Information about Pasteurization

Pasteurization (or pasteurisation) is the process of heating liquids for the purpose of destroying viruses and harmful organisms such as bacteria, protozoa, molds, and yeasts. The process was named after its inventor, French scientist Louis Pasteur. The first pasteurization test was completed by Pasteur and Claude Bernard on April 20, 1862.

Unlike sterilization, pasteurization is not intended to kill all micro-organisms (pathogenic) in the food. Instead, pasteurization aims to achieve a "logarithmic reduction" in the number of viable organisms, reducing their number so they are unlikely to cause disease (assuming the pasteurized product is refrigerated and consumed before its expiration date). Commercial-scale sterilization of food is not common, because it adversely affects the taste and quality of the product.

Pasteurisation processes

Pasteurisation typically uses temperatures below boiling since at temperatures above the boiling point for milk casein micelles will irreversibly aggregate (or "curdle"). There are two main types of pasteurisation used today: high temperature/short time (HTST) and ultra-high temperature (UHT, Also known as Ultra-heat treated). In the HTST process, milk is forced between metal plates or through pipes heated on the outside by hot water, and is heated to 71.7 °C (161 °F) for 15-20 seconds. UHT processing holds the milk at a temperature of 138 °C (250 °F) for a fraction of a second. Milk simply labeled "pasteurized" is usually treated with the HTST method, whereas milk labeled "ultra-pasteurized" or simply "UHT" must be treated with the UHT method.

Pasteurisation methods are usually standardized and controlled by national food safety agencies (such as the USDA in the United States and the Food Standards Agency in the United Kingdom). These agencies require milk to be HTST pasteurized in order to qualify for the "pasteurized" label. There are different standards for different dairy products, depending on the fat content and the intended usage. For example, the pasteurisation standards for cream differ from the standards for fluid milk, and the standards for pasteurizing cheese are designed to preserve the phosphatase enzyme, which aids in cutting.

The HTST pasteurisation standard was designed to achieve a 5-log reduction (0.00001 times the original) in the number of viable microorganisms in milk. This is considered adequate for destroying almost all yeasts, mold, and common spoilage bacteria and also to ensure adequate destruction of common pathogenic heat-resistant organisms (including particularly Mycobacterium tuberculosis, which causes tuberculosis and Coxiella burnetii, which causes Q fever). HTST pasteurisation processes must be designed so that the milk is heated evenly, and no part of the milk is subject to a shorter time or a lower temperature.

Milk

Pasteurization is typically associated with milk, first suggested by Franz von Soxhlet in 1886. HTST pasteurized milk typically has a refrigerated shelf life of two to three weeks, whereas ultra pasteurized milk can last much longer when refrigerated, sometimes two to three months. When UHT pasteurization is combined with sterile handling and container technology, it can even be stored unrefrigerated for long periods of time.

Alternative milk pasteurization standards

In addition to the standard HTST and UHT pasteurization standards, there are other lesser-known pasteurization techniques. The first technique, called "batch pasteurization", involves heating large batches of milk to a lower temperature, typically 68 °C (145 °F) for 30 minutes, followed by quick cooling to about 4 °C (39 °F). The other technique is called higher-heat/shorter time (HHST), and it lies somewhere between HTST and UHT in terms of time and temperature. Pasteurization causes some irreversible and some temporary denaturation of the proteins in milk.

In 2001, the Animal and Plant Health Inspection Service of the USDA considered new rules requiring double pasteurization, which would have entailed holding milk at 72 °C (161 °F) for two separate 15-second periods, instead of one 30-second period as was the current standard. In most jurisdictions, milk treated by double pasteurization might not be considered pasteurized, depending on the temperature and duration of the heat treatment. Heat treatment might also be performed at a lower temperature or for a shorter time. Such milk could possibly be called "raw milk" or, confusingly, "unpasteurized milk". It cannot be called "pasteurized", even though a significant number of pathogens are destroyed during the process.

Some of the diseases that pasteurization can prevent are tuberculosis, diphtheria, polio, salmonellosis, strep throat, scarlet fever, and typhoid fever.

In fact, some doctors suggest that babies and breast-feeding mothers avoid all but UHT pasteurized dairy products.

In regions including Africa and South Asian countries, it is common to boil milk after it is harvested. This intense heating greatly changes the flavor of milk, which the respective people are accustomed to.

Are current milk pasteurization standards adequate?

Milk pasteurization has been subject to increasing scrutiny in recent years, due to the discovery of pathogens that are both widespread and heat resistant (able to survive pasteurization in significant numbers). Researchers have developed more sensitive diagnostics, such as real-time PCR and improved culture methods, that have enabled them to identify pathogens in pasteurized milk.

Recent developments

One bacterium in particular, the organism Mycobacterium avium subspecies paratuberculosis (MAP), which causes Johne's disease in cattle and is suspected of causing at least some Crohn's disease in humans, has been found to survive pasteurization in retail milk in the U.S., the UK, Greece, and the Czech Republic. The food safety authorities in the UK have decided to re-evaluate pasteurization standards in light of the MAP results and other evidence of harmful, pasteurization-resistant pathogens.

Some have argued that the United States Department of Agriculture (which is responsible for setting pasteurization standards) has not re-evaluated their position on adequate pasteurization. The organization does not dispute scientific studies showing danger as a result of MAP, but they maintain that the presence of MAP in retail pasteurized milk must be due to post-pasteurization contamination. However, some researchers within the Food and Drug Administration, which is responsible for food safety in the U.S., have begun pushing for a re-evaluation of these results. There is a small but growing body of criticism directed at these agencies by Crohn's disease sufferers, scientists, and doctors. Some have suggested that the U.S. dairy industry has been successful in suppressing the agencies' response to a potential health crisis, for fear of consumer panic which would lead to a decrease in milk consumption. It is worth noting that while MAP has not been definitely proven to be harmful in humans, all other mycobacteria are pathogenic, and it has been definitively shown to cause disease in cattle and other ruminants.

A newer method called flash pasteurization involves shorter exposure to higher temperatures, and is claimed to be better for preserving color and taste in some products.

The term cold pasteurization is used sometimes for the use of ionizing radiation (see Food irradiation) or other means (e.g. chemical) to kill bacteria in food. Food irradiation is also sometimes called "electronic pasteurization".

Controversy

In recent years, there has been growing consumer interest in raw (unpasteurized) milk products, due to potential health benefits. Advocates point out that many beneficial components of milk are destroyed by pasteurization. Specifically, raw milk contains immunoglobulins and the enzymes lipase and phosphatase, which are inactivated by heat. Raw milk contains vitamin B6, but the heat treatment may cause as much as 20% of the vitamin to be lost. Pasteurization also kills some of milk's naturally-occurring bacteria, such as Lactobacillus acidophilus, useful for the culturing of yogurt. Raw milk proponents point out that these "friendly" bacteria aid digestion and boost immunity.

Commercial distribution of packaged raw milk is prohibited in most countries. However, 28 US states allow sales of raw milk, and in other parts of the world, raw milk can often be bought direct from the farmer. In England, about 200 producers sell raw, or "green top" milk direct to consumers, either at the farm or through a delivery service. Raw milk is sometimes distributed through a share program, wherein the consumer owns a share in the dairy animal, and can be considered to be consuming milk from their own animal. In the United States, Arizona, California, and Washington allow raw milk sales in retail stores with appropriate warning labelling.

Drinking raw (untreated) milk or eating raw milk products is "like playing Russian roulette with your health," says John Sheehan, director of the Food and Drug Administration's Division of Dairy and Egg Safety. "We see a number of cases of food-borne illness every year related to the consumption of raw milk." [1]

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, according to the Centers for Disease Control and Prevention. [2]

Whether pasteurized or not, milk produced or stored in unsanitary conditions may harbor a host of disease-causing organisms (pathogens), such as the bacteria Campylobacter, Escherichia, Listeria, Salmonella, Yersinia, and Brucella. Common symptoms of food-borne illness from many of these types of bacteria include diarrhea, stomach cramps, fever, headache, vomiting, and exhaustion. The Weston Price Foundation notes that from 1982-1997 in the United States, over 238,000 people became ill from pathogens contracted by consuming properly pasteurized milk, including Campylobacter, Salmonella typhimurium, Listeria monocytogenes, E. coli, and Yersinia enterocolitica. [3]

Most healthy people recover from food-borne illness within a short period of time, but others may have symptoms that are chronic, severe, or life-threatening.

People with weakened immune systems, such as elderly people, children, and those with certain diseases or conditions, are most at risk for severe infections from pathogens that may be present in unsanitary milk. In pregnant women, Listeria monocytogenes-caused illness can result in miscarriage, fetal death, or illness or death of a newborn infant, and Escherichia coli infection has been linked to hemolytic uremic syndrome, a condition that can cause kidney failure and death. Raw milk advocates claim that the friendly bacteria in unpasteurized milk crowd out pathogens in the milk bottle the same way they do in the digestive system. Because pasteurization destroys these friendly bacteria, they say, pasteurized milk is an ideal growing medium for disease causing organisms.

Pasteurized products

Products that can be pasteurized :

• Apple cider
• Beer
• Canned food
• Crab
• Eggs
• Honey
• Juice
• Milk
• Sports drinks
• Water

See also

• Cold pasteurization
• Dairy product
• Flash pasteurization
• Homogenization
• Raw milk

External links

• A large collection of photographs from Dr. Robert Metcalf's solar water pasteurization projects in Africa
• Niro and GEA Liquid Processing information about pasteurization
• The Weston A. Price Foundation's website on the benefits of unpasteurized milk

References

• Rosenau, M.J., The Milk Question, Houghton Mifflin Company, Boston, 1913.