Effect of aging and drying on thermomechanical properties of white bread as characterized by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC).
Vodovotz Y. | Hallberg L. | Chinachoti P.
The effects of drying and storage on white bread was investigated using dynamic mechanical analysis (DMA), and the means for quantifying the results were explored. The "freezable" water content was obtained from differential scanning calorimetry (DSC) endotherm in ice melting region. A typical DMA thermogram of a high-moisture bread (>30%, w/w) resulted in a broad transition region, as evidenced by the tan delta curve and E' drop spanning a temperature range of 50 degrees C in the ice 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 decreased in height and broadened while the E' descending slope decreased. At <30% moisture, the tan delta curves were best fitted with a single Gaussian curve, while at >30% moisture, best fit was obtained with a Gaussian 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 bread. 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, overlapping 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 domains).
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