Food Chemistry

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 investiga-
tions into the relationships in food between
macroscopic physical and chemical properties
and the structure and reactions at the molecular
level. Reliable understanding of such relation-
ships 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 bet-
terbymodifiedthanbynativeproteins.
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 re-
view will be given here of several protein modi-
fications that are being used or are being consid-
ered for use. They involve chemical or enzymatic

Table 1.35.Properties of protein in food

Properties with

nutritional/physiological processing relevance
relevance

Amino acid composition Solubility, dispersibility
Availability of amino Ability to coagulate
acids Water binding/holding
capacity
Gel formation
Dough formation,
extensibility, elasticity
Viscosity, adhesion,
cohesion
Whippability
Foam stabilization
Emulsifying ability
Emulsion stabilization

methods or a combination of both. Examples have

been selected to emphasize existing trends. Ta-

ble 1.35 presents some protein properties which

are of interest to food processing. These proper-

ties are related to the amino acid composition and

sequence and the conformation of proteins. Modi-

fication 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 accom-

plished 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 deteriora-
  tion of food (e. g., theMaillardreaction)


• Improving some physical properties of pro-
  teins (e. g., texture, foam stability, whippabil-
  ity, solubility)


• Improving the nutritional value (increasing the
  extent of digestibility, inactivation of toxic or
  other undesirable constituents, introducing es-
  sential ingredients such as some amino acids).

1.4.6.2 ChemicalModification...................................

Table 1.36 presents a selection of chemical reac-

tions of proteins that are pertinent to and of cur-

rent 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.

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