International Journal of Biological Macromolecules
21 (1997) 231–241
Thermodynamic behaviour of gliadins mixture and the
glass-softening transition of its dried state
C. Ferrari, G.P. Johari *
Department of Materials Science and Engineering, McMaster Uni6ersity, Hamilton, Ontario L
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, Canada
Received 1 February 1997; accepted 22 April 1997
Abstract
The glass-softening transition of a mixture of gliadins extracted from wheat flour has been studied in its dry state
by differential scanning calorimetry (DSC). Further, the rate of removal of its water vapours on its evaporation from
a gliadins mixture containing different amounts of water has been investigated, and through this the presence of any
exothermic effect that could be attributed to polymerization of gliadins has been examined. The heat absorbed in this
evaporation is comparable with the heat of evaporation of pure water measured in a separate experiment in identical
conditions. This showed that the gliadins mixture did not polymerize on heating up to 473 K in the presence of
moisture. In this respect the behaviour of the gliadins mixture differs remarkably from that of gluten studied before
(J Phys Chem 1996:100:19692). The effects of purge gas, helium and argon, on the calorimetric effects during the
evaporation of water have been studied. A restudy of gluten shows that helium decreases substantially the
endothermic signal in the DSC measurements, and thereby reveals the exothermic effects of polymerization in gluten,
but argon does not do so. The structural relaxation time, t, of dry gliadins mixtures at different temperatures has been
calculated from an analysis of its glass-softening endotherm. The temperature at which t= 1 ks is 452 K, and the T
g
,
obtained by the usual method of intersection of the straight lines drawn, is 443 K, 7 K higher than for the
polymerized dry gluten, the distribution of relaxation time parameter is 0.25, and increase in the heat capacity in this
range is 0.21 J/g K. Physical ageing effects are considerable in the gliadins mixture, which alters the glass-softening
endotherm but not the structural relaxation time, or its distribution. © 1997 Elsevier Science B.V.
Keywords
:
Glass-softening; Gliadins; Differential scanning calorimetry
1. Introduction
The molecular dynamics of vegetable proteins
such as gliadins, [1] and gluten [2–4] differs sig-
nificantly from that of animal proteins such as
* Corresponding author. Tel.: +1 416 5259140; fax +1 416
5289295.
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