Jozef L. Kokini

The physical basis of liquid food texture and texture-taste interactions☆

Abstract This paper reviews recent efforts, mostly at the authors laboratory, to relate liquid and semi-solid texture to rheological and frictional properties and to relate texture-taste interactions to diffusion coefficients. First, the large texture vocabulary is reduced to a few key attributes of ‘thick’, ‘smooth’ and ‘slippery’ using statistical analysis. A model is presented approximating the deformation process and capable of predicting shear stress in the mouth, which is solved for Newtonian, ‘non-Newtonian’ and ‘non-Newtonian foods with time dependent rheology’. Shear stress is then related to magnitude estimation of ‘thickness’. Similar approaches lead to prediction of ‘spreadability’ using a knife. ‘Smoothness’ is shown to be related to the inverse of the friction force required to have skin slip across skin or food, and ‘slipperiness’ is shown to be related to the inverse of the sum of viscous and frictional forces. ‘Creaminess’ is shown to be predicted from scores of ‘thickness’ and ‘smoothness’. Viscosity-taste interactions are explained by assuming that the rate of diffusion of tasting agent to the surface of the tongue is slower than the rate of the taste reaction responsible for the intensity of a tasting reaction. Therefore, the ‘flux’ of tasting agent controls the rate of the tasting reaction. The penetration model of mass transfer suggests that this flux is proportional to the square root of the diffusion coefficient. This concept is shown to explain viscosity-taste interactions.

Wall effects in the laminar pipe flow of four semi-solid foods

The objective of this study was to estimate the contribution of the apparent slip phenomenon to the capillary flow of ketchup, mustard, apple sauce and tomato paste. QπR3τw calculated at constant wall shear stress was plotted against IR2. The linearity of these plots suggested that corrected slip coefficients βc could be calculated from the slopes of the resulting lines at specific values of τw. Slip velocities could also be calculated as a function of wall shear stress and it was found that a power function of slip velocities could be related to wall shear stress. Omission of slip corrections in rheological measurements of these materials could result in errors of up to 70–80% in their shear rate component.

Steady shear viscosity first normal stress difference and recoverable strain in carboxymethyl cellulose, sodium alginate and guar gum

Abstract Steady shear viscosity, first normal stress difference and recoverable strain in carboxymethyl cellulose, sodium alginate and guar gum were studied. A master curve was obtained for the viscosity of sodium alginate and guar gum. The data for sodium carboxymethyl cellulose deviated from that of guar gum and sodium alginate. Superposition principles for the normal stress coefficient with a reduced shear rate have been attempted. Superposition was obtained for all three hydrocolloids. Additionally, the first normal stress difference appeared to be highly related to shear stress for sodium alginate and carboxymethyl cellulose at all concentrations studied. Guar gum did not follow this behavior.