2009_Book_FoodChemistry

80 1 Amino Acids, Peptides, Proteins
and requirements of food processing operations is
a perennial endeavor. Food production is similar
to a standard industrial fabrication process: on
the one hand is the food commodity with all
its required properties, on the other hand are
the components of the product, each of which
supplies a distinct part of the required properties.
Such considerations have prompted investigations
into the relationships in food between
macroscopic physical and chemical properties
and the structure and reactions at the molecular
level. Reliable understanding of such relationships
is a fundamental prerequisite for the design
and operation of a process, either to optimize
the process or to modify the food components to
meet the desired properties of the product.
Modification of proteins is still a long way from
being a common method in food processing, but it
is increasingly being recognized as essential, for
two main reasons:
Firstly, proteins fulfill multipurpose functions in
food. Some of these functions can be served betterbymodifiedthanbynativeproteins.
Secondly, persistent nutritional problems the
world over necessiate the utilization of new raw
materials.
Modifying reactions can ensure that such new
raw materials (e. g., proteins of plant or microbial
origin) meet stringent standards of food safety,
palatability and acceptable biological value. A review
will be given here of several protein modifications
that are being used or are being considered
for use. They involve chemical or enzymatic
Table 1.35. Properties of protein in food
Properties with
methods or a combination of both. Examples have
been selected to emphasize existing trends. Table
1.35 presents some protein properties which
are of interest to food processing. These properties
are related to the amino acid composition and
sequence and the conformation of proteins. Modification
of the properties of proteins is possible
by changing the amino acid composition or the
size of the molecule, or by removing or inserting
hetero constituents. Such changes can be accomplished
by chemical and/or enzymatic reactions.
From a food processing point of view, the aims of
modification of proteins are:
• Blocking the reactions involved in deterioration
of food (e. g., the Maillard reaction)
• Improving some physical properties of proteins
(e. g., texture, foam stability, whippability,
solubility)
• Improving the nutritional value (increasing the
extent of digestibility, inactivation of toxic or
other undesirable constituents, introducing essential
ingredients such as some amino acids).
1.4.6.2 Chemical Modification
Table 1.36 presents a selection of chemical reactions
of proteins that are pertinent to and of current
importance in food processing.
1.4.6.2.1 Acylation
Treatment with succinic anhydride (cf. 1.4.4.1.3)
generally improves the solubility of protein.
nutritional/physiological
relevance
Amino acid composition
Availability of amino
acids
processing relevance
Solubility, dispersibility
Ability to coagulate
Water binding/holding
capacity
Gel formation
Dough formation,
extensibility, elasticity
Viscosity, adhesion,
cohesion
Whippability
Foam stabilization
Emulsifying ability
Emulsion stabilization
Table 1.36. Chemical reactions of proteins significant
in food
Reactive Reaction Product
group
NH 2 Acylation –NH–CO–R
NH 2 Reductive
alkylation
with HCHO N(CH 3 ) 2
CONH 2 Hydrolysis COOH
COOH Esterification COOR
OH Esterification O CO R
SH Oxidation S S
S S Reduction SH
CO NH Hydrolysis COOH + H 2 N