Food Biochemistry and Food Processing

19 Chemistry and Biochemistry of Milk Constituents 449

nate. Cows’ milk is a very significant source of vita-
mins, especially biotin (B 7 ), riboflavin (B 2 ), and
cobalamine (B 12 ), in the human diet. Typical con-
centrations of all the vitamins and the percent of
RDA supplied by 1 L of milk are shown in Table
19.4. For general information on the vitamins see
Schaafma (2002); for specific aspects in relation to
milk and dairy products, including stability during
processing and storage, the reader is referred to a set
of articles in Roginski et al.(2002).
In addition to their nutritional significance, four
vitamins are of significance for other reasons, which
have been discussed in the subsection Fat-Soluble
Vitamins, above.

• Vitamin A (retinol) and especially carotenoids
  are responsible for the yellow-orange color
  of fat-containing products made from cows’
  milk.


• Vitamin E (tocopherols) is a potent antioxi-
  dant.


• Vitamin C (ascorbic acid) is an antioxidant or
  prooxidant, depending on its concentration.


• Vitamin B2 (riboflavin), which is greenish-
  yellow, is responsible for the color of whey or
  UF permeate. It cocrystallizes with lactose and is
  responsible for its yellowish color, which may be
  removed by recrystallization or bleached by
  oxidation. Riboflavin acts as a photocatalyst in
  the development of light-oxidized flavor in milk,

which is due to the oxidation of methionine (not

to the oxidation of lipids).

SUMMARY

Milk is a very complex fluid. It contains several hun-

dred molecular species, mostly at trace levels. Most

of the microconstituents are derived from blood or

mammary tissue, but most of the macroconstituents

are synthesized in the mammary gland and are milk

specific. The constituents of milk may be present in

true aqueous solution (e.g., lactose and most inorgan-

ic salts), in a colloidal solution (proteins, which may

be present as individual molecules or as large aggre-

gates of several thousand molecules, called micelles),

or as an emulsion (lipids). The macroconstituents can

be fractionated readily and are used as food ingredi-

ents. The natural function of milk is to supply the

neonate with its complete nutritional requirements

for a period (sometimes several months) after birth

and with many physiologically important molecules,

including carrier proteins, protective proteins, and

hormones.

The properties of milk lipids and proteins may be

readily modified by biological, biochemical, chemi-

cal, or physical means and thus converted into novel

dairy products.

In this chapter, the chemical and physicochemical

properties of milk sugar (lactose), lipids, proteins,

and inorganic salts are discussed. The technology

Table 19.4.Typical Concentrations of Vitamins in Milk and Proportion of RDA Supplied by 1 L
Milk

Vitamin Average Level in 1 L Milk % RDA in 1 L Milk

A 380 retional equivalents 38
B 1 (thiamine) 0.4 mg 33
B 2 (riboflavin) 1.8 mg 139
B 3 (niacin) 9.0 niacin equivalents 53
B 5 (pantothenic acid) 3.5 mg 70
B 6 (pyridoxine) 0.5 mg 39
B 7 (biotin) 30 g 100
B 11 (folic acid) 50 g1 3
B 12 (cobalamin) 4 g 167
C 15 mg 25
D 0.5 g1 0
E 1 mg 10
K 35 mg 44

Source:Adapted from Schaafma 2002.