Comparison of texture analyser and rheometer measurements on carrageenan and pectin gels

ABSTRACT The viscoelastic behaviour of a number of carrageenan and pectin gels was measured in three ways: a- The so-called ‘texture analysis’ consisting of stress-strain measurements on a gel confined in a stiff cylindrical dish and having a diameter larger than the probing plunger; b- Parallel plates compression stress-relaxation; c- Parallel plates oscillatory torsion shear deformation. The main scope of the study was to find a correlation between the routine quality control measurement (a) and the material properties [complex moduli (c)]. The results presented here address the low deformation limit of texture analysis, whereby an apparent compression modulus can be calculated. Depending on the diameter of the plunger and the height and diameter of the sample, the values found were up to 15 times higher than the true Young's modulus. Qualitatively this finding is related to the contribution to the stress of the sample deformed outside the plunger's cross-section, the lateral confinement of the sample, combined with the incompressibility of the gel. The experimental data were compared with boundary element calculations from ref.1. The model calculations described the experimental data quantitatively, except for the thinnest samples.