Enzyme-modifi ed Dairy Ingredients 319- A decrease in molecular weight
- An increase in the number of ionizable
groups, - The exposure of hydrophobic groups hith-
erto concealed
The changes in the functional properties
of a protein are a direct result of these effects.
Food - grade proteolytic enzymes have dif-
ferent pH and temperature optima, and they
hydrolyze a variety of peptide bonds.
Depending on the specifi city of the enzyme,
environmental conditions, and extent of
hydrolysis, a wide variety of peptides are
generated. The resultant protein hydrolyzate
contains low - molecular - weight peptides as
well as higher molecular - weight peptides and
unhydrolyzed proteins. Membrane fi ltration
can be used to fractionate the hydrolyzate
into a low - molecular - weight permeate and a
high - molecular - weight retentate; the func-
tional properties of the two fractions may be
vastly different. In the case of whey proteins,
permeates have been found to have better
foaming and interfacial properties than reten-
tates. However, this additional fi ltration step
decreases yields and increases the production
costs, and should therefore be avoided if
possible.
Proteases, or proteinases, are the most
important class of enzymes from an eco-
nomic viewpoint. Mucor protease coagulates
milk for cheese manufacture. Production of
protein hydrolyzates and fl avoring materials
is discussed below.Improvement in Functional Properties
There is room for improvement in the func-
tionalities of commonly used food proteins,
and physical, chemical, and biological
methods of altering proteins have been
attempted. Among the most interesting and
important is the hydrolysis of proteins by
enzymes, which has been covered exten-
sively. Changes in functionality of proteins
upon hydrolysis result from the reducedconsumed to maintain the pH during hydro-
lysis (the pH stat method); by the depression
of the freezing point, which indicates the
increasing osmolarity (osmometry); or by
the increase in solubility in trichloroacetic
acid. DH values determined by different
methods are often not directly comparable.
Good correlation between base consumption
and soluble - nitrogen content was established
in the case of tryptic hydrolysis of whey
protein. The base consumption and osmom-
etry methods are easy to perform, allow-
ing continuous monitoring of the hydrolysis
process, whereas the estimation of soluble -
nitrogen content using the Kjeldahl method
is time - consuming and cannot be used as an
on - line process control tool. The effects of
enzymatic hydrolysis, using pepsin, Prolase,
or Pronase, on some of the functional prop-
erties of whey protein were reported as early
as 1974.
Infant food formulations are hydrolyzed
to a greater extent, and are classifi ed as
slightly, moderately, or extensively hydro-
lyzed, depending on the molecular weight
distribution of the resultant hydrolyzate.
Extensive hydrolysis is normally used to
produce hypoallergenic hydrolyzates, with
no peptides greater than 5,000 Da and almost
90% of them approximately 500 Da, whereas
hydrolyzates used as protein supplements
may undergo less - extensive hydrolysis.
A commonly encountered problem with
extensively hydrolyzed proteins is bitterness
due to the accumulation of low - molecular -
weight peptides containing hydrophobic
amino acids. This problem can be solved
either by selecting proteases that are not
bitter or by adding specifi c peptidases to de -
bitter the hydrolyzate.
Globular proteins are characterized by
specifi c secondary and tertiary structures
involving disulfi de linkages and hydrophobic
interactions between amino acid residues
within the same molecule or between mole-
cules. Three distinct effects accompany enzy-
matic hydrolysis of proteins: