Chemistry Reference
In-Depth Information
using the dentition. The threshold of hardness was 0.08 kg (force) for
the agar gel and 0.03 kg (force) for the gelatine gel.
Oral management of liquid food products is similar, but processing in
the mouth is not required, so typically only the preparatory and propul-
sive stages exist. Hiiemae and Palmer (1999) reported the relevant times
for both processes as being in the order of a few seconds. Again, one
of the difficulties in this area is the fact that literature seems to origi-
nate from the medical field and thus focuses on understanding clinical
conditions (Silva
et al
., 2008) and does not focus on understanding oral
behaviour of food structures and their changes during eating.
One of the difficulties in studying phenomena occurring
in vivo
is
related to the challenge and the limited number of experimental tech-
niques available. Videofluorographic studies have been used in the past
(Hiiemae and Palmer, 1999). Recent advances in medical imaging have
allowed the use of functional magnetic resonance imaging (fMRI) to
study phenomena during eating. Felton
et al
. (2007) studied tongue
movements and strain rates during swallowing of water. The authors
have found that swallowing requires a range of coordinated compres-
sive and expansive movements that last in the order of 500 ms. From
the obtained images, the strain rates experienced on the tongue have
been estimated and found to be both positive and negative with a mag-
nitude of about 0.2 per second. Developing fMRI techniques to study
phenomena occurring during eating is an active area of research, but
conclusive quantitative results have not been published yet (Barkhausen
et al
., 2002; Humbert and Robbins, 2007). A technique based on video
rate endoscopy has also been developed and used to investigate the in-
teractions between food material and oral surfaces, with an emphasis on
food residues remaining in the mouth after swallowing; for example, the
same study demonstrated that the material remaining onto the surfaces
in the mouth after swallowing increased exponentially with increasing
viscosity of the food (Watson
et al
., 2002; Adams
et al
., 2007; Pivk
et al
., 2008).
9.3.2
Fluid dynamics during oral processing
Behaviour of emulsions under application of forces has been an active
field of study (Windhab
et al
., 2005). During oral processing, large
shear and elongational forces are applied to the food materials. This
has a profound effect on the structure and has an effect on consumer
perception. As oral movements are not only complex but also variable,
obtaining a concise understanding of the flow fields and the forces and
deformation experienced from the food material is challenging to say
the least. Recently, effort has been devoted to estimate clearance times
and shear rates during oral processing (Nicosia and Robbins, 2001).
