now invite businesses to work with us to investigate the potential benefits of these starches, such as in milling, pasta- and bread-making.”

Starch used in industry is often modified using physical and chemical methods to achieve the specific properties required for each end use, so having ways to modify starch in plants may avoid these costly and often environmentally unfriendly modification processes. In addition to industrial benefits, the clarity about how starch granules are differentially initiated will open doors to greater understanding about the role that starch has in human diet and health — with future lines of enquiry to include how granule size affects starch digestibility, cooking quality, nutritional value and impact of dietary starches on human health.

The technology used in this research is available for evaluation and licensing through PBL Technology.

Image caption: Wheat starch granules observed under the scanning electron microscope; large A-type and small B-type granules are visible. Image credit: Brendan Fahy/Nitin Uttam Kamble.