The author is Dairy Officer (Technology), Meat end Dairy Service, FAO, Rome.
Milk from a cow's healthy udder contains only few bacteria. From the time of milking to the time of processing, however, milk will have picked up many more, the amount depending on the standards of milking and milk-handling practices.
The temperature of milk has a significant effect on the rate of bacteria development and, consequently, on the spoilage of milk. It is generally concluded that if the milk is not cooled and does not reach the processor within five hours after milking, it will not be suitable for processing.
There are many areas in the world, particularly in less developed countries, where the cooling of fresh milk is difficult. There is often an unavoidable time-lapse between milking and delivery of the milk to a processing plant or to consumers. During this critical period, deterioration of milk frequently takes place and the result is the loss of large quantities of this most valuable food.
In developing countries, most milk is produced by a large number of smallholders with small quantities of milk, making milk collection and delivery time-consuming and complicated. The more advanced milk collection process found in these countries begins with the producer delivering milk to a collection point where the volume is measured, or the milk weighed, and recorded, and sometimes it is sampled and checked for quality. The milk is later transported, usually by bicycle or donkey, to a larger collection centre where, if possible, it is chilled. The collected milk is subsequently sent in bulk to a processing plant by truck. The time-delay from milking to delivery at the processing plant often exceeds five hours, very negatively affecting the quality of mainly non-refrigerated milk, which is often rejected by dairy processing plants and is also not acceptable to consumers.
In countries with an advanced dairy industry, the bacterial quality of raw milk is safeguarded by cooling during on-farm handling, storage and transportation, which is an effective method of preserving milk quality. In developing countries, on the other hand, this method would be too sophisticated and expensive, or perhaps not even possible. For these countries, it would be more advantageous to have access to alternative methods to protect raw milk from bacterial deterioration during the collection process and transport to the dairy plant (Barabás, 1994)
In most developing countries, the lack of appropriate storage facilities and inadequate transport and communication systems compound the difficulties of preserving locally produced milk, as well as delivering it to processing facilities. This problem is very serious in countries where inappropriate practices and environmental conditions favour the microbial attack on milk and negatively affect its quality during storage, causing deterioration and wastage. Under these circumstances, any possible risks associated with the use of food additives to milk must be weighed against the benefits of preventing milk wastage and increasing its availability to the population.
Developing countries tend to adopt the same rules and/or procedures used in advanced dairy countries, resulting in the introduction of legislation that demands the use of refrigeration in widely scattered milk-producing areas with no technical or economic possibilities for its introduction. This not only impedes the development of milk production, but, even worse, it encourages the consumption of raw milk that has not been properly treated and therefore may be harmful to the consumer.
Unfortunately, it is also true that a more practical approach to the problem of milk treatment is very often hampered by a conservative outlook that finds it easier to refer to existing impracticable rules and regulations than to face reality. It is unrealistic to try to enforce laws that involve the cooling of milk after milking and during storage and, possibly, refrigerated transportation, which, in countries in the early stages of dairy development, are rarely technically and economically feasible (Tentoni, Pastore and Ottogalli, 1968).
For this reason, the use of healthy and suitable preservatives in milk should not only be authorized by local legislation, but also encouraged in those areas where local conditions do not permit, economically or technically, the use of refrigeration in milk collection/storage/delivery schemes. It has been proved that small additions of naturally occurring substances in the lactoperoxidase (LPS) system would stimulate this indigenous antibacterial system in milk and considerably extend its shelf-life.
The use of chemical substances to preserve milk is not a new idea. The problem was first discussed officially at the international level in 1957 at an FAO Expert Consultation held in Rome, Italy. From initial research performed in countries with developed dairy industries and related research, it became clear that the use of the LPS system was one of the most promising methods for the preservation of raw milk.
At the 20th Joint Session of the FAO/World Heath Organization (WHO) Committee of Government Experts on the Code of Principles concerning Milk and Milk Products, held in 1982, the use of the activated LPS system of raw milk was introduced, and the Committee invited the International Dairy Federation (IDF) to provide technical advice. After intensive research, the IDF concluded that the use of the LPS system as an alternative method of preserving raw milk was a completely new and acceptable approach for countries in the early stages of organized dairy-industry development. At its 21st session held in Rome in 1986, the Committee gave IDF the task of preparing the Code of Practice regarding the use of the LPS system as a means of preserving raw milk. The Code of Practice, after being circulated among the national committees of IDF and the Joint FAD/WHO Expert Committee on Food Additives at its 35th meeting in 1989, was finally approved by the Codex Alimentarius Commission during its 19th session, held in July 1991 in Rome (FAD/WHO, 1991).
Regional workshop on raw milk handling and preservation, 13 to 15 September 1994, Alexandria, Egypt: an abstract from the conclusions and recommendations
The workshop provided a valuable opportunity for experts in the region to exchange ideas and information on all areas of milk handling collection and preservation. It was noted with satisfaction that the implementation of milk preservation by activating its antibacterial system. using the lactoperoxidase-hydrogen peroxide-thiocyanate method may greatly benefit all countries in the region.
National participants described the situation in their own countries outlining plans and strategies for milk production on-farm milk handling milk collection systems milk quality control and legislation and discussed policy options for encouraging support, research activities and methodologies for the implementation of the milk preservation method in their home countries.
The participants urged FAO and governments in the region to otter their fullest possible support for the introduction of the method mainly in remote areas in accordance with the Code of Practice approved by Codex Alimentarius.
The workshop recognized that most locally produced milk comes from smallholders who have very limited possibilities for the proper handling of raw milk and that as a result activities hi raw milk preservation should be directed mainly towards this group.
It was also recommended that a cooperative network of specialists and institutions be established in the region for the expansion of the lactoperoxidase method for raw milk preservation and for the exchange of results obtained in field application of the method.
The workshop expressed special thanks to FAO for its technical guidance and to the University of Alexandria for the preparation of the workshop.
LPS is a protein naturally present in milk. One of its unique biological functions is an antibacterial/enzyme effect working only in the presence of hydrogen peroxide and thiocyanate. Both these substances are naturally present in raw milk in different concentrations, but they need to be adjusted. The method of activating LPS in raw milk is based on increasing insufficient levels of thiocyanate present in milk to about 15 ppm and subsequently adding an equimolar amount (8.5 ppm H2O2) of hydrogen peroxide. This amount of hydrogen peroxide is approximately 100 times less than that often used for the unauthorized conservation of milk. And the level of thiocyanate mentioned above is, for example, three to 20 times lower than that found in human saliva or in some vegetables, such as cassava and cabbage. In refrigerated milk, this treatment resulted in an antibacterial effect lasting five to six days (Björk, Claesson and Schulthes, 1979), and the shelf-life of raw milk in an ambient temperature was increased to seven to eight hours at 30°C (Claesson, 1994; Patel and Sannabhadti, 1993). Toxicological investigations using high doses of thiocyanate showed that if the level of thiocyanate was kept in accordance with the Code of Practice, there would be no health problems.
Field trials in Kenya, Nicaragua, Sri Lanka, Mexico, the Philippines, Pakistan and Cuba carried out by national research institutes with the cooperation of the Swedish University of Agricultural Science and FAO demonstrated a significant improvement in the quality of raw milk in these countries (Korhonen, 1980; Ponce et al., 1992; Barraquio et al., 1993; Amjad and Faqir, 1993; Lambert, 1993).
The LPS method is fully effective, cheap, safe and applicable at milk collection points and can prolong the shelf-life of unrefrigerated milk up to three or four hours more than that of untreated milk. The duration of prolongation depends, of course, on the initial quality of the raw milk and on when the treatment was carried out. This additional conservation time is often essential for the safe delivery of milk of an appropriate quality to processing centres. If necessary, this method could also be used for preserving already refrigerated milk for extended periods, even in countries where refrigeration facilities are well established.
In countries with a warm climate, the alternative method of milk preservation - application of the LPS system - has great potential. Since it is recommended by the IDF Code of Practice, it is an important package of appropriate technologies, easily integrated into existing milk collection systems. It would also enable the expansion of milk collection into remote areas, where it has not been feasible under present conditions.
The LPS system is an antibacterial system created by nature to protect both human and animal organisms. The use of this system through appropriate methodology and application at milk collection systems in developing countries is a good example of an applied biotechnological process that has great potential for wide field application. FAO is actively involved in exploring opportunities to exploit this potential for the benefit of milk producers in remote areas of developing countries. In September 1994, FAO organized a regional workshop on the subject, and an abstract of its conclusions and recommendations is published here (see Box).
Amjad, A. & Faqir, M.A. 1993. Milk preservation by chemical methods. Final report. University of Agriculture, Faisalabad, Pakistan.
Barabás, J. 1994. Milk hygiene with particular reference to milk handling and preservation. Proc. Regional Workshop on Raw Milk Handling and Preservation, University of Alexandria, Egypt.
Barraquio, V.L., Resubal, L.E.M., Bantoc, I.B.M. & Almazan, E.N. 1993. A study on milk preservation by chemical methods. University of the Philippines, Los Baños, the Philippines.
Björk, L., Claesson, O. & Schulthes, W. 1979. The lactoperoxidase/thiocyanate/hydrogen peroxide system as a temporary preservative for raw milk in developing countries. Milchwissenschaft, 34(12): 726-729.
Claesson, O. 1994. The lactoperoxidase/thiocyanate/hydrogen peroxide system. Proc. Regional Workshop on Raw Milk Handling and Preservation, University of Alexandria, Egypt.
FAO/WHO. 1991. Codex Alimentarius Commission. 19th Session of the Codex Alimentarius Commission, Rome, 1-10 July 1991. Alinorm 91/13.
Korhonen, H. 1980. Paper presented at the seminar on milk preservation held in Nairobi, Kenya, by Alfa Laval AB, Tumba, Sweden.
Lambert, J.-C. 1993. The lactoperoxidase system. Experiences from Cuba, the Philippines and Pakistan. Proc. Sem. Dairy Development Policy and Implementation, Harare, Zimbabwe.
Patel, D.A. & Sannabhadti, S.S. 1993. Effect of activation of lactoperoxidase system and heating to thermization temperature on shelf-life of buffalo raw milk. Indian J. Dairy Sci., 46(11): 529-533.
Ponce, P., Capdevilla, Y., Alfonso, H.A., Lopez, M.G., Leon, R. & Taboada, A. 1992. Conservación de la leche en Cuba mediante la activación del sistema lactoperoxidasa. Wld Anim. Rev., 73: 31-41.
Tentoni, R., Pastore, M. & Ottogalli, G. 1968. Hydrogen peroxide for milk collection under difficult conditions. Annali di microbiologia ed enzymologia, p. 85-123.