Abstract
Gellan, agar and their combination gels (1:1, 2g/100g) as model systems were subjected to strains up to 0.8 while varying the crosshead speed between 0.01 and 10mms−1 to determine different textural characteristics (Young’s modulus, rigidity constant, degree of concavity and apparent biaxial elongational viscosity, ηbe) 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⩽n⩽0.999). A power law type model linked ηbe 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 ηbe at fracture is a good index for characterising gels in relation to product development and compression-spreading.
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