Tribology as a Tool to Study Emulsion Behaviour in the Mouth - Food Colloids: Self-Assembly and Material Science - page 460

opposite relation between particle size, friction force, and creaminess in their
custard systems as compared with our results. However, a system in which
emulsion droplets are entrapped in a gelled matrix is likely to behave differently
from one having a non-gelled continuous phase. Furthermore, de Wijk and
Prinz used artificial surfaces in their shearing experiments, and we have already
established that such surfaces differ greatly from the pig's tongue surfaces used
in our experiments.
From our combined friction data and sensory data, we conclude that the
presence of solid fat instead of sunflower oil in emulsion droplets enhances the
perception of creaminess, and that larger droplets give a more creamy sensation
and a lower friction force upon shearing.
31.6 Summary
There is a great interest in gaining more knowledge on the relation between
fat-related attributes such as creaminess and food emulsion properties. Var-
ious characteristics such as viscosity, release of fat flavour, and tribological
behaviour are suggested to be relevant for perception. In this study we have
focused on studying the ability of tribology to be a tool in understanding
emulsion in-mouth behaviour and consequently in understanding the percep-
tion of an emulsion. Tribological results are to a large extent determined by the
properties of the sliding surfaces. It is therefore crucial to use surfaces with
relevant properties. To mimic human oral surfaces we have used pig's tongues,
which we characterized in terms of roughness, wetting properties, and de-
formability. The effects of these surface characteristics on emulsion behaviour
were identified by comparison to an artificial surface (PDMS). Large differ-
ences in friction forces and coalescence behaviour were observed between
measurements conducted with pig's tongue and PDMS. Sensorial analyses
confirmed that a difference in the sensitivity of an emulsion to coalescence
indeed influences the fat perception of fat-related attributes. Furthermore,
emulsions more sensitive to coalescence also gave rise to a lower friction force,
indicating that tribology can be one of the tools in understanding emulsion
perception provided that mouth-relevant surfaces are used. Nevertheless, the
measured differences in friction force between the samples are small, suggest-
ing that tribology data should be supported by other confirmatory methods in
order to be a useful tool.
Acknowledgements
The authors thank Franklin Zoet and Jan Klok for their help in, respectively,
preparing the samples for the sensory tests and performing the OTC measure-
ments. We thank Monique Vingerhoeds and Rene de Wijk for analysing the
sensory data.