Cereal Chem. 73 (2):264-270 |
Analytical Techniques and Instrumentation
Effect of Aging and Drying on Thermomechanical Properties of White Bread as Characterized by Dynamic Mechanical Analysis (DMA) and Differential Scanning Calorimetry (DSC).
Y. Vodovotz, L. Hallberg, and P. Chinachoti (1). (1) Food Science Department, University of Massachusetts, Amherst, MA 01003. Corresponding author. Fax: 413/545-1262. Accepted November 27, 1995. Copyright 1996 by the American Association of Cereal Chemists, Inc.
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 d curve and E(prime) drop spanning a temperature range of 50°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 d curve decreased in height and broadened while the E(prime) descending slope decreased. At <30% moisture, the tan d 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 d 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 d distribution (70 to 100°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°C) transition (although each of these major thermal events could arise from a distribution of multiple domains).