Pasteurization

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Cream pasteurising and cooling coils at Murgon Butter Factory, 1939

Pasteurisation or pasteurization is a process of heating food, which is usually a liquid, to a specific temperature for a predefined length of time and then immediately cooling it after it is removed from the heat. It is named after microbiologist Louis Pasteur for his work on his pasteurisation process. This process slows spoilage caused by microbial growth in the food.

Unlike sterilisation, pasteurisation is not intended to kill all micro-organisms in the food. Instead, it aims to reduce the number of viable pathogens so they are unlikely to cause disease (assuming the pasteurised product is stored as indicated and is 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 foods, such as dairy products, may be superheated to ensure pathogenic microbes are destroyed.[1]

Alcoholic beverages[edit]

The process of heating wine for preservation purposes has been known in China since 1117,[2] and was documented in Japan in 1900 in the diary Tamonin-nikki.

Much later, in 1768, an Italian priest and scientist Lazzaro Spallanzani proved experimentally that heat killed bacteria, and that they do not re-appear if the product is hermetically sealed.[3] In 1795, a Parisian chef and confectioner named Nicolas Appert began experimenting with ways to preserve foodstuffs, succeeding with soups, vegetables, juices, dairy products, jellies, jams, and syrups. He placed the food in glass jars, sealed them with cork and sealing wax and placed them in boiling water.[4] In that same year, the French military offered a cash prize of 12,000 francs for a new method to preserve food. After some 14 or 15 years of experimenting, Appert submitted his invention and won the prize in January 1810. Later that year,[5] Appert published L'Art de conserver les substances animales et végétales (or The Art of Preserving Animal and Vegetable Substances). This was the first cookbook of its kind on modern food preservation methods.[6][7]

La Maison Appert (English: The House of Appert), in the town of Massy, near Paris, became the first food-bottling factory in the world,[4] preserving a variety of food in sealed bottles. Appert's method was to fill thick, large-mouthed glass bottles with produce of every description, ranging from beef and fowl to eggs, milk and prepared dishes. His greatest success for publicity was an entire sheep. He left air space at the top of the bottle, and the cork would then be sealed firmly in the jar by using a vise. The bottle was then wrapped in canvas to protect it, while it was dunked into boiling water and then boiled for as much time as Appert deemed appropriate for cooking the contents thoroughly. Appert patented his method, sometimes called in his honor "appertisation".

Appert's method was so simple and workable that it quickly became widespread. In 1810, British inventor and merchant Peter Durand, also of French origin,[citation needed] patented his own method, but this time in a tin can, so creating the modern-day process of canning foods. In 1812, Englishmen Bryan Donkin and John Hall purchased both patents and began producing preserves. Just a decade later, Appert's method of canning had made its way to America.[8] Tin can production was however not common until the beginning of the 20th century, partly because a hammer and chisel were needed to open cans until the invention of a can opener by an Englishman named Yates in 1855.[4]

Appert's preservation by boiling involved heating the food to an unnecessarily high temperature, and for an unnecessarily long time, which could destroy some of the flavour of the preserved food.[citation needed]

A more timid method was developed by the renowned French chemist and microbiologist Louis Pasteur during his 1864[3] summer vacation in Arbois, to remedy the frequent acidity of the local wines. He found out experimentally that it is sufficient to heat a young wine to only about 50–60 °C (122–140 °F) for a brief time to kill the microbes, and that the wine could be nevertheless properly aged without sacrificing the final quality.[3] In honor of Pasteur, the process became known as "pasteurization".[citation needed] Pasteurization was originally used as a way of preventing wine and beer from souring,[9] and it would be many years before milk was pasteurized. In the United States in the 1870s, it was common for milk to contain contaminants to mask spoilage before milk was regulated.[10]

Milk[edit]

Milk is an excellent medium for microbial growth,[11] and when stored at ambient temperature bacteria and other pathogens soon proliferate.[12]

The Centers for Disease Control (CDC) says improperly handled raw milk is responsible for nearly three times more hospitalisations than any other food-borne disease outbreak, making it one of the world's most dangerous food products.[13] Diseases pasteurisation can prevent include tuberculosis, brucellosis, diphtheria, scarlet fever, and Q-fever; it also kills the harmful bacteria Salmonella, Listeria, Yersinia, Campylobacter, Staphylococcus aureus, and Escherichia coli O157:H7,[14][15] among others.

Pasteurisation is the 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-pasteurized 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 up to 9 months.

History[edit]

Before the widespread urban growth caused by industrialisation, people kept dairy cows even in urban areas and the short time period between production and consumption minimised the disease risk of drinking raw milk.[16] However, as urban densities increased and supply chains lengthened to the distance from country to city, raw milk (often days old) began to be recognised as a source of disease. For example, between 1912 and 1937 some 65,000 people died of tuberculosis contracted from consuming milk in England and Wales alone.[17]

Developed countries adopted milk pasteurization to prevent such disease and loss of life, and as a result milk is now widely considered one of the safest foods.[16] A traditional form of pasteurization by scalding and straining of cream to increase the keeping qualities of butter was practiced in England before 1773 and was introduced to Boston in the USA by 1773,[18] although it was not widely practiced in the United States for the next 20 years. It was still being referred to as a "new" process in American newspapers as late as 1802.[19] Pasteurization of milk was suggested by Franz von Soxhlet in 1886.[20]

Process[edit]

Pasteurization typically uses temperatures below boiling, since at very high temperatures, casein micelles will irreversibly aggregate, or "curdle". The two main types of pasteurization used today are high-temperature, short-time (HTST, also known as "flash") and extended shelf life (ESL). Ultra-high temperature processing (UHT, also known as ultra-heat-treating) 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 72°C (161°F) for 15 seconds.[21]:8 UHT processing holds the milk at a temperature of 138°C (280°F) for a minimum of two seconds.[21]:90 ESL milk has a microbial filtration step and lower temperatures than UHT milk.[22] Milk simply labeled "pasteurized" is usually treated with the HTST method, whereas milk labeled "ultra-pasteurized" or simply "UHT" has been treated with the UHT method. Since 2007, however, it is no longer a legal requirement in European countries (for example in Germany) to declare ESL milk as ultra-heated; consequently, it is now often labeled as "fresh milk" and just advertised as having an "extended shelf life", making it increasingly difficult to distinguish ESL milk from traditionally pasteurized fresh milk. A less conventional, but US FDA-legal, alternative (typically for home pasteurization) is to heat milk at 145 °F (63 °C) for 30 minutes.[23]

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 that milk be HTST pasteurized to qualify for the pasteurized label. Dairy product standards differ, depending on fat content and intended usage. For example, pasteurization standards for cream differ from standards for fluid milk, and standards for pasteurizing cheese are designed to preserve the enzyme phosphatase, which aids cutting. In Canada, all milk produced at a processor and intended for consumption must be pasteurized, which legally requires that it be heated to at least 72°C for at least 16 seconds,[24] then cooling it to 4°C to ensure any harmful bacteria are destroyed. The UK Dairy Products Hygiene Regulations 1995 requires that milk be heat treated for 15 seconds at 71.7 °C or other effective time/temperature combination.[25]

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.[23]

Efficacy[edit]

The HTST pasteurization standard was designed to achieve a five-log reduction, killing 99.999% of the number of viable micro-organisms in milk.[26] This is considered adequate for destroying almost all yeasts, molds, 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).[26] As a precaution, modern equipment tests and identifies bacteria in milk being processed. HTST pasteurization processes must be designed so the milk is heated evenly, and no part of the milk is subject to a shorter time or a lower temperature.

Even pasteurization without quality control can be effective, though this is generally not permitted for human consumption; a study of farms feeding calves on pasteurised waste milk using a mixture of pasteurization technologies (none of which were routinely monitored for performance) found the resulting pasteurized milk to meet safety requirements at least 92% of the time.[27]

An effect of the heating of pasteurization is that some vitamin, mineral, and beneficial (or probiotic) bacteria is lost. Soluble calcium and phosphorus decrease by 5%, thiamin and vitamin B12 by 10%, and vitamin C by 20%.[17][28] However, these losses are not significant nutritionally. [29]

Verification[edit]

Direct microbiological techniques are the ultimate measurement of pathogen contamination but these are costly and time consuming (24-48 hours), which means that products are able to spoil by the time pasteurisation is verified.

As a result of the unsuitability of microbiological techniques, milk pasteurisation efficacy is typically monitored by checking for the presence of alkaline phosphatase, which is denatured by pasteurisation. B. tuberculosis, the bacterium requiring the highest temperature to be killed of all milk pathogens is killed at similar ranges of temperature and time as those which denature alkaline phosphatase. For this reason, presence of alkaline phosphatase is deemed to be an ideal diagnostic tool for pasteurisation efficacy.[30][31]

Phosphatase denaturing was originally monitored using a phenol-phosphate substrate. When hydrolysed by the enzyme these compounds liberate phenols, which were then reacted with dibromoquinonechlorimide to give a colour change, which itself was measured by checking absorption at 610 nm (spectrophotometry). Some of the phenols used were inherently coloured (phenolpthalein, nitrophenol) and were simply assayed unreacted.[25] Spectophotometric analysis is satisfactory but is of relatively low accuracy because many natural products are coloured. For this reason, modern systems (since 1990) use fluorometry which is able to detect much lower levels of raw milk contamination.[25]

Unpasteurised milk[edit]

According to the Centers for Disease Control between 1998 and 2011 79% of the dairy related outbreaks were due to raw milk or cheese products.[32] They report 148 outbreaks, 2,384 illnesses (284 requiring hospitalizations) as well as 2 deaths due to raw milk or cheese products during the same time period.[32]

Consumer acceptance[edit]

As pasteurisation is a very old and traditional way of preservation, it is well known and accepted by consumers. Nearly every label of milk products contains the word "pasteurisation" and it is associated by consumers with good quality attributes and safety. In the consumer studies of Hightech Europe consumers mentioned more positive than negative associations for this technology showing that these products are well accepted.[33]

Products that are commonly pasteurised[edit]

See also[edit]

References[edit]

  1. ^ Montville, T. J., and K. R. Matthews: "food microbiology an introduction", page 30. American Society for Microbiology Press, 2005.
  2. ^ Hornsey, Ian Spencer and George Bacon (2003). A History of Beer and Brewing. Royal Society of Chemistry. p. 30. ISBN 0-85404-630-5. "[…] sake is pasteurized and it is interesting to note that a pasteurization technique was first mentioned in 1568 in the _Tamonin-nikki_, the diary of a Buddhist monk, indicating that it was practiced in Japan some 300 years before Pasteur. In China, the first country in East Asia to develop a form of pasteurization, the earliest record of the process is said to date from 1117." 
  3. ^ a b c Vallery-Radot, René (2003-03-01). Life of Pasteur 1928. pp. 113–114. ISBN 978-0-7661-4352-4. 
  4. ^ a b c Lance Day, Ian McNeil, ed. (1996). Biographical Dictionary of the History of Technology. Routledge. ISBN 0-415-19399-0. 
  5. ^ Gordon L. Robertson (1998). Food Packaging: Principles End Practice. Marcel Dekker. p. 187. ISBN 978-0-8247-0175-8. 
  6. ^ "''The First Book on Modern Food Preservation Methods (1810)''". Historyofscience.com. 2009-09-29. Retrieved 2014-03-19. 
  7. ^ Wiley, R. C (1994). Minimally processed refrigerated fruits and vegetables. p. 66. ISBN 978-0-412-05571-3. "Nicolas Appert in 1810 was probably the first person […]" 
  8. ^ Alvin Toffler, "Future Shock".
  9. ^ Carlisle, Rodney (2004). Scientific American Inventions and Discoveries, p.357. John Wiley & Songs, Inc., new Jersey. ISBN 0-471-24410-4.
  10. ^ Hwang, Andy; Huang, Lihan (31 January 2009). Ready-to-Eat Foods: Microbial Concerns and Control Measures. CRC Press. p. 88. ISBN 978-1-4200-6862-7. Retrieved 19 April 2011. 
  11. ^ "Harold Eddleman, ''Making Milk Media'', Indiana Biolab". Disknet.com. Retrieved 2014-03-19. 
  12. ^ "Frank O'Mahony, ''Rural dairy technology: Experiences in Ethiopia'', International Livestock Centre for Africa". Ilri.org. Retrieved 2014-03-19. 
  13. ^ "Food safety of raw milk". Foodsmart.govt.nz. Retrieved 2014-03-19. 
  14. ^ "Milk Pasteurization: Guarding against disease", Michigan State University Extension
  15. ^ Smith, P. W., (August 1981), "Milk Pasteurization" Fact Sheet Number 57, U.S. Department of Agriculture Research Service, Washington, D.C.
  16. ^ a b Hotchkiss, Joseph H. (2001), "Lambasting Louis: Lessons from Pasteurization", National Agricultural Biotechnology Council Report 13: 61 
  17. ^ a b Wilson, G. S. (1943), "The Pasteurization of Milk", British Medical Journal 1 (4286): 261 
  18. ^ News article, [Boston] Independent Ledger, 16 June 1783
  19. ^ News article, Western Constellation, 19 July 1802
  20. ^ 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.
  21. ^ a b "Grade A Pasteurized Milk Ordinance 2009 Revision". US Department of Health and Human Services. 
  22. ^ Koel, Jaan (2001). "Paving the Way for ESL". Dairy Foods. 
  23. ^ a b Rich, Robert (5 September 2003). "Keeping it raw". The Mountain View Voice (Embarcadero Publishing Company). Retrieved 23 October 2010. 
  24. ^ Canadian Food Inspection System – Dairy Production and Processing Regulations (Fourth Edition) – 2005[dead link]
  25. ^ a b c Langridge, E W. The Determination of Phosphatase Activity. Quality Management Ltd. Retrieved 2013-12-20. 
  26. ^ a b Stabel, J. R.; Lambertz, A. (2004), "Efficacy of Pasteurization Conditions for the Inactivation of Mycobacterium avium subsp. paratuberculosis in Milk", Journal of Food Protection 67 (12): 2719 
  27. ^ "Penn State Study Finds Calf Milk Pasteurization Effective, but Variable — Dairy — Penn State Extension". Extension.psu.edu. 2010-12-14. Retrieved 2014-03-19. 
  28. ^ Krauss, W. E., Erb, J. H. and Washburn, R.G., "Studies on the nutritive value of milk, II. The effect of pasteurization on some of the nutritive properties of milk," Ohio Agricultural Experiment Station Bulletin 518, page 30, January, 1933.
  29. ^ Claeys, Wendy L.; Sabine Cardoen, Georges Daube, Jan De Block, Koen Dewettinck, Katelijne Dierick, Lieven De Zutter, André Huyghebaert, Hein Imberechts, Pierre Thiange, Yvan Vandenplas, Lieve Herman (May 2013). "Raw or heated cow milk consumption: Review of risks and benefits". Food Control 31 (1): 251–262. doi:10.1016/j.foodcont.2012.09.035. 
  30. ^ Kay, H. (1935). "Some Results of the Application of a Simple Test for Efficiency of Pasteurisation". The Lancet 225 (5835): 1516–1518. doi:10.1016/S0140-6736(01)12532-8.  edit
  31. ^ Hoy, W. A.; Neave, F. K. (1937). "The Phosphatase Test for Efficient Pasteurisation". The Lancet 230 (5949): 595. doi:10.1016/S0140-6736(00)83378-4.  edit
  32. ^ a b "CDC - Raw Milk Questions and Answers - Food Safety". Cdc.gov. 2014-03-07. Retrieved 2014-03-19. 
  33. ^ "Documents". Hightecheurope.eu. Retrieved 2014-03-19. 

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