  We investigated mixed-protein gels made from sodium caseinate and ovalbumin
at different ratios with use of the acidification agent
glucono-$\delta$-lactone. Dynamic viscoelastic measurements revealed that
increasing the ovalbumin content decreased the mechanical properties of the gel
but accelerated onset time of the phase transition. Ultrasound spectroscopy
during gelation revealed that the relative velocity gradually decreased,
whereas the ultrasonic attenuation increased during the whole acidification
process until gelation was complete, although these changes were much smaller
than those observed with heat-induced gelation. Confocal laser scanning
microscopy along with scanning electron microscopy revealed that although
uniform mixing of sodium caseinate and ovalbumin was observed, sodium caseinate
is likely to mainly lead formation of the gel network, and the porosity of the
resulting gel network depends on the ratio of these two components. The results
demonstrate that confocal laser scanning microscopy is a useful tool for
analyzing both the networks within mixed-protein gels and the contribution of
each protein to the network and gelation.
