Effect of storage time and temperature on rheological and microstructural properties of gluten

To investigate the effects of frozen storage on the rheological and microstructural properties of gluten, two model systems were investigated: System A, gluten and water; System B, gluten, water, and NaCl. The storage time was varied from 1 to 16 weeks and the storage temperature was varied from -5 to -30 degrees C. After thawing, uniaxial and biaxial deformations, and stress relaxation measurements were performed on gluten. In System A, the major effects were noticed when the gluten was stored at -5 degrees C. Frozen storage induced a decrease in stress and in strain at breaking, but an increase in modulus (stress/strain) under uniaxial deformation. In System B, only stress relaxation measurements showed differences between the fresh gluten and the gluten stored at -18 degrees C. These results suggest that at -5 degrees C, gluten strands form more entanglements. Microscopic analyses of frozen gluten showed that, during the freezing step, ice crystals compressed the gluten. A significant phase separation was observed between gluten and ice but no difference was observed between the storage time and storage temperature. However, after thawing, gluten microstructure exhibited a structure similar to the fresh gluten, and the structure looks like a sponge (a fine gluten structure with tiny water pockets).