Environmental Engineering Reference
In-Depth Information
sequence), a secondary structure (α-helix and β-sheet substructures), a tertiary
structure (3D structure) and finally a quaternary structure (complex of protein
molecules) (Figure 6.20, right). Their use in forming biomaterials and their ther-
momechanical transformation is therefore more complicated, and their macromo-
lecular structure modification has to be considered. However, there has been
significant research and development during the last decades aimed at texturing
and transforming proteins for food and non-food applications [31]. They can
afford materials with specific properties and, in particular, an increased moisture
resistance when compared with carbohydrate-based materials.
6.3.6.2
Oilseed Proteins
Main developments concerning protein-based materials originated from the
beginning of the century with Ford's research into producing lighter cars using
soybean proteins. The same kinds of operations and materials can be reproduced
with other sources of protein, such as sunflower or rapeseed [32].
The texturation of oilseed proteins is essentially governed through the control
of their denaturation, which is commonly defined as any non-covalent change in
their structure. This loss of structure is relatively similar to the fusion of crystal-
lites in semi-crystalline polymers and may alter the secondary, tertiary or quater-
nary structure of the molecules. Denaturation can be caused by many factors
including heat, pH, dielectric constant and ionic strength.
Once thermal denaturation is achieved, the phenomenon being extremely
dependent on moisture content, polypeptides behave like classical amorphous
polymers undergoing a glass transition at a temperature between 0 and 190°C for
a moisture content between 0 and around 30% (Figure 6.21). Proteins can then
be shaped by hot-pressing, extrusion or injection-moulding. The Iowa State
University research group headed by Jay-Lin Jane has, for example, characterised
many different materials from soybean proteins in the 1990s. The Laboratory of
Agro-Industrial Chemistry has also has characterised all kind of materials from
sunflower proteins in the early 2000s.
6.3.6.3
Cereal Proteins
Cereal proteins such as wheat gluten or corn zein are also interesting candidates
for the production of biomaterials. They are abundant as co-products of the starch
industry; they are well-defined but unfortunately relatively expensive because of
their many possible uses as food additives or encapsulating materials.
Pure zein is odourless, tasteless, hard and water insoluble. Since it is edible, it
has application in processed foods and pharmaceuticals, in competition with chi-
tosan and chitin. Historically it has been used in the manufacture of a wide vari-
ety of commercial products, including coatings for paper cups, soda bottle cap
linings, clothing fabric, buttons, adhesives and binders. It is now used for the
