ORAL PERCEPTION OF VISCOSITY IN FLUID FOODS AND MODEL SYSTEMS

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Abstract
The perceived in‐mouth thickness (T) of a range of fluid foods and model systems was assessed by a trained sensory panel, using a ratio scaling technique, and correlated with objective measurements of viscosity (ηN). For Newtonian samples a simple linear correlation (r2= 0.98) is observed between log T and log η with exponent η= 0.22. The linear relationship between log T and log η for Newtonian materials was used to calculate the equivalent Newtonian viscosity (ηN) from subjective panel scores for the non‐Newtonian samples studied. The shear rate at which observed viscosity is equal to ηN decreases with ηN, as reported previously by Shama and Sherman, but also decreases with increasing shear‐rate dependence of viscosity. This implies oral perception of viscosity over a range of shear rates. Comparison of flow curves for samples assigned similar thickness scores, but showing very different shear thinning behaviour, suggests that the perceived thickness of extremely shear‐thinning materials is dominated by their high viscosity at low rates of shear. As a simple practical index, viscosity at 10 s−1 shows a better correlation (r2= 0.95) with the perceived thickness of the samples studied than values calculated by the methods suggested by Wood, or by Shama and Sherman (r2= 0.90 in both cases). The close agreement between panel scores for perceived thickness and perceived stickiness previously observed for concentrated solutions of random coil polysaccharides does not apply for several of the food systems studied, or for very concentrated solutions of xanthan.