EFFECT OF AGING AND DRYING ON THERMOMECHANICAL PROPERTIES OF WHITE BREAD AS CHARACTERIZED BY DYNAMIC-MECHANICAL ANALYSIS (DMA) AND DIFFERENTIAL SCANNING CALORIMETRY (DSC)

The effects of drying and storage on white bread was investigated usin g dynamic mechanical analysis (DMA), and the means for quantifying the results were explored. The ''freezable'' water content was obtained f rom differential scanning calorimetry (DSC) endotherm in ice melting r egion. A typical DMA thermogram of a high-moisture bread (>30%, w/w) r esulted in a broad transition region, as evidenced by the tan delta cu rve and E' drop spanning a temperature range of 50 degrees C in the ic e melting region. DSC results show that freezable water was present at >33% moisture. With lower moisture, the observed transition appeared to move to a higher temperature range, and the tan delta curve decreas ed in height and broadened while the E' descending slope decreased. At <30% moisture, the tan delta curves were best fitted with a single Ga ussian curve, while at >30% moisture, best fit was obtained with a Gau ssian overlapping with an asymmetric sigmoidal curve. Some broadening of the tan delta peak was observed in staled bread (seven months), but the temperature, in general, remained in the same range as fresh brea d. The results also indicated that only extensive staling of bread (19 months) lead to a broad tan delta distribution (-70 to 100 degrees C) of transitions which could be deconvoluted into at least two major, o verlapping curves; while drying out of a fresh bread would only result in one major (-25 to 25 degrees C) transition (although each of these major thermal events could arise from a distribution of multiple doma ins).