THE SHELF LIFE OF MILK
While there is little controversy over many aspects of product development, food quality issues and safety processes must be taken into consideration. Critical discussion of biotechnology and its application in the food marketplace has resulted in a firestorm of public debate, scientific discussion, and media coverage. The countries most affected by this debate are Middle Eastern and third world countries, who stand to reap the benefits of solving widespread starvation, and countries such as the United States. The world’s population is predicted to double in the next 50 years and ensuring an adequate food supply for this booming population is already a challenge. Scientists must meet the challenge through the production of food products that meet the highest quality issues and follow intense safety processes. Milk is an important food product that is an essential part of a healthy diet, although this product appears to have a relatively short shelf life once the container is opened. This paper will analyze the shelf-life of milk, taking onto consideration the quality issues surrounding safety in the milk-manufacturing process.
Benefits of Milk
Milk, a natural liquid food, is one of the most nutritionally complete foods, adding high-quality protein, fat, milk, sugar, essential vitamins and minerals to one’s diet. Milk contains bacteria that, when improperly handled, may create conditions where the bacteria can multiply. The microorganisms that constitute bacteria can find their way to the hair, udder, and teats of dairy cows and can move up the teat canal. Some of these germs cause an inflammatory disease of the udder called mastitis while others enter the milk without causing any harm to the animal. In addition, organisms can enter the milk supply during the milking process when equipment is used in milking, transporting, and storing the milk is not properly cleaned and sanitized. All milk products have the potential to transmit disease causing organisms to humans. Ironically, the nutritional components that make milk and milk products an important part of the diet also support the growth of organisms. In addition, milk is only good for a certain period of time; after this time frame, it becomes spoiled and potentially dangerous.
The “shelf-life” of a product is defined as the length of time that a food can be held under recommended or practical storage conditions and still maintain its freshness or acceptable quality (Cornell University, 2000). The shelf-life of milk is reflected in the “sell by” date, while many products stay fresh for a short period of time, consisting of days, after this date. Milk is commonly referred to in two different ways; pasteurized and ultra-pasteurized. Both pasteurization and ultra-pasteurization refer to the heat processes that are designed to kill bacteria, or germs, in milk that may be harmful or may cause spoilage of milk products. These kinds of bacteria can be found in raw milk directly from the farm; as a result milk from farms is transported to dairy processing plants and is heat processed within a few days after milking to prolong its shelf-life.
Drinking raw milk causes foodborne illnesses, which have occurred worldwide since cows have been milked. Historically, cows have been milked in farms as far back as 9000 B.C., however, it was not until colonial times in 1611 that dairy cows were raised (Shearer, et.al., 1992). During this period, the majority of cows were used for dairy and beef purposes, and milk and dairy products were unavailable for those not living on or near the farm. Milk production was seasonal, and the stabilization of this production was precluded as a result of the lack of refrigeration
History of Milk Processing
Over the years, the modern technology involved in milk processing have rectified these problems and in the present-day a wide array of safe, wholesome dairy products are available to people throughout the developed world (Shearer et.al., 1992). The production of quality milk affects consumers, retail distributors of milk, milk product processors, and state regulatory departments. In the 1900’s it was discovered that milk can transmit tuberculosis, scarlet fever and diphtheria to humans; the threat of these diseases and the incidence of outbreaks involving milk have been drastically reduced over the decades of the past as a result of improved sanitary milk production practices and pasteurization. Pasteurized milk is milk that has been heated to a minimum of o161 degrees Fahrenheit for a minimum of 15 seconds, and packaged under clean and sanitized conditions. Some bacteria will survive under pasteurization in very low numbers, though they are not considered harmful and will not spoil milk under normal refrigerated conditions (Cornell University, 2000). Pasteurized milk that spoils quickly is most often the result of contamination after the pasteurization process. The average shelf-life of pasteurized milk held under proper refrigeration is 12 to 16 days (Cornell University, 2000). Under ideal refrigeration, most pasteurized milk will remain fresh for 2 to 5 days after its sell by date (Cornell University, 2000).
Ultra-pasteurized milk is milk that has been heated to a minimum of 280 degrees Fahrenheit for a minimum of 2 seconds. This temperature and time kills virtually all spoilage bacteria in milk. Ultra-pasteurized milk is packaged under near sterile conditions, which makes contamination with spoilage bacteria unlikely and rare (Cornell University, 2000). Ultra-pasteurization is most often used for specialty diary products and has an average shelf-life of 30 to 90 days when held under refrigeration, but only until the product is opened. Once an ultra-pasteurized product is opened, it may become contaminated with spoilage bacteria, so after opening, it ultra-pasteurized milk should be kept well refrigerated and used within 7 to 10 days for best quality.
Milk Safe Handling
There are three main requirements for the safe handling of milk: 1) a potable water supply and proper dispensing system must be available to avoid contamination, 2) clean and healthy animals, clean hands, and clean utensils, and 3) rapid cooling, cold storage, proper pasteurization, and clean storage of pasteurized milk. The first requirement consists of a pure hot and cold water supply for the animals’ health, and for proper cleaning of the animals, milk handles and utensils, along with regular maintenance of the system. Additionally, the animal’s hair should be clipped regularly around the flanks and udder to prevent it from collecting dirt. For the second requirement, milkers should wash their hands and the udder with clean water or use an approved germicidal solution before milking. Most importantly, milk from diseased animals or those under antibiotic treatment may not be used. All equipment and utensils should be cleaned immediately after use. Finally, milk must be promptly cooled to 40 degrees Fahrenheit or less and stored in a closed container before and after pasteurization to maintain the quality and flavor of the milk.
After the milk is taken from the cow, it continues through further handling and processing. Milk processing has three main objectives: 1) the destruction of human pathogens through pasteurization, 2) keeping the quality of the product without significant loss of flavor, appearance, physical and nutritive properties, and 3) the selective control of organisms which may produce unsatisfactory products (Shearer et.al., 1992). The procedures at milk processing plants prevent further bacterial contamination of raw materials, reduce bacterial numbers in milk, and protect the finished product from recontamination through careful handling, proper packaging and storage. Certain organisms are capable of surviving pasteurization and refrigeration processes, which an important concern because they reduce the product’s shelf-life. The bacteria of most concern are psychrotropic bacteria, which can grow at refrigeration temperatures and can produce off-flavors. The primary source of these bacteria is in the environment, such as air, dust and dirty equipment, so the proper cleaning and sanitizing procedures are necessary for quality control. Grade A milk quality standards allow a maximum of 100,000 bacteria per milliliters of raw milk (Shearer at.al., 1992). Chronic offenders of this standard risk losing their license to sell milk to the Grade A market, and the majority of dairies are able to maintain bacteria counts between 5 to 10,000 per milliliter.
Dairy cooperatives are organized by dairymen for the purpose of marketing milk, and instead of buying milk directly from the farms, milk processors buy their milk directly from the dairy cooperative.
Cooperatives serve the dairymen by promoting dairy products, providing an effective lobby for political concerns, and informing members on issues such as water quality, waste management, and milk pricing. Other state departments are responsible for the safe production of milk as well. The United States Public Health Service promotes the consumption of milk for good nutrition, recognizes that the potential for milkborne illnesses is a significant public health threat, and has agreements for reciprocal acceptance of milk and milk products between political jurisdictions. The milk sanitation program of the United States Public Health Service has been very successful; in 1938, milkborne disease outbreaks constituted 25% of all disease outbreaks resulting from infected foods and contaminated water supplies. Today, less than 1% of such disease outbreaks can be linked to the consumption of milk and milk products (Shearer et.al., 1992).
However, although fewer cases of milkborne ailments exist today, the possibility is still realistic. For example, more than 300 people in the United States got sick from drinking raw milk or eating cheese made from raw milk in 2001, and nearly 200 became ill from these products in 2002 (Bren, 2004). Most health people recover from foodborne illnesses within a short period of time, but others may have symptoms that are chronic, severe, or life-threatening. Individuals with weakened immune systems, such as the elderly, children and those with certain diseases or conditions, are most at risk for severe infections from pathogens that may be present in raw milk. In pregnant women, listeria monocytogenes caused illnesses that resulted in miscarriage, fetal death, or the illness or death of a newborn infant (Bern, 1994). Furthermore, escherichia coli infection has been linked to hemolytic uremic syndrome, a condition that can cause kidney failure and death (Bern, 1994). As a result of such potential infections, the United States Public Health Service/Food and Drug Administration, divisions of the Department of Health and Human Services, have developed a policy or regulations with regard to milk quality. This model is known as the Pasteurized Milk Ordinance of 1978 (PMO), and contains the milk quality standards recommended to states, counties and municipalities. The following adoptions of these procedures by state legislatures, policy and standards by the individual states must be equal to be not lessor than those standards outlined in the PMO. States such as Florida and Illinois have their own divisions vested with the responsibility of policy making, licensing and inspecting of dairy farms and processing plants, and enforcement’s of individual Grade A milk programs.
Federal Agencies & Milk
The Food and Drug Administration (FDA) provides oversight for the processing of raw milk into pasteurized milk, cottage cheese, yogurt and sour cream under the National Conference on Intestate Milk Shipments “Grade A” milk program. This cooperative between the FDA and the 50 states including Puerto Rico helps to ensure the uniformity of milk regulations and the safety of milk and milk products (Bern, 1994). This program is also based on the PMO, and under the Grade A program, state personnel conduct inspections and assign ratings that are audited by FDA regional milk specialists. The FDA Grade A milk program includes pasteurized milk from cows, sheep, goats, and horses. Raw milk and raw milk cheeses cannot be labeled Grade A, since they are not pasteurized and not covered under the program (Berns, 1994).
Finally, the quality and safety processes for milk remains a concern for consumers, dairy farmers, and the government agencies that regulate milk and milk products. The world continues to grow, and the production of milk must continue to meet up to standards. According to the United Nations Population Division Report, the world population reached 6.1 billion in mid-2000 and is currently growing at an annual rate of 1.2%. Six of the poorest countries such as India, China, Pakistan, Nigeria, Bangladesh, and Indonesia, are responsible for half the observed growth. In 2050 the total world population is expected to be around 13 billion people, of which 11 billion will be in underdeveloped regions. The United Nations Food and Agricultural Organization estimates that world agricultural exports increased at an average annual rate of 3.2% in value terms from 1990 to 1999, with food exports growing at a rate of 3.7%. However, the agricultural trade of developing countries during this period represents only 50% of total world exports and it is concentrated in a minority of developing countries, a situation that creates an uneven trade balance in food from developed to developing countries.
The world’s milk production depends on agencies such as the FDA and national cooperation between dairy farms. Other suggestions for a comprehensive milk quality improvement system include the investigation of health status of raw milk, and the clear delineation of responsibilities for quality investigation, for activities and processes to improve milk quality. Processes such as pasteurization have created an extended shelf-life for milk and milk products. The government could also implement an extension service for milk producers, which would secure the necessary problem areas and would be aimed at obtaining the highest degree of efficiency and synergy. This service could include technical supervision, herd management, cow behavior, milking technique, animal health and hygiene and continuing education on milking techniques. Fortunately, the threat of milkborne diseases and the incidence of outbreaks involving milk and milk products has been greatly reduced over the decades due to improved sanitary milk production practices and pasteurization.
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