Agriculture Reference
In-Depth Information
viscosifi ers that replace carbohydrates or replace chemical preservatives as natural
preservatives. Examples of proteins as emulsifi ers and foaming agents are also
given.
9.3.1 Protein-based viscosifi ers
Gums and polysaccharides are generally used to increase the viscosity of food
products and, thereby, act as viscosifi ers or stabilizers. Stabilizers are added to
food products to avoid sedimentation of particles or creaming of emulsion droplets
by increasing the viscosity of the product. Although these gums and polysaccharides
are extracted from natural products they carry an E number. Examples are
carrageenans extracted from the red seaweeds (E407), xanthan gum obtained by
fermentation (E415), modifi ed starches from different crops (E14xx) and modifi ed
celluloses from plant materials (E46x).
The viscosity increasing properties of these gums originate from their large
size (molecular weights of 500 kDa and above). As such these large molecules
occupy a large volume as they often form random coil or rod-like structures. In
contrast, most proteins are small molecules (molecular weight of 10-50 kDa),
which occupy less volume and, thus, contribute less to the viscosity of a production.
In addition, globular proteins are folded in a compact globular shape, which
reduces the impact on the viscosity even further. On the other hand, storage
proteins (from plants) are often aggregated into dense, insoluble protein particles
that also do not contribute to the viscosity. To apply proteins as a general source
of viscosifi ers, their functionality has to be tailored beforehand.
Tailoring proteins to increase their viscosifying functionality aims to increase
the volume occupied by the protein molecules. Therefore, tailoring has to result in
structuring of the proteins in such a way that they form open aggregates or stiff
linear aggregates. Special attention has to be paid obtaining transparent solutions,
as proteins generally tend to result in turbid (particle) gels, whereas gums are
generally desired for their transparent behavior. The protein source plays an
important role in the selection of the structuring methods. Proteins from different
sources have naturally different degrees of structuring. For example, soluble
proteins, such as globular proteins from dairy or egg, require an aggregation step
to create structures, whereas poorly soluble proteins (extensively aggregated)
such as storage proteins need extrusion or hydrolysis to improve their structural
properties. The impact of the degree of aggregation/organization of the protein
ingredient on the required structuring method is shown schematically in Fig. 9.2.
Examples of protein structuring to obtain protein-based viscosifi ers are described
below.
Structuring proteins into long fi brillar structures using heat treatment is a
natural process that maintains the clean label status of the proteins while increasing
their functionality. Understanding the molecular properties of the protein
ingredient is key to selecting the optimal processing conditions. Close to their
isoelectric point, proteins tend to form random aggregates upon heating. Addition
of salts also enhances the formation of random aggregates. Thus, repulsive
￿ ￿ ￿ ￿ ￿
Search WWH ::




Custom Search