Volume 82, Number 1 January/February 2011
Microbiological Contaminants. Contamination by bacteria is considered to be the most serious food safety issue (1,2,8). Because of the nutrient rich composition of milk and milk products, these foods are a good medium for the survival and growth of a variety of pathogenic bacteria (6e,7,9). However, as a result of improved animal health and management, plant sanitation, and widespread use of pasteurization, the incidence of milkborne illness in the U.S. has decreased from approximately 25% of all reported foodborne illness outbreaks in 1938 to less than 1% of reported outbreaks in 2009 (5).
Pasteurization is described as “the process of heating every particle of milk or milk product, in properly designed and operated equipment” to one of several temperatures for a corresponding specified time as defined in the PMO, most commonly to at least 161° F for at least 15 seconds followed by rapid cooling to 40° F (5). Alternatively, some milk and milk products can be ultra-pasteurized, which involves heating milk to 280° F for at least 2 seconds, or sterilized at an ultra-high temperature (i.e., 280° F to 302° F for at least 2 seconds) (5,6d,7). Ultra-pasteurized milk has an extended shelf-life under refrigerated conditions (5), whereas milk products heated to an ultra-high temperature and aseptically packaged may be stored at room temperature for at least six months (6d).Pasteurization of raw milk is recognized worldwide as an essential public health measure to reduce the risk of illnesses from pathogenic bacteria and increase the shelf life of milk and milk products.
Proper pasteurization destroys pathogenic bacteria, yeast, and molds that may be associated with raw milk, as well as increases the product’s shelf life (5,7). Milk pasteurization is recommended for all milk consumed by humans by the Centers for Disease Control (10), the FDA (11), the 2005 Dietary Guidelines (8), and the 2010 Dietary Guidelines Advisory Committee (4), among other medical and scientific organizations identified in a recent review article (7).
Although some people believe that raw milk, either conventionally or organically produced, is a healthier alternative to pasteurized milk, there is little or no impact of pasteurization on the nutritional quality of milk or on milk’s natural, antimicrobial properties (7,11-13). The majority of milkborne illnesses are associated with the consumption of raw (unpasteurized) milk and milk products (6e). Between 1998 and 2008, 85 outbreaks of human infections resulting from consumption of raw milk were reported to the Centers for Disease Control (9,14). These outbreaks included more than 1,600 illnesses, 187 hospitalizations, and two deaths. The actual number of illnesses associated with raw milk likely exceeds this number given that not all foodborne illnesses are recognized and reported. Several pathogenic microorganisms may be found in raw milk including Campylobacter jejuni, Salmonella spp., Listeria monocytogenes, Yersinia enterocolitica, Escherichia coli, and Staphylococcus aureus (4,6e,7,10). Milkborne pathogens can affect the health of anyone who drinks raw milk; however, they are especially dangerous for high-risk consumers such as pregnant women, children, the elderly, and people with weakened immune systems (6e,8,15).
Pasteurization is required by law for all Grade “A” fluid milk and milk products moved in interstate commerce for retail sale (5). Also, U.S. Standards of Identity for cheese products require pasteurization for certain natural cheeses (i.e., fresh or soft-ripened cheeses) (16). Most cheese made in the U.S. is manufactured using pasteurized milk (6g). However, some hard and semi-hard cheeses can be made with raw milk (6e). To U.S. pasteurized milk and milk products are among the safest foods marketed nationwide. This success is attributed in large part to compliance with strict food safety regulations and adoption of proactive measures from farm to fridge. ensure their safety, cheeses made from raw milk must be aged for at least 60 days at not less than 35° F (6e). While the majority of states currently allow raw milk sales within their borders with certain limitations (6e), a number of regulatory, medical, educational, and public health authorities identified in a recent review article have published position statements supporting restriction of raw milk and milk products (7).
Chemical Contaminants. Risk of adverse health effects from chemical contaminants such as antibiotics and pesticide residues in milk and other dairy foods is minimal, or non-existent, because of stringent regulations and programs from the farm to the marketplace. Antibiotics, primarily penicillin and tetracycline, may be given to dairy cows in therapeutic doses to treat temporary bacterial infections such as mastitis (5). Before approved for use, these antibiotics must meet extensive pre-clearance requirements (5,17). Federal law requires dairy farmers to wait a specified withdrawal time, usually 72 to 96 hours, after administering antibiotics to dairy cows to ensure that the antibiotics have cleared the cow’s system and that the milk is safe to consume. In establishing withdrawal times, the FDA applies wide margins of safety to ensure food safety (17).
The PMO requires that milk (both conventionally and organically produced) in all bulk milk tankers arriving at a dairy plant be sampled and analyzed for animal drug residues before milk is unloaded and processed (5). State regulatory agencies monitor the industry’s surveillance activities by routinely making unannounced on-site inspections to collect milk samples for antibiotic residues and review industry records (5). According to FDA’s most recent (2008) National Milk Drug Residue Data Base, which is a voluntary industry reporting program, only 0.028% of over three million tanker loads of raw milk from dairy farms and only 0.007% of 43,940 pasteurized fluid milk and milk products analyzed were positive for any animal drug residue (i.e., antibiotics) (18). In those rare cases when a tanker load of milk tests positive, the entire load of milk is rejected and the milk does not reach the consumer.
Pesticide residues are not a health concern in any U.S. milk products as a result of industry preventive programs and federal regulations which limit exposure to these contaminants (19,20). All pesticides sold in the U.S. must be approved for safety by the Environmental Protection Agency before being used (19). Regulatory agencies have also set tolerance or threshold levels for allowable pesticide residues in foods such as milk (20). Because pesticides are found in water and soil, extremely low levels can be found in all foods, conventional and organic. The FDA, under its pesticide monitoring program, collects and samples food nationwide for pesticide and other chemical contaminants (21). This surveillance has shown that pesticide contamination of foods in the U.S. is extremely low. For example, no samples of domestic dairy products tested in Fiscal Year 2008 contained levels of pesticide residues above well-established thresholds (21). Foods shown to contain levels of chemical residues above the maximum allowable levels are removed from the marketplace (21).
Hormones. Some people perceive hormones as a food safety concern (2). All cows have the natural protein hormone bovine somatotropin (bst) that helps them produce milk. Some dairy farmers may use the FDA-approved synthetic hormone, recombinant bovine somatotropin (rbST), in lactating cows to increase milk yield, improve the milk-to-feed ratio, and decrease waste (22). This synthetic hormone is not added to milk and the composition of milk from treated and untreated cows is the same (23). Based on a recent review of the scientific evidence, the FDA states that milk from cows treated with rbST is safe for human consumption (24).
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