Chemistry Reference
In-Depth Information
G
"
G
'
Freqency (Hz)
Fig. 2.6
A typical graph of viscoelastic modules and their frequency dependency.
2.6
PROCESS, RHEOLOGY AND MICROSTRUCTURAL
INTERACTIONS
The microstructure of complex food products is greatly influenced by
the type of processing employed, and in particular the shear processes
and thermal processes, such as freezing. However, the effects are not
always well understood or easily quantifiable. As food processing oper-
ations are usually designed to create a microstructure that gives the food
product its characteristic properties, understanding of the microstructure
and the route to its formation is imperative (Aguilera and Stanley, 1999;
Aguilera, 2000). In rheometry also, the manner in which the material
interacts with the testing instrument varies according to the flow config-
uration used. This can lead to different microstructural rearrangements
that may result in different rheological responses. Therefore, a funda-
mental understanding of the relationship between processing, rheology
and microstructure is important for the control of product quality and
rheology (Guell and Papathanasiou, 1997). However, most of the work
on the effects of processing on food materials has been limited to inves-
tigations of flow behaviour, without consideration of the accompanying
structural changes (Cheyne
et al
., 2001).
2.7
RHEOLOGY OF SOFT SOLIDS
Concentrated pastes are used in a variety of industrial applications, such
as ceramic manufacture, as well as food processing. In food manufac-
ture, the 'ideal paste' is one that will undergo sufficient plastic or viscous
flow, so that it can be formed, and yet be rigid enough to retain its shape
during subsequent processing and handling. Therefore, food pastes are
generally complex heterogeneous materials with microstructure that
