Effect of viscoelasticity on foam development in zein-starch dough

- Zein-starch dough is a shear and extension thinning material.
- Strong correlation between shear and extensional viscosity, Trouton ratio of ≈30.
- Crumb structure development was unaffected by strain hardening.
- Bubble growth rate occurred upon steam formation during baking.
- The bubble wall extension rate at 140 °C was 0.05-0.1 s−1.

Above the zein glass transition temperature (∼40 °C), the viscoelasticity of zein-starch dough is similar to that of gluten. This is of interest because this dough might be used to develop gluten-free products, although it has certain limitations such as workability and aging at room temperature. The most effective way to decrease the dough glass transition temperature is to use a plasticizer, which also influences the viscosity. In this study, viscoelastic zein-starch dough samples were prepared with several concentrations of citric acid as the plasticizer, and the effect of viscoelasticity on crumb structure formation during baking was investigated. Extensional viscosity was correlated with the average bubble size after baking. We found that viscosity could be predicted for this system by measuring the shear viscosity, whereby the Trouton ratio was near-constant for the range of plasticizer concentrations investigated. In addition, our dynamic mechanical analysis (DMA) revealed that bubble growth occurs mainly when the dough reaches 100 °C, due to a combination of steam formation and thermal softening of the matrix. At higher temperatures, hardening occurs due to drying and zein crosslinking.