Effect of whole quinoa flour substitution on the texture and in vitro starch digestibility of wheat bread

Wheat breads are popular staples, while the ones with desirable textural attributes frequently have a high glycemic index value. The inclusion of different amount of whole quinoa flour (WQF) in wheat breads was investigated in this study, aiming to develop nutritionally fortified breads with both slower starch digestibility and desirable textural attributes. Results showed that although addition of WQF decreased the specific volume of wheat breads by affecting gluten network of dough, hardness and chewiness (the most important attributes affecting consumer acceptability) of those wheat breads were not significantly affected with an ≤ 20% of WQF substitution. On the other hand, addition of quinoa flour affected starch digestibility of breads. A 17% reduction of maximum starch digestion amount was reached by the addition of 40% WQF compared to wheat breads. By fitting starch digestograms to logarithm of slope (LOS) and combination of parallel and sequential (CPS) first-order kinetics model, it showed that two starch digestible fractions with distinct rate constants were existed in the bread system. Scanning electron microscope results showed that A type wheat starch granules were largely gelatinized, while B type wheat starch and quinoa starch granules were relatively intact and wrapped in the protein-sugar-oil film after baking. It could rationalize the occurrence of two different starch digestible fractions. This study suggests that increasing the ratio of B to A type wheat starch or addition of quinoa starch granules has potential to develop breads with both low glycemic index values and desirable textural attributes.