Strain and strain rate dependence of gellan, agar and agar–gellan gels as model systems.

Gellan, agar and their combination gels (1:1, 2 g/100 g) as model systems were subjected to strains up to
0.8 while varying the crosshead speed between 0.01 and 10 mm s�1 to determine different textural
characteristics (Young’s modulus, rigidity constant, degree of concavity and apparent biaxial elongational
viscosity, gbe) and fracture characteristics. The compression curves usually consisted of 6 zones, and the
gels were sensitive to strain rate and the extent of applied strain. Agar gel showed higher fracture force
and energy compared to gellan and agar–gellan samples. However, the fracture strain for gellan was
highest (44.6–70.7%) followed by agar (22.8–40.3%) and agar–gellan (24.3–37.3%) gels indicating more
brittleness in agar/agar–gellan gels but toughness in gellan samples. The degree of concavity of gellan
gel was less than 1 indicating strain-softening characteristics; the agar gel exhibited strain-hardening
phenomenon as it was more than 1. However, marginal strain-softening behaviour was observed for
gellan–agar combination gel (0.856 6 n 6 0.999). A power law type model linked gbe and the biaxial
extensional rate at fracture. Gellan gels are suitable to prepare chewable fabricated juicy gels, while
brittle products resulted from agar/agar–gellan. It is proposed that gbe at fracture is a good index for characterising
gels in relation to product development and compression-spreading.