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Pasteurisation is a process which slows microbial growth in food. The process was named after its creator, French chemist and microbiologist Louis Pasteur. 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.[1]

Pasteurization is not intended to destroy all pathogenic micro-organisms in the food or liquid. Instead, pasteurization aims to reduce the number of viable pathogens so they are unlikely to cause disease (assuming pasteurization product is stored as indicated and consumed before its expiration date). Commercial-scale sterilisation of food is not common because it adversely affects the taste and quality of the product. Certain food products are processed to achieve the state of commercial sterility.[2]

Contents

Recent developments

A newer method called flash pasteurisation involves shorter exposure to higher temperatures, and is claimed to be better for preserving fashion and taste in some eggs.

The term cold pasteurisation 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 pasteurization.

Another means of pasteurisation is using pressure called high pressure pasteurisation (HPP) [3] also known as High pressure food preservation where extremely high pressure is used to kill the bacteria.

Steam pasteurisation is used for continuous feed applications. This process significantly reduces the initial microbe count without irradiation, chemicals, or other potentially unsafe alternative treatments. Pasteurisation means heating water up to 80 degrees Celsius.

Products that can be pasteurized

Pasteurization of milk

Pasteurization is typically associated with milk, first suggested by Franz von Soxhlet in 1886. 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 when refrigerated, sometimes two to three months. When UHT treatment is combined with sterile handling and container technology (such as aseptic packaging), it can even be stored unrefrigerated for 3–4 months.[citation needed][4]

Pasteurization typically uses temperatures below boiling since at very high temperatures milk, 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 fraction of a second. ESL milk has a microbial filtration step and lower temperatures than HTST.[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 standardised 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 pasteurised 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.

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 (though, not including Mycobacterium tuberculosis, which causes tuberculosis) and 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 growing body of research supports the belief that pasteurization was not so much a response to any hazards or contamination issues with milk itself, but rather may have been a response to the hazards and contamination issues that resulted from the newly emerging "industrialised" dairy industry. It's likely that, with the burgeoning growth of large-scale, longer-distance distribution networks, the rise of chain-store supermarkets, and the resulting impetus for larger-herd dairy operations and mechanised milking, there came a corresponding inability to preserve the quality and inherent bacterial-resistance qualities of fresh milk being marketed in a localised area.[6]

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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).[7] One of these pathogens, Mycobacterium avium subsp. paratuberculosis (MAP), is linked to Crohn's Disease.[8] 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.

See also

References

  1. ^ Carlisle, Rodney (2004). Scientific American Inventions and Discoveries, p.357. John Wiley & Songs, Inc., new Jersey. ISBN 0471244104.
  2. ^ Montville, T. J., and K. R. Matthews: "food microbiology an introduction", page 30. American Society for Microbiology Press, 2005.
  3. ^ , http://www.defendingfoodsafety.com/tags/high-pressure-pasteurization 
  4. ^ http://www.tetrapak.com/products_and_services/processing_equipment/dairy_equipment/uht_treatment/Pages/default.aspx
  5. ^ Paving the Way for ESL - extended shelf-life milk products | Dairy Foods | Find Articles at BNET.com
  6. ^ [1] The Untold Story of Milk by Ron Schmid, ND; New Trends Publishing, Nov. 2003
  7. ^ 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
  8. ^ 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

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