Editing Pasteurization (section)

====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" />