Antibacterial Properties of Milk
This page describes the antibacterial properties of 2 minor proteins in milk, Lactoferrin and Lactoperoxidase.
Lactoferrin
Lactoferrin is an iron-binding protein that is found in the milk, saliva, and other body fluids of mammals. Purified lactoferrin has been shown in research studies to have some antibacterial activity against Escherichia coli O157:H7, Listeria monocytogenes, and other foodborne pathogens and spoilage organisms.
Purified lactoferrin (>95%) is produced on a commercial scale from skim milk and cheese whey. Although the natural lactoferrin content of milk is low, the availability of large quantities of milk and whey provide a good source of materials for lactoferrin production. The purification technique uses a high heat pasteurization process (194-212°F (90-100°C) for 5 to 10 min) to inactivate bacteria and viruses that may be present in raw milk. Consequently, the pasteurization conditions used for beverage milk do not destroy the activity of lactoferrin.
Purified lactoferrin is used commercially in infant formula, milk, yogurt, and nutritional supplements. The typical concentration of lactoferrin naturally present in beverage milk is 0.1 g/kg (Walstra et al., 1999). There are currently no reports available in the scientific literature that have evaluated the effectiveness of the natural levels of lactoferrin in milk to prevent against illness from pathogens that may be present in the same milk.
For more information on the antibacterial properties of lactoferrin see references by Dionysius and Milne (1997), Lönnerdal (2003), Shin et al. (1998), Tomita et al. (2002).
Lactoperoxidase
Lactoperoxidase is one of most heat stable enzymes found in milk. Lactoperoxidase has antibacterial activity when it is combined with hydrogen peroxide and thiocyanate. The lactoperoxidase system has been used to reduce spoilage and extend the shelf-life of raw milk in countries where refrigeration may be unavailable (e.g., India ). The lactoperoxidase system has been shown to be effective in reducing the growth of Listeria monocytogenes in raw milk at refrigerator temperatures.
It has been suggested that the presence of lactoperoxidase in raw milk inhibits the disease causing microorganisms (pathogens) present in milk. However, as hydrogen peroxide and thiocyanate must be added to milk in order to activate the system to achieve antibacterial benefits, (since the latter compounds are not naturally present in raw milk), it is unlikely that the lactoperoxidase system contributes significantly to control of pathogens in fresh raw milk.
For more information on the antibacterial properties of the lactoperoxidase system see references by Gaya et al . (1991), Gupta et al. (1986), and Pruitt (2003).