Chemistry Reference
In-Depth Information
threshold. In this very dilute region, non-Newtonian behaviour would
result from orientation of rod-shaped molecules rather than disruption
of entanglements.
8.4.4
Gels
Flavour perception from gels has been extensively investigated. The
majority of investigations have focused on individual or at most on
pairs of gelling systems. There is some analogy to work that has been
carried out on hydrocolloid-thickened solutions. Undoubtedly, there are
situations where binding of volatiles to the matrix will be significant in
reducing the levels of perception; however, it is particularly valuable to
develop a hypothesis that is applicable to as wide a range of textures and
gelling agents as possible. Many of the gel rheology studies have been
concerned with the small deformations required to remain within the
linear viscoelastic region. These parameters are less central to perception
than large deformation measurements which fracture gels. For example,
in a very early work, Wood (1979) showed that the perceived hardness of
a gel correlated better to the force required to facture the gel than to the
Bloom Strength which correlates with the small deformation modulus.
The study of Morris (1994) including a wide range of hydrocolloid
gelling systems showed stronger correlations between the strain at break
and perceived flavour as well as sweetness than that was seen for the
elastic modulus or the rupture stress. As with thickened solutions, one
question to be asked is whether this relationship can be understood in
terms of a change in the concentration of volatiles reaching the nose, the
concentration of tastants reaching the receptors in the mouth or whether
it is the result of a multimodal effect? It is reasonable that gels with
a lower strain at break (brittle gels) will release tastants and volatiles
more efficiently because of the more rapid increase in surface area on
consumption. In support of this, Morris demonstrated a strong negative
correlation between the strain at break and flavour perception for a range
of gels (Morris, 1994). A more recent study by Koliandris
et al
. (2008)
demonstrates that the increase in tastant release is a more significant
consequence of in-mouth processing of gellan and carrageenan gels
than the increase in volatile release.
It is generally accepted that gelatin is one of the best if not the best
gelling agent for taste perception and mouthfeel. In the authors' view,
there are two reasons for this:
30
◦
C which results in a gelatin gel
(i) A gel melting temperature
∼
melting in the mouth.
(ii) The efficient mixing of molten gelatin with water or saliva.
