Genetic and Agronomic Control of Free Asparagine Accumulation in Wheat (Triticum aestivum)

Acrylamide is a processing contaminant found in many different foods. It is formed from free (soluble, non-protein) asparagine and reducing sugars during the Maillard reaction, which occurs during low-moisture, high-temperature processing. In wheat-based food products, free asparagine is the key determinant of how much acrylamide forms, so the amount of acrylamide in wheat-based food products can be decreased by minimising the amount of free asparagine that accumulates in wheat grain. Agronomic and genetic strategies have previously been explored to reduce free asparagine accumulation in wheat grain, but a small proportion of products still continue to exceed recommendations set by the European Union, likely due to fluctuations in free asparagine content. Consequently, there is a need to develop more strategies to limit free asparagine accumulation in wheat grain.
In this thesis, new findings relevant to the genetic and agronomic control of grain asparagine accumulation are discussed. Firstly, a presence/absence variation of one of the asparagine synthetase 2 homoeologs was analysed and found to reduce grain free asparagine content in the field. Secondly, variation in grain asparagine content and other traits was explored in a soft wheat mapping population, enabling identification of a QTL controlling free asparagine. A soft wheat population was used because this project sought to reduce the acrylamide content of soft wheat products, most notably biscuits. Finally, the impact of different fertilisers on grain asparagine accumulation was investigated in the field, facilitating further analysis of how this translates to differences in biscuit acrylamide content and the potential for imaging of plants and seeds to predict grain asparagine content. This showed that a nitrogen to sulphur application ratio of 10:1 (kg/ha) was sufficient to prevent large increases in free asparagine and that imaging could accurately predict free asparagine content. Overall, this body of work highlights interesting effects of genetic and environmental factors on grain asparagine content that can be used to inform future strategies for grain asparagine reduction.