Osmotic Properties of Gluten

A model for dough is proposed in which the distribution of water between hydrated gluten and starch paste explains a number of practical observations such as 1) the extreme sensitivity of the consistency of dough to the amount of water in the recipe, and 2) the fact that working of the material results in an increase in consistency. The model assumes dough to be a composite material consisting of a starch paste and gluten filaments. During kneading, the starch granule paste in dough dries to become a phase with a yield stress as a result of the uptake of water by the stretching gluten filaments. This study focused on one particular aspect of this model: the osmotic properties of gluten during stretching. The results suggest that gluten can be hydrated more efficiently in the stretched state than in an unstretched conformation. Gluten hydration tends to change slowly over a period of weeks, which is accompanied by water expulsion or uptake, depending on the osmotic properties of the solvent. The rate of change does not seem to depend very much on pH and osmotic pressure for the current experimental conditions. The level of hydration of relaxed gluten depends strongly on pH, as expected. The experiments allow the construction of an osmotic pressure versus gluten concentration diagram over the range 4.6 < pH < 5.8. The level of hydration of the gluten is consistent with the proposed model for dough.