Use of Dynamic Mechanical Thermal Analysis (DMTA): Glass transitions of a cracker and its dough

A Mark III DMTA (Polymer Laboratories, Loughborough, U.K.) was used to measure the glass transition temperatures (T_g) of a commercial cracker and its dough, each equilibrated to various water activities covering a range of 0.11-0.75 for the cracker and 0.11-0.90 for the cracker dough. DMTA measures the change in the elastic modulus (E′) and loss modulus (E″), as well as that in tanδ (E″/E′), with temperature. The change in the elastic modulus with temperature for the two systems followed a pattern similar to that found for complex food polymers (gluten, amylopectin), with T_g decreasing as moisture content increased. Baking did not change the location of the glass transition curve (T_g vs. moisture content); i.e. the curves for raw dough and baked finished product were somewhat superimposable, and similar to the published gluten curve, indicating that for this type of cracker containing ∼5% sugars, the protein fraction is most responsible for the T_g curve.