2018 Volume 46 Issue 1 Pages 1-12
Correlations between static rheological properties (G: shear modulus, μ: viscosity, μapp: apparent viscosity) of four food fluids (thickening agent solution, yoghurt, tomato puree and mayonnaise) measured employing a newly developed non-rotational concentric cylinder (NRCC) method and dynamic viscoelastic properties (|G*|: complex shear modulus, G′: storage shear modulus, G″: loss shear modulus, |η*|: complex viscosity, tanδ: loss tangent, μapph: apparent viscosity) measured by a conventional apparatus (HAAKE MARS III) were studied. μapp and μapph for each sample fluid agreed well. μapp≒|η*| obeying the Cox–Merz rule was obtained for the thickening agent solution, μapp < |η*| for mayonnaise and μapp << | η*| for tomato puree and yoghurt. μ was lower than μapp or μapph for all samples, and reached μapp with an increasing shear rate. Plotting G and |G*| against the shear rate and angular velocity respectively in the same figure revealed G < |G*| for tomato puree, G≒|G*| for yoghurt and G > |G*| for mayonnaise and thickening agent solution. The applicability of two-element models in analyzing the viscoelastic behavior of sample fluids was investigated by comparing two characteristic times τM = 1/(ωtanδ) and τK = tanδ/ω, corresponding to Maxwell and Kelvin–Voigt models respectively and evaluated from measurements of tanδ, with τ = µ/G and τapp = µapp /Gapp calculated from rheological properties measured by the NRCC method. Here Gapp (= G(μ/μapp) is an apparent shear modulus newly defined to evaluate the shear-rate dependency of the elasticity of Non-Newtonian fluids. Results show τK agreed well with τapp, suggesting the possibility of applying the Kelvin–Voigt model to the viscoelastic behavior of sample fluids.
