Chemistry Reference
In-Depth Information
twice and the texture dimensions, for example hardness, cohesiveness
and adhesiveness, could be calculated from the force response. This
approach is still extensively used. For example, it is one of the standard
software packages on commercial instruments for the measurement of
food texture. There have been early attempts to consider this approach in
more fundamental rheological terms, but in the authors' opinion, there
is little point in doing so. Texture profiling can be useful, but it is some
way from what most people would regard as rheology. A good discus-
sion of empirical measurements of food texture is given in the topic by
Bourne (2002), and elements of this are addressed in other chapters in
the current volume.
This contribution focuses on the relationship between perception and
fundamental rheological parameters. The work considered will be on
liquids or gels, since these are isotropic and homogenous and therefore
more amenable to a fundamental rheological approach. Of course, the
word homogenous needs to be associated with a distance scale, but
in this context, emulsions such as milk are considered homogenous,
whereas a meat chunk in gravy product is not.
The topics covered are as follows:
(i) Rheology and thickness perception.
(ii) Rheology and flavour perception.
(iii) Mixing, microstructure, mouthfeel and gels.
(iv) Beyond shear rheology.
Following guidance from the editors, this chapter will focus more on
(ii), (iii) and (iv), since there has been a considerable recent inter-
est in this area by the lead author and colleagues at the University of
Nottingham.
8.2
RHEOLOGY AND THICKNESS PERCEPTION
The relationship between the rheology of liquids and thickness percep-
tion should be the simplest to address experimentally. This is because at
first sight, the only relevant rheological parameter is an instrumentally
measured shear viscosity. Since most foods are non-Newtonian, i.e. vis-
cosity depends on shear rate/shear stress, it is necessary to decide what
the measurement conditions for the best correlation with sensory per-
ception are. The first study that was done to determine the appropriate
shear rate for the measurements of a viscosity which would correlate
to thickness perception was carried out by Wood (1968). This approach
involved using a sensory panel to compare the perceived thickness of
non-Newtonian liquid foods (cream soups) with Newtonian glucose
