Chemistry Reference
In-Depth Information
2.2
FOOD RHEOLOGY
Foods can be classified in different ways, such as solids, gels, homoge-
neous liquids, suspensions of solids in liquids and emulsions (Gallegos
and Franco, 1999; Fischer
et al.
, 2009). Foods that do not retain their
shape but take the shape of their container are fluids. Such materials
may contain amounts of dissolved or suspended solids, and exhibit
non-Newtonian behaviour (described in detail in the later parts of the
chapter), which classifies them as semi-fluids (Baird, 1981; Decindio,
1994). Many of these exhibit both viscous and elastic properties and
can be described as viscoelastic materials. In contrast, if fluids con-
tain dissolved low-molecular-weight compounds (e.g. sugars) and no
polymer or insoluble solids, they may show Newtonian behaviour (Rao,
1977). However, a small amount (
1%) of a dissolved polymer can
substantially increase the viscosity and alter material behaviour from
Newtonian to non-Newtonian (Blair, 1954).
Rheometry helps in understanding the responses of food structure
to applied forces or deformation and also provides information on the
dependence of food structure on overall composition and interaction
between the components (Shoemaker and Borwankar, 1992). Many ap-
proaches to rheometry are possible depending on what is expected from
the measurements; i.e. is it for prediction of flow behaviour of mate-
rial in a process or for characterising the material without damaging its
structure?
The classification of rheological behaviour and the measurement of
rheological properties of fluid foods have been reviewed by Blair (1954),
Muller Hans (1973), Baird (1981), Ross-Murphy (1984), Borwankar
(1992), Rao and Steffe (1992), Stanley and Taylor (1993), Decindio
(1994), Steffe (1996), Lareo
et al.
(1997), Mankad and Fryer (1997),
Rao (1977, 1999, Lareo and Fryer (1998), Kasapis
et al.
(2000) and
many others. Techniques for measuring rheological properties, espe-
cially flow properties, are covered by Van Wazer
et al
. (1963) and those
of viscoelastic properties by Whorlow (1980) and Macosko (1994). Rao
(1999) in his topic discussed in detail the rheological properties of fluid
and semi-fluid foods.
∼
2.3
DIRECTIONS OF RHEOLOGICAL RESEARCH
Ferguson and Kemblowski (1991) have described the focus in rhe-
ological research, in terms of four branches: (i) phenomenological
rheology, (ii) structural rheology, (iii) rheometry and (iv) applied
rheology.
