For the reference sample, |E| decreases with increasing temperature
up to 100 C, followed by a short temperature interval where
|E| levels off. This rubbery-like plateau extends from 100 up to
110 C. Finally, the flexural complex modulus starts increasing
again, evidencing an apparent thermosetting potential even after
compression-moulding. This outcome may most probably be the
result of a part of the wheat gluten protein yet to denature after
dough post-treatment at 90 C (Jerez et al., 2007a; Gonzalez-
Gutierrez et al., 2010). In fact, as previously shown, this viscoelastic
growth region becomes more apparent when the dough is processed
at temperature lower than 90 C or dampens and eventually
vanishes by processing at higher temperature (Zárate-Ramírez
et al., 2011). Formic acid addition also seems to exert a clear and
pronounced influence on broadening the temperature interval over
which the rubbery-like plateau extends, and consequently, on
decreasing the bioplastic temperature susceptibility. This plateau
region has been extensively described in polymer rheology in
terms of an entanglement network formed by the simple topological
interaction of polymer chains. It arises at frequencies higher
(timescale shorter) than the lifetime of the topological entanglements
(Ferry, 1980). However, for these protein-based systems, it
may be attributed to a situation that falls between a temporary
entangled network and covalent crosslinking (Ross-Murphy,
1995), as hydrophobic interactions usually act not at a point on
the chain as covalent crosslinks do, but involve more extended
‘‘junction zones’’. This effect becomes more important with
increasing acid content, as it may be increasing the number of sites
available for interactions among chains, probably by inhibiting
protein aggregation, as previously mentioned.