40 Chapter 2
ride are present in milk as free ions that are
readily diffusible. Their concentrations are
negatively correlated with lactose.
The concentrations of calcium, magne-
sium, ionized phosphate, and citrate depend
on the casein content in the milk. The con-
centration of citrate varies depending on
season and diet of the cow; consequently, this
may affect the soluble calcium content and
milk stability, particularly the equilibrium
between colloidal dispersion and salts. If the
colloidal equilibrium is destabilized, the con-
centration of minerals in milk may affect the
processing and require the addition of anions
to bind to ionic calcium that would restabi-
lize the caseins against aggregation. The con-
centration of calcium in milk is relatively
high; therefore, milk is considered to be an
important source of calcium.Vitamins, Minor Components, and
Micro - nutrients
Milk contains both fat - soluble and water -
soluble vitamins. The concentration of each
vitamin varies depending on the lactation
stage, diet, and the health of the animal. The
fat - soluble vitamins A, D, E, and K are situ-
ated within fat globules. Therefore, low - fat
and skim milk contain smaller concentrations
of fat - soluble vitamins; however, they are
fortifi ed to contain the same concentrations
as whole milk. Vitamin A is important in
vision and bone health. Vitamin D is impor-
tant in bone health and immune system func-
tions, and vitamin E (tocopherol) is an
antioxidant. Vitamin K is present in milk;
however, the amount contained is nutrition-
ally insignifi cant.
The water - soluble vitamins B and C are
present in milk. Milk contains adequate con-
centrations of B vitamins including thiamine,
ribofl avin, niacin, biotin, and folic acid. The
concentration of vitamin C in milk is insig-
nifi cant because it is destroyed by pasteuriza-
tion. Table 2.4 shows the vitamin composition
of various milks.hippuric acid are present in milk in trace
amounts.
Carbohydrates
There are several carbohydrates in milk
including lactose, glucose, galactose, and
glycoconjugates (oligosaccharides, glyco-
proteins, and glycoaminoglycans). The main
carbohydrate in milk is lactose, which ranges
between 4% and 5% of total milk content,
depending on the milk yield and lactation
stage of the cow. The amount of lactose
decreases as the lactation stage advances. It
is a disaccharide comprised of α / β - D - glucose
and β - D - galactose that are linked by a β 1 - 4 -
O - glycosidic bond. Lactose exists in three
forms: α - lactose monohydrate, β - lactose,
and anhydrous α - lactose. The β - lactose form
has the greatest solubility and is sweeter than
the α - lactose forms. Lactose is the major
food source for bacteria during the fermenta-
tion of milk. The bacteria hydrolyse the milk
into glucose and galactose to produce lactic
acid, which inhibits the growth of most other
microorganisms.
Glucose, galactose, and oligosaccharides
are present in relatively small concentrations,
approximately 1 mg/ml.
Trace Elements
There are many trace elements in milk includ-
ing minerals, salts, and vitamins. Their con-
centrations affect several physical properties
including heat stability, electrical conductiv-
ity, the oxidation - reduction potential, and
colligative properties.
Minerals and Salts
Milk contains all minerals considered essen-
tial for human nutrition including potassium
(K), sodium (Na), calcium (Ca), magnesium
(Mg), chloride (Cl), and phosphate esters that
make up between 0.7% and 0.8% of total
milk content. Sodium, potassium, and chlo-