Dough rheology and wheat free asparagine content: Implications for bread quality and safety

Producing wheat of low free asparagine content is one strategy to meet international goals for allaying food safety concerns that arise from acrylamide formation in bread. However, factors that affect free asparagine in wheat also affect protein content and composition, and through their effects on dough viscoelasticity, bread quality. We investigated relationships between dough rheological properties and wheat free asparagine concentration using dynamic and static shear rheometry. From a population of 128 wheats, 10 were selected from which doughs with a wide range of asparagine concentrations were prepared. Within the linear viscoelastic region (LVR), dough's tanδ and free asparagine concentration were positively related, a result that appears to depend on protein composition. Outside the LVR, significant relationships between rheological parameters and free asparagine content were found. The dough's relative capacity to recover in creep-recovery tests was significantly impaired at elevated asparagine content. Similarly, stress relaxation tests showed that as wheat asparagine content increased, dough relaxation moduli decreased. Excellent fits of stress relaxation curves to a two-element Maxwell model were obtained. Both relaxation times decreased as asparagine concentration increased, showing that gluten strength attributes arising from gliadins and network-structuring proteins were both negatively affected in wheats of high asparagine content. In summary, wheat with high free asparagine concentrations led to more fluid-like doughs, i.e., weaker glutens. A welcome result is that strategies pursued to reduce acrylamide in bread through reduction in wheat's asparagine content will not impair bread quality.