nutritional and functional properties of whey and lactose

WHEY PROTEINS
They possess solubility; create
viscosity through water binding;
form gels; emulsify; bind fat; facilitate
whipping, foaming and aeration; enhance
color, flavor and texture; and bring with
them numerous nutritional benefits as
noted in the previous section.
Milk proteins are often divided into
two broad classes: caseins and whey
proteins. Approximately 80% of the
proteins in milk are caseins, and these
are coagulated and separated as the
cheese curd (see Table 6).
The whey proteins (also called
milk serum proteins) are the proteins
that remain soluble when caseins
are coagulated by either enzyme
or acid. The whey proteins include
beta-lactoglobulin, alpha-lactalbumin,
blood serum albumins, immunoglobulins
and protease-peptones fractions. Part
of the protease-peptones have been
identified as proteolytic degradation
products of beta-casein.
The heat-sensitive whey proteins (betalactoglobulin,
alpha-lactalbumin, blood
serum albumins and immunoglobulins)
differ in molecular weights and properties
such as isoelectric points (see Table 7).
The functional properties of whey
proteins are influenced by a number
of compositional and processing
variables including:
■ pH 12
■ Calcium ion concentration
■ Salt concentration
■ Previous heat treatments
■ Residual lipid content
■ Protein concentration
The term pH stands for the potential
hydrogen ion concentration in a solution.
At pH 7.0, the number of hydrogen and
hydroxyl ions in solution are equal to
each other, and the solution is neutral.
At pH values below 7.0, the number of
hydrogen ions exceeds the hydroxyl ions,
and the solution is acidic. At pH values
above 7.0, the number of hydroxyl ions
exceeds the hydrogen ions, and the
solution is alkaline.
Proteins make
up approximately
0.78% of fluid whey
and 11%–13% of solids
in dried whey. Whey
proteins are important
components of whey
because they possess
a host of functional
properties that make
them invaluable
food ingredients.
12The pH values increase logarithmically.
A pH 4.0 solution is 10 times as acid
as a pH 5.0 solution, and 100 times
as acid as a pH 6.0 solution. As the
concentration of hydrogen ions in
solution increases, the negative charge
on the proteins is neutralized. At the
pH identified as the isoelectric point
for a protein, the charge on the protein
becomes neutral, and the proteins will
not migrate in an electric field. At this
pH, the physical properties of proteins
(solubility, conductivity, stability and
degree of hydration) are at a minimum.
Table 6
Concentration of Major Milk Proteins
Approximate
% of Total
Protein Concentration (g/l) Protein
Caseins 24–28 80
• alpha-casein 15–19 42
• beta-casein 9–11 25
• kappa-casein 3–4 9
• gamma-casein 1–2 4
Whey proteins 5–7 20
• beta-lactoglobulin 2–4 9
• alpha-lactalbumin 1–1.5 4
• protease-peptones 0.6–1.8 4
• blood proteins 1.4–1.6 2
serum albumin 0.1–0.4 1
immunoglobulins 0.6–1.0 2
100
Table 7
Characteristics of Heat-Sensitive Proteins
in Cheese Whey
Approximate
% of Whey Molecular Isoelectric
Protein Proteins Weight Point
• beta-lactoglobulin 48 18,400–36,800 5.2
• alpha-lactalbumin 19 14,200 5.1
• Protease-peptones* 20 4,000–80,000 5.1–6.0
• Blood proteins: 13 69,000 4.8
serum albumin 5 69,000 4.8
immunoglobulins 8 160,000 5.5–6.8
100
*Degradation products of various milk proteins including beta-caseins.
Source: de Wit, 1981; Harper, 1984.
Source: Fennema, 1965.
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