MARKET MILK

Module 5. Physico-chemical, microbiology and nutritional properties of milk

Lesson 13
MICRO COMPONENTS OF MILK

13.1 Vitamins

Vitamins are organic substances that are essential to normal life processes, but cannot be synthesized by the body. They occur in very small concentrations in both plants and animals. Milk is a good source of vitamins (Table 13.1). Milk contains the fat soluble vitamins A, D, E, and K. As milk fat is an important dietary source of vitamin A, low fat products are normally supplemented with this vitamin. The content of Vitamin D, which also aids in the absorption of calcium, is influenced by the feed of the animals. Milk is a fair source of vitamin E. It is also a fairly good source of water soluble B vitamins such as thiamine (B₁), riboflavin (B₂), niacin (B₃), pantothenic acid (B₅), pyridoxine (B₆) and cyanocobalamin (B₁₂). Milk is, however, a poor source of vitamin C (ascorbic acid). The little quantity of vitamin C that is present in raw milk is very heat-labile and easily destroyed by pasteurization.

Table 13.1 Vitamin content of fresh milk (per 100 g)

Average derived from different sources, ND – no data available

13.2 Minerals

All 22 minerals considered essential to the human diet are present in milk (Table 13.2). Milk is an important source of dietary calcium, magnesium, phosphorus, potassium, selenium, and zinc. In milk, approximately 67% of the calcium, 35% of the magnesium, and 44% of the phosphate are bound to salts within the casein micelle and the rest are soluble in the serum phase. Milk contains very small amounts of copper, iron, manganese and sodium. Other minerals such as aluminium, boron, zinc, cobalt, iodine, fluorine, molybdenum, nickel, lithium, barium, strontium and silica are also present in milk, but in minute amounts.

Table 13.2 Mineral content of milk (per 100 g)

Average derived from various sources, ND – no data available

13.3 Lactoferrin

Lactoferrin (LF) is a single-chain, metal-binding glycoprotein. It is a red coloured iron-binding protein and may also mediate some effects of inflammation and have a role in regulating various components of the immune system. It has antibacterial, antifungal, anti-endotoxin, and antiviral activities. It inhibits enteropathogenic organisms due to its ability to bind iron, as iron is an essential nutrient often required for bacterial growth. It promotes the growth of beneficial bacteria such as bifidobacteria. Lactoferrin is an anti-oxidant that naturally occurs in many body secretions such as tears, blood, breast milk, saliva and mucus. Lactoferrin in milk might play a role in iron absorption and/or excretion in newborns, as well as in promotion of intestinal cell growth. Its level in human milk is about 1 g/L and in human colostrums, about 7 g/L. As the levels of this protein in cow milk is only about one-tenth of that in human milk, this has caught the attention of those involved in designing human milk replacement formulae.

13.4 Lactoperoxidase

Lactoperoxidase is an oxido-reductase enzyme that occurs in milk, saliva, tears, cervical mucus. It is a single polypeptide chain with a molecular weight of 77,000 – 100,000. It is a relatively heat resistant enzyme whose activity remains sufficient even after pasteurization. Cow milk has 1.4 units/ml of lactoperoxidase, whereas buffalo milk has 0.9 units/ml. The thermal stability of buffalo milk lactoperoxidase is higher than that of cow milk. Lactoperoxidase has been widely researched for its ability to preserve raw milk. The amount of this enzyme required for preservation is 0.5-1 mg/L, much lower than its concentration in cow milk (30 mg/L).
13.5 Lysozyme

Lysozyme is an enzyme that is abundantly present in the mucosal membranes that line the human nasal cavity and tear ducts. It can also be found in high concentration in egg white. Lysozyme destroys bacterial cell walls by hydrolyzing the polysaccharide component of the cell wall. Human milk contains 0.4 g/L of lysozyme, an enzyme that contributes to antibacterial activity in human milk. Lysozyme content of buffalo milk is 15.2 µg/100 ml which is lower than cow milk. Although lysozyme from egg white had found more industrial applications in the past, it has now been recognized that the enzyme isolated from human or bovine milk has far greater lytic activity compared to egg lysozyme.

Selected Readings

McSweenwy, P.L.H. and Fox, P.F. 2009. Eds. Advanced Dairy Chemistry. Volume 3. Lactose, Water, Salts and Minor Constituents. Springer Publications, USA.
Robert Jenness, R., Noble P. Wong, N.P. and Elmer H. Marth, E.H. 1999. Fundamentals of Dairy Chemistry. Aspen Publishers, USA.