mechanical test results, but probably in a different manner. If the
food is strongly anisotropic, as is the case with most kinds of meat,
additional uncertainties arise.
The conditions during the test should also in other respects be similar
to those in the mouth.Temperaturecan be readily adjusted, but the
dilution withsaliva, or its lubricating effect, may be more difficult to
mimic.
17.2 GELS
Apart from a discussion of functional properties, this section will be divided
according to the network structure of gels. Flory* gave the following
structural classification:
- Well-ordered lamellar structures, including gel mesophases
- Covalent polymeric networks; completely disordered
- Polymer networks formed through physical aggregation; predo-
minantly disordered, but with regions of local order
- Particulate disordered structures
Types 2–4 are illustrated in Figure 17.10, frames (a), (b), and (c),
respectively.
We will here only consider types 3 and 4—calledpolymer gelsand
particle gels, respectively—which are both common in foods. Type 1 can
occasionally occur in foods, but the concentrations of small-molecule
surfactants needed to obtain such gels are generally too high to be
acceptable. Type 2 does not occur, although some covalent bonds between
structural elements occasionally contribute to gel structure, such as
22 S 22 S 22 bridges between protein molecules. Several intermediate gel types
occur in foods, and some of these will be discussed.
17.2.1 Functional Properties of Gels
Food gels are made for a specific purpose, which generally means that the
gel should have one or more specific physical properties. When making a
pudding, for instance, it is desirable that it should not sag under its own
weight during keeping, a property often called ‘‘stand-up.’’ Neither should
the pudding fracture, e.g., fall into pieces during transport. Another stability
aspect concerns leakage of liquid from the gel, which tends to be very
* P. J. Flory. In:Faraday Discussions 57 (1974) 8.
