Proteins as clean label ingredients in foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 201

(pH 4-5). Subsequently, the precipitated protein curd is collected by centrifugation
and usually neutralized with alkali to form the sodium salt of the protein before
drying. Based on the fi nal protein content of the product obtained, the material is
classifi ed as soy protein concentrate or isolate.
As previously stated, proteins in this category exist as complexes of globular
proteins and are sensitive to denaturation during processing. The source material
for the extraction of these storage proteins is a by-product of the oil production
from legumes. Therefore, before protein extraction starts, the protein fraction will
already have been exposed to conditions that result in protein denaturation. As a
consequence, the industrial manufacturing of storage proteins results in protein
preparations characterized by an excessive aggregation (Utsumi et al. 1997;
Renkema 2001).

9.2.5 Gluten
Grains (including wheat) contain a third type of storage protein called gluten or
'prolamines'. Gluten is a composite of the proteins gliadin (45%) and glutenin
(55%). Gliadins are monomeric proteins and glutenins are a mixture of polymers.
Together, gliadin and glutenin comprise about 80% of the protein present in wheat
seed. In contrast to the proteins from the other four categories, gluten is water-
insoluble. The storage proteins of maize and rice are sometimes called glutens,
but their proteins differ from wheat gluten by lacking gliadin.
The process for the extraction of gluten is relatively old and based on the
water-insolubility of gluten. A dough is made by adding water to the fl our and
then kneaded. Subsequently, the dough is washed with water to separate the gluten
fraction from the starch fraction and other proteins (albumin/globulin). The fi nal
step, drying, is the quality-determining step for the techno-functionality of the
gluten protein.
The well-known viscoelastic properties of dough are determined by the gluten
proteins, gliadin and glutelins, as a result of their covalent (disulfi de cross-linking)
and non-covalent interactions. The glutelin fraction is a mixture of polymers that
differ in sizes (high-molecular and low-molecular fraction). The type and amount
of these fractions determine to a large extent the rheological properties of dough
(MacRitchie and Lafi andra 1997; Hamer 2003).

￿ ￿ ￿ ￿ ￿

9.3 Examples of applications of proteins in foods
and beverages
Proteins are generally used in food products for their nutritional value and
technological functionality. The use of proteins as a source of clean label
ingredients is related to their technological functionality. In this section the
concept of using proteins as clean label ingredients is limited to those protein
ingredients developed to fulfi ll a specifi c functionality in a food product and
thereby replace current ingredients. Examples are given of proteins as clean label