Differential scanning calorimetry glass transition temperatures of white bread and mold growth in the putative glassy state

Differential scanning calorimetry (DSC) was used to determine the onset and end temperatures of the glass transition (T(g)) for white bread equilibrated between 53 and 84% rh. Calorimetric T(g) end values were approximate to 20 degrees C higher than onset values, indicating that it is probably more correct to refer to a "glass transition range" rather than a glass transition temperature. Slices of white bread inoculated with a mixture of xerophilic molds were equilibrated to 75% rh (equilibrium moisture content of 14.5 g of water/100 g of dry material) and stored at 26 degrees C. In a parallel experiment, some of the equilibrated bread samples were stored without mold inoculation and subjected to spontaneous contamination from the immediate surroundings. As suggested by measured T(g), bread stored at 75% rh and 26 degrees C appeared to be glassy. After storage, samples of bread (inoculated or not) were spoiled by xerophilic molds, suggesting that T(g), as measured by DSC, cannot be considered as an absolute threshold for mold growth inhibition.