3.2. Dynamic mechanical analysis of a poultry protein during cooling
In the course of sample cooling from 78 C to 20 C the stiffness
modulus G1 in the control system was increasing monotonously
(Fig. 1). This may be connected with the reorganisation within
intermolecular bonds in the tested systems.
Upon cooling the cooked gel, hydrogen bonds reform, adding
stiffness to the system, and some of the a-helix structure reforms.
At the same time, the b-structure of the proteins is formed
between protein chains which were randomized upon heating.
Wang and Smith (1994b) showed that in myosin isolated from
chicken breast muscles, heated above 55 C and cooled to 25 C
hydrogen bonds were formed in b-structures of proteins. This contributes
to the stabilisation and increase in elasticity of the actomyosin
gel network and an increase in its elastic properties.
Cooling of MP systems containing microbial transglutaminase from
78 C to approx. 35 C leads to a linear reduction of G1 values. This
may be connected with a weakening of hydrophobic interactions
progressing with a decrease in temperature. This is suggested by
changes in elasticity of entropic character, typical of covalently
bound polymers (Case et al., 1992). Below 35 C, similarly as it is
the case in the control system, the spatial gel network is stabilised
by hydrogen bonds.
When the gel is prepared at high temperature (>60 C), rapid
unfolding of proteins results in more intense coagulation. The presence
of transglutaminase in the system enhances this effect. This
means that more water is released from the gel network (Niwa,
1992).