Editing Pasteurization (section)

==Pasteurization process==

[[File:Simple Pasteurization.png|thumb|General overview of the pasteurization process. The milk starts at the left and enters the piping with functioning enzymes that, when heat-treated, become denatured and stop functioning. This prevents pathogen growth by stopping the functionality of the cell. The cooling process helps stop the milk from undergoing the [[Maillard reaction]] and caramelization.]]
Pasteurization is a mild heat treatment of liquid foods (both packaged and unpackaged) where products are typically heated to below {{convert|100|C|F}}. The heat treatment and cooling process are designed to inhibit a phase change in the product. The [[acidity]] of the food determines the parameters (time and temperature) of the heat treatment as well as the duration of shelf life. Parameters also take into account nutritional and sensory qualities that are sensitive to heat.

In acidic foods (with [[pH]] of 4.6 or less), such as fruit juice and [[beer]], the heat treatments are designed to inactivate enzymes (pectin [[Protein-glutamate methylesterase|methylesterase]] and [[polygalacturonase]] in fruit juices) and destroy spoilage microbes (yeast and [[lactobacillus]]). Due to the low pH of acidic foods, pathogens cannot grow. The shelf-life is thereby extended by several weeks. In less acidic foods (with pH greater than 4.6), such as milk and liquid eggs, heat treatments are designed to destroy pathogens and spoilage organisms (yeast and molds). Not all spoilage organisms are destroyed under pasteurization parameters, so subsequent refrigeration is necessary.<ref name="Fellows-2017"/>

High-temperature short-time (HTST) pasteurization, such as that used for milk ({{convert|71.5|C|F}} for 15 seconds) ensures the safety of milk and provides a refrigerated shelf life of approximately two weeks. In ultra-high-temperature (UHT) pasteurization, milk is pasteurized at {{convert|135|C|F}} for 1–2 seconds, which provides the same level of safety, but along with the packaging, extends shelf life to three months under refrigeration.<ref>{{Cite journal|last1=Chavan|first1=Rupesh S.|last2=Chavan|first2=Shraddha Rupesh|last3=Khedkar|first3=Chandrashekar D.|last4=Jana|first4=Atanu H.|date=2011-08-22|title=UHT Milk Processing and Effect of Plasmin Activity on Shelf Life: A Review|journal=Comprehensive Reviews in Food Science and Food Safety|language=en|volume=10|issue=5|pages=251–68|doi=10.1111/j.1541-4337.2011.00157.x|issn=1541-4337}}</ref>

===Equipment===

Food can be pasteurized either before or after being packaged into containers. Pasteurization of food in containers generally uses either steam or hot water. When food is packaged in glass, hot water is used to avoid cracking the glass from [[thermal shock]]. When plastic or metal packaging is used, the risk of thermal shock is low, so steam or hot water is used.<ref name="Fellows-2017"/>

Most liquid foods are pasteurized by using a continuous process that passes the food through a heating zone, a hold tube to keep it at the pasteurization temperature for the desired time, and a cooling zone, after which the product is filled into the package. [[Plate heat exchanger]]s are often used for low-[[viscosity]] products such as animal milk, nut milk, and juices. A plate heat exchanger is composed of many thin vertical stainless steel plates that separate the liquid from the heating or cooling medium. 

[[Shell and tube heat exchanger|Shell and tube heat exchangers]] are often used for the pasteurization of foods that are [[non-Newtonian fluid]]s, such as dairy products, tomato [[ketchup]], and baby foods. A tube heat exchanger is made up of concentric stainless steel tubes. Food passes through the inner tube or tubes, while the heating/cooling medium is circulated through the outer tube.

Scraped-surface heat exchangers are a type of shell and tube that contain an inner rotating shaft having spring-loaded blades that serve to scrape away any highly viscous material that accumulates on the wall of the tube.<ref>{{Cite book|title=Introduction to Food Process Engineering|last=Smith|first=P. G|publisher=Food Science Text Series|year=2003|pages=152–54, 259–50}}</ref>

The benefits of using a [[heat exchanger]] to pasteurize foods before packaging, versus pasteurizing foods in containers are:
* Higher uniformity of treatment
* Greater flexibility with regard to the products that can be pasteurized
* Higher heat transfer-efficiency<ref name="Fellows-2017"/>
* Greater throughput with many other processes of using the milk 


After being heated in a heat exchanger, the product flows through a hold tube for a set period to achieve the required treatment. If pasteurization temperature or time is not achieved, a flow diversion valve is used to divert the under-processed product back to the raw product tank.<ref>{{Cite journal|date=2005-06-01|title=HACCP with multivariate process monitoring and fault diagnosis techniques: application to a food pasteurization process|journal=Food Control|language=en|volume=16|issue=5|pages=411–422|doi=10.1016/j.foodcont.2004.04.008|issn=0956-7135|last1=(Kosebalaban) Tokatli|first1=Figen|last2=Cinar|first2=Ali|last3=Schlesser|first3=Joseph E.|hdl=11147/1960|hdl-access=free}}</ref> If the product is adequately processed, it is cooled in a heat exchanger, then filled.

===Verification===

Direct microbiological techniques are the ultimate measurement of pathogen contamination, but these are costly and time-consuming, which means that products have a reduced shelf-life by the time pasteurization is verified.

As a result of the unsuitability of microbiological techniques, milk pasteurization efficacy is typically monitored by checking for the presence of [[alkaline phosphatase]], which is denatured by pasteurization. Destruction of alkaline phosphatase ensures the destruction of common milk pathogens. Therefore, the presence of alkaline phosphatase is an ideal indicator of pasteurization efficacy.<ref>{{Cite journal|last1=Kay|first1=H.|year=1935|title=Some Results of the Application of a Simple Test for Efficiency of Pasteurization|journal=The Lancet|volume=225|issue=5835|pages=1516–18|doi=10.1016/S0140-6736(01)12532-8}}</ref><ref>{{Cite journal|last1=Hoy|first1=W.A.|last2=Neave|first2=F.K.|year=1937|title=The Phosphatase Test for Efficient Pasteurization|journal=The Lancet|volume=230|issue=5949|pages=595|doi=10.1016/S0140-6736(00)83378-4}}</ref> For [[Breaker eggs|liquid eggs]], the effectiveness of the heat treatment is measured by the residual activity of [[Alpha-amylase|α-amylase]].<ref name="Fellows-2017"/>

====Efficacy against pathogenic bacteria====

During the early 20th century, there was no robust knowledge of what time and temperature combinations would inactivate pathogenic bacteria in milk, so several different pasteurization standards were in use. By 1943, both HTST pasteurization conditions of {{convert|72|C|F}} for 15 seconds, as well as batch pasteurization conditions of {{convert|63|C|F}} for 30 minutes, were confirmed by studies of the complete thermal death (as best as could be measured at that time) for a range of pathogenic bacteria in milk.<ref>{{Cite journal|last=Ball|first=C. Olin|date=1943-01-01|title=Short-Time Pasteurization of Milk|journal=Industrial & Engineering Chemistry|volume=35|issue=1|pages=71–84|doi=10.1021/ie50397a017|issn=0019-7866}}</ref> Complete inactivation of ''[[Coxiella burnetii]]'' (which was thought at the time to cause [[Q fever]] by oral ingestion of infected milk)<ref>{{Cite journal|last1=Enright|first1=J.B.|last2=Sadler|first2=W.W.|last3=Thomas|first3=R.C.|date=1957|title=Thermal inactivation of Coxiella burnetii and its relation to pasteurization of milk|journal=Public Health Monograph|volume=47|pages=1–30|issn=0079-7596|pmid=13465932}}</ref><ref>{{Cite journal|last1=Cerf|first1=O.|last2=Condron|first2=R.|date=2006|title=Coxiella burnetii and milk pasteurization: an early application of the precautionary principle?|journal=Epidemiology & Infection|volume=134|issue=5|pages=946–51|doi=10.1017/S0950268806005978|issn=1469-4409|pmc=2870484|pmid=16492321}}</ref> as well as of ''[[Mycobacterium tuberculosis]]'' (which causes [[tuberculosis]])<ref>{{Cite journal|last1=Kells|first1=H.R.|last2=Lear|first2=S.A.|date=1960-07-01|title=Thermal Death Time Curve of Mycobacterium tuberculosis var. bovis in Artificially Infected Milk|url= |journal=Applied Microbiology|language=en|volume=8|issue=4|pages=234–236|doi=10.1128/am.8.4.234-236.1960|issn=0099-2240|pmc=1057612|pmid=14405283}}</ref> were later demonstrated. For all practical purposes, these conditions were adequate for destroying almost all [[yeast]]s, [[Mold (fungus)|mold]]s, and common [[Food spoilage|spoilage]] bacteria and also for ensuring adequate destruction of common pathogenic, heat-resistant organisms. However, the microbiological techniques used until the 1960s did not allow for the actual reduction of bacteria to be enumerated. Demonstration of the extent of inactivation of pathogenic bacteria by milk pasteurization came from a study of surviving bacteria in milk that was heat-treated after being deliberately spiked with high levels of the most heat-resistant strains of the most significant milk-borne pathogens.<ref name="Pearce-2012">{{Cite journal|last1=Pearce|first1=L.E.|last2=Smythe|first2=B.W.|last3=Crawford|first3=R.A.|last4=Oakley|first4=E.|last5=Hathaway|first5=S.C.|last6=Shepherd|first6=J.M.|date=2012|title=Pasteurization of milk: The heat inactivation kinetics of milk-borne dairy pathogens under commercial-type conditions of turbulent flow|url=http://www.journalofdairyscience.org/article/S0022-0302(11)00673-4/abstract|journal=Journal of Dairy Science|language=en|volume=95|issue=1|pages=20–35|doi=10.3168/jds.2011-4556|issn=0022-0302|pmid=22192181|doi-access=free|access-date=15 June 2017|archive-date=19 July 2022|archive-url=https://web.archive.org/web/20220719140721/https://www.journalofdairyscience.org/article/S0022-0302%2811%2900673-4/fulltext|url-status=live}}</ref>

The mean log<sub>10</sub> reductions and temperatures of inactivation of the major milk-borne pathogens during a 15-second treatment are:
* ''[[Staphylococcus aureus]]'' >&nbsp;6.7 at {{convert|66.5|C|F}}
* ''[[Yersinia enterocolitica]]'' >&nbsp;6.8 at {{convert|62.5|C|F}}
* Pathogenic ''[[Escherichia coli]]'' >&nbsp;6.8 at {{convert|65|C|F}}
* ''[[Cronobacter sakazakii]]'' >&nbsp;6.7 at {{convert|67.5|C|F}}
* ''[[Listeria monocytogenes]]'' >&nbsp;6.9 at {{convert|65.5|C|F}}
* [[Salmonella]] ser. Typhimurium >&nbsp;6.9 at {{convert|61.5|C|F}}<ref name="Pearce-2012"/>
(A log<sub>10</sub> reduction between 6 and 7 means that 1 bacterium out of 1 million (10<sup>6</sup>) to 10 million (10<sup>7</sup>) bacteria survive the treatment.)

The [[Codex Alimentarius]] ''Code of Hygienic Practice for Milk'' notes that milk pasteurization is designed to achieve at least a 5&nbsp;log<sub>10</sub> reduction of ''Coxiella burnetii''.<ref>{{Cite web|url=http://www.fao.org/fao-who-codexalimentarius/sh-proxy/en/?lnk=1&url=https%253A%252F%252Fworkspace.fao.org%252Fsites%252Fcodex%252FStandards%252FCAC%2BRCP%2B57-2004%252FCXP_057e.pdf|title=Code of Hygienic Practice for Milk and Milk Products|website=Codex Alimentarius|access-date=15 June 2017|archive-date=23 May 2017|archive-url=https://web.archive.org/web/20170523130120/http://www.fao.org/fao-who-codexalimentarius/sh-proxy/en/?lnk=1&url=https%3A%2F%2Fworkspace.fao.org%2Fsites%2Fcodex%2FStandards%2FCAC+RCP+57-2004%2FCXP_057e.pdf|url-status=live}}</ref> The Code also notes that: "The minimum pasteurization conditions are those having bactericidal effects equivalent to heating every particle of the milk to {{convert|72|C|F}} for 15 seconds (continuous flow pasteurization) or {{convert|63|C|F}} for 30 minutes (batch pasteurization)” and that "To ensure that each particle is sufficiently heated, the milk flow in heat exchangers should be turbulent, ''i.e''. the [[Reynolds number]] should be sufficiently high". The point about turbulent flow is important because simplistic laboratory studies of heat inactivation that use test tubes, without flow, will have less bacterial inactivation than larger-scale experiments that seek to replicate conditions of commercial pasteurization.<ref name="Pearce-2001">{{Cite journal|last1=Pearce|first1=Lindsay E.|last2=Truong|first2=H. Tuan|last3=Crawford|first3=Robert A.|last4=Yates|first4=Gary F.|last5=Cavaignac|first5=Sonia|last6=Lisle|first6=Geoffrey W. de|date=2001-09-01|title=Effect of Turbulent-Flow Pasteurization on Survival of Mycobacterium avium subsp.paratuberculosis Added to Raw Milk|journal=Applied and Environmental Microbiology|language=en|volume=67|issue=9|pages=3964–69|doi=10.1128/AEM.67.9.3964-3969.2001|issn=0099-2240|pmc=93116|pmid=11525992|bibcode=2001ApEnM..67.3964P}}</ref>

As a precaution, modern HTST pasteurization processes must be designed with flow-rate restriction as well as divert valves which ensure that the milk is heated evenly and that no part of the milk is subject to a shorter time or a lower temperature. It is common for the temperatures to exceed {{convert|72|C|F}} by {{convert|1.5|-|2|C-change|F-change}}.<ref name="Pearce-2001" />

=== Double pasteurization ===
Pasteurization is not sterilization and does not kill spores. "Double" pasteurization, which involves a secondary heating process, can extend shelf life by killing spores that have germinated.<ref>{{cite web| url = http://nikas.gr/en/faqs/what-double-pasteurization| title = What is double pasteurization?| access-date = 25 January 2021| archive-date = 23 April 2021| archive-url = https://web.archive.org/web/20210423101324/http://nikas.gr/en/faqs/what-double-pasteurization| url-status = dead}}</ref>

The acceptance of double pasteurization varies by jurisdiction. In places where it is allowed, milk is initially pasteurized when it is collected from the farm so it does not spoil before processing. Many countries prohibit the labelling of such milk as "pasteurized" but allow it to be marked "thermized", which refers to a lower-temperature process.<ref>[https://dairyprocessinghandbook.tetrapak.com/chapter/heat-exchangers Heat Exchangers] {{Webarchive|url=https://web.archive.org/web/20210118013909/https://dairyprocessinghandbook.tetrapak.com/chapter/heat-exchangers |date=18 January 2021 }}, Tetrapak Dairy Processing Handbook</ref>