Use of dynamic mechanical thermal analysis (DMTA)

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), withT _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 theT _g curve.