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Differential Scanning Calorimetry Glass Transition Temperatures of White Bread and Mold Growth in the Putative Glassy State

¹Departamento de Industrias, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, (1428) Buenos Aires, Argentina. ²Member of CONICET, Argentina. ³Department of Food Technology, PO Box 27 (Latokartanonkaari 7), FIN-00014 University of Helsinki, Helsinki, Finland. ⁴Corresponding author. E-mail: jchirife@tealim.fcen.uba.ar

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 ≈20°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°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°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.