Structure of Self-Assembled Globular Proteins - Food Colloids: Self-Assembly and Material Science - page 51

Figure 14 CLSM images of mixtures of k -carrageenan (10 g L 1 ) with b -LG aggre-
gates: (a) 0.2 g L 1 b -LG; and (b) 10 g L 1 b -LG 58
shows I p q 4 , which implies that the micro-domains are homogeneous and
have a well-defined interface. Initially, the aggregates in the micro-domains are
only loosely bound and can be dispersed by dilution so that the original
aggregates are recovered. However, the domains transform into irreversibly
bound micro-gels over a period of a day or two. Interestingly, smaller aggre-
gates exit the liquid domains when the polysaccharide phase is gelled, 60 indi-
cating less incompatibility of the aggregates with gelled polysaccharide. The
structure of the agglomerated micro-domains formed by mixing pre-heated
protein aggregates and polysaccharide at room temperature resembles that of
the gels formed by heating mixtures of native protein and polysaccharide.
Confocal microscopy shows that the structure of these mixed gels is similar
to that of heterogeneous gels formed by pure globular proteins in the presence
of high salt concentrations or close to pI. 56,61,62 However, no micro-phase
separation of protein aggregates is observed when salt is added to the solutions
or the pH is lowered. Instead, a slow 'cold gelation' process is observed. 10 The
structure of large clusters formed by the association of small aggregates at
room temperature is similar to that of large clusters formed by heating native
proteins. Interestingly, gels at high salt or close to pI are generally more
homogeneous when they are formed from clusters made by pre-heating at
conditions of low salt and far from pI than when they are formed by directly
heating native protein. 55,63,64 This would suggest that micro-phase separation
does not occur during the formation of pure globular protein gels.
3.4 Relationship between Structure and Linear
Elasticity
One approach to calculate the shear modulus of globular protein gels is based
on the hypothesis that the shear modulus is proportional to the concentration