Proteins as clean label ingredients in foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 199

process, part of one type of casein is split off resulting in destabilization of the
casein micellar structure. After drying and milling rennet-casein is obtained.
Acidifi cation of milk to pH 4.6 leads to disintegration of the micellar structure
(solubilization of calcium phosphate) and selective precipitation of the casein
fraction. After washing, the casein dispersion is re-solubilized by neutralization.
After drying and milling, caseinate is obtained. Acid casein is prepared by omitting
the neutralization step. The different caseinate types differ mainly with respect to
the type of counter-ion and salt content.
Rennet and acid casein are water-insoluble and have therefore a limited
application range. Caseinates are applied for a wide variety of applications related
to their unique physicochemical properties. All caseins have a distinct amphiphilic
character. They lack a rigid secondary structure, and have a tendency to associate
and interact with bi- and trivalent metal ions. Because they lack secondary and
tertiary structure they are relatively insensitive to heat treatments. Their amphiphilic
character and the lack of secondary structure (rheomorphic character) form the
basis for their emulsifying and foam stabilizing functionality. The self-association
properties and their ability to interact with metal ions are responsible for the
structuring properties of caseins (Rollema, 2003; Rollema and de Kruif 2003).

9.2.3 Globular, monomeric proteins
While the other four categories of food proteins are associated with a specifi c
source material (e.g. gelatin is produced from collagen), the globular proteins can
be derived from a variety of source materials, both animal and vegetable. Globular
proteins are defi ned as proteins having a spherical structure, induced by the
protein's tertiary structure. The apolar (hydrophobic) regions bend inwards
towards the molecule's interior whereas polar (hydrophilic) regions are exposed
outwards, allowing dipole-dipole interactions with a solvent, which explains the
aqueous solubility of globular proteins. Globular food proteins are extracted from
a wide range of source materials. Examples are whey proteins from milk,
ovalbumin from egg, patatin from tuber (potato) and serum albumin from blood.
Extraction is mainly based on isoelectric precipitation and/or fi ltration and
chromatography techniques at aqueous conditions.
In their natural habitat globular proteins can display a variety of functionalities
(enzymes, hormones, storage, nutritional). For their application as food ingredients
their functional properties are related to their physical, chemical and conformational
properties (Damodaran 1997). Therefore, they depend not only on their intrinsic
properties but also on their degree of denaturation, or more generally speaking on
the changes in the protein's tertiary structure. Denaturation of globular proteins is
in most cases a prerequisite to 'activate' the functionality that is desired for the
sensorial and textural properties of food. Denaturation has been defi ned as a major
change of the very specifi c native protein structure without alteration of the amino
acid sequence (Tanford 1968) and is a consequence of an altered balance between
the different forces, such as electrostatic interactions, hydrogen bonds, disulfi de
bonds, dipole-dipole interactions and hydrophobic interactions, which maintain a

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