Pasteurized Milk
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Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food. The process of heating wine to preserve it longer was known in China since AD.1117,[1] and is documented in Japan in 1568 in the diary Tamonin-nikki, but the modern version was created by the French chemist and microbiologist Louis Pasteur, after whom it is named. The first pasteurization test was completed by Louis Pasteur and Claude Bernard on April 20, 1864. The process was originally conceived as a way of preventing wine and beer from souring.[2]

Unlike sterilization, pasteurization is not intended to kill all micro-organisms in the food. Instead pasteurization aims to reduce the number of viable pathogens so they are unlikely to cause disease (assuming the pasteurized product is stored as indicated 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. Certain food products, like dairy products, are superheated to ensure pathogenic microbes are destroyed.[3]

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[edit] Pasteurization of milk

Pasteurization is typically associated with milk; pasteurization of milk was first suggested by Franz von Soxhlet in 1886.[4] It is the main reason for milk's extended shelf life. High Temperature Short Time (HTST) pasteurised milk typically has a refrigerated shelf life of two to three weeks, whereas ultra pasteurised milk can last much longer, sometimes two to three months. When ultra heat treatment (UHT) is combined with sterile handling and container technology (such as aseptic packaging), it can even be stored unrefrigerated for 6–9 months

Pasteurization typically uses temperatures below boiling since at very high temperatures casein micelles will irreversibly aggregate, or "curdle." There are two main types of pasteurization used today: High Temperature/Short Time (HTST) and "Extended Shelf Life (ESL)" treatment. Ultra-high temperature (UHT or ultra-heat treated) is also used for milk treatment. 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 135 °C (275 °F) for a minimum of one second. ESL milk has a microbial filtration step and lower temperatures than UHT.[5] Milk simply labeled "pasteurised" is usually treated with the HTST method, whereas milk labeled "ultra-pasteurised" or simply "UHT" has been treated with the UHT method.

Pasteurization 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 "pasteurization" label. There are different standards for different dairy products, depending on the fat content and the intended usage. For example, the pasteurization 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.

In Canada, all milk produced at a processor and intended for consumption must be pasteurized, legally requiring it to be heated to at least 72 degrees Celsius for at least 16 seconds[6] and then cooling it to 4 degrees Celsius. This ensures that any harmful bacteria are destroyed.

The HTST pasteurization standard was designed to achieve a 5-log reduction, killing 99.999% of the number of viable micro-organisms 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 Mycobacterium tuberculosis, which causes tuberculosis but not Coxiella burnetii, which causes Q fever). HTST pasteurization 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.

A process similar to pasteurization is thermization, which uses lower temperatures to kill bacteria in milk. It allows a milk product, such as cheese, to retain more of the original taste, but thermized foods are not considered pasteurized by food regulators.[7]

[edit] Effectiveness of pasteurization

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).[8] One of these pathogens, Mycobacterium avium subsp. paratuberculosis (MAP), is linked to Crohn's Disease.[9][verification needed] Researchers have developed more sensitive diagnostics, such as real-time PCR and improved culture methods that have enabled them to identify pathogens in pasteurised milk.

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

Further information: United States raw milk debate

[edit] Products that are commonly pasteurized

[edit] See also

[edit] References

  1. ^ Hornsey, Ian Spencer (2003). A History of Beer and Brewing. Royal Society of Chemistry. ISBN 0854046305. http://www.cse.iitk.ac.in/users/amit/books/hornsey-2003-history-of-beer.html.  on p.30: ... sake is pasteurised and it is interesting to note that a pasteurisation technique was first mentioned in 1568 in the _Tamonin-nikki_, the diary of a Buddhist monk, indicating that it was practised in Japan some 300 years before Pasteur. In China, the first country in East Asia to develop anything resembling pasteurisation, the earliest record of the process as said to date from 1117.
  2. ^ Carlisle, Rodney (2004). Scientific American Inventions and Discoveries, p.357. John Wiley & Songs, Inc., new Jersey. ISBN 0471244104.
  3. ^ Montville, T. J., and K. R. Matthews: "food microbiology an introduction", page 30. American Society for Microbiology Press, 2005.
  4. ^ Franz Soxhlet (1886) "Über Kindermilch und Säuglings-Ernährung" (On milk for babies and infant nutrition), Münchener medizinische Wochenschrift (Munich Medical Weekly), vol. 33, pages 253, 276.
  5. ^ Paving the Way for ESL - extended shelf-life milk products | Dairy Foods | Find Articles at BNET.com
  6. ^ Canadian Food Inspection System - Dairy Production and Processing Regulations (Fourth Edition) - 2005
  7. ^ Rich, Robert (September 5, 2003). "Keeping it raw". The Mountain View Voice (Embarcadero Publishing Company). http://www.mv-voice.com/morgue/2003/2003_09_05.dinea.html. Retrieved October 23, 2010. 
  8. ^ Irene R. Grant et al., "Effect of Commercial-Scale High-Temperature, Short-Time Pasteurization on the Viability of Mycobacterium paratuberculosis in Naturally Infected Cows' Milk", Applied and Environmental Microbiology, February 2002, p. 602-607, Vol. 68, No. 2
  9. ^ F. Autschbach, S. Eisold, U. Hinz, S. Zinser et al., "High prevalence of Mycobacterium avium subspecies paratuberculosis IS900 DNA in gut tissues from individuals with Crohn’s disease", July, 2005, p. 944-949 , Vol. 54

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Pasteurization"