The impact of the soluble protein fraction and kernel hardness on wheat flour starch digestibility

Wheat is the staple crop for 35% of the world’s population, providing a major source of calories for much of the world’s population. Starch is the main source of energy in wheat flour, but the digestibility of wheat starch varies greatly between different flours and wheat products. This has relevance from a health perspective because wheat starch products that are rapidly digested and elicit large post-prandial glucose peaks are associated with a host of cardiac and metabolic disorders. In this study, we investigate the impact of protein on starch digestion in three commercially sourced flours with different grain hardness. Grain hardness impacted on flour particle size, but not significantly on starch digestion. A soluble extract of wheat proteins was found to dramatically reduce starch digestion, even following gastric proteolysis. Proteomic analysis revealed that this soluble extract was enriched in proteinaceous α-amylase inhibitors which were partially degraded during gastric proteolysis. Therefore, we conclude that the soluble proteins of wheat flour have a significant contribution towards retarding starch digestion, even following gastric digestion.