Chemistry Reference
In-Depth Information
the range of speeds that can be obtained is fairly limited. This means
that traditional Stribeck curves are not easy to obtain, and therefore,
only timed experiments at a fixed speed can be carried out.
In their study, Ranc
et al
. (2006) further investigated the lubrication
behaviour of emulsions undergoing time-dependent structural changes
and analysed the effect on perception. A range of emulsions were
studied, both
in vivo
and
in vitro
, with the obtained results suggesting
that those more prone to coalescence were perceived as more fatty and
had reduced friction (Dresselhuis
et al
., 2008b). This can be explained
by the fact that coalescence increases the size of the emulsion droplets,
which makes them adhere and spread more easily on the tribometer
surfaces, thus leading to a lower friction value. In reality, this happens
only at low speeds, since above a certain (high) critical speed, emulsion
droplets are re-emulsified, and therefore, measured friction is increased
as they are expelled from between the surfaces. The modified tribometer
set-up, used by Ranc
et al
. (2006), was also adopted in a recent study
by Chojnicka (2009), where the frictional and sensory properties
of milk of varying fat content were investigated. Correlations with
multiple attributes, including perceived creaminess, were obtained for
fat contents between 1 and 4%, systems that also exhibited a reduced
friction at low speeds, within the mixed and boundary regimes. The
observed friction reduction was again attributed to coalescence events
between the oil droplets during measurement. Individuals were able
to distinguish between samples of different levels of fat, but this is
probably due to the differences in the viscosities between the samples.
What further supports this argument is the fact that the perceived
differences between the samples correlated with the differences in their
viscosities (Chojnicka, 2009).
9.5
FUTURE PERSPECTIVES
Design, processing and properties of emulsions have been extensively
investigated over the years. In the area of foods, proteins have been
commonly used to stabilise emulsions, and as such there is an interest in
trying to understand the ways proteins stabilise emulsion systems and
the properties they impart on them. Currently, there is a need to design
functional food products and more specifically lower fat alternatives
without compromising sensory properties. This has created a strong
interest towards understanding the ways that emulsion systems behave
under oral processing and the resulting sensory attributes.
Obtaining an understanding of oral processes and the changes these
induce to emulsion structures is an active area of research, but a signifi-
cant amount of work is still required to allow for the design of functional
