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A photo of test tubes. The one on the left has white tape, the one on the right has the same white tape but it now has a black line.
The white strips on autoclave tape (left tube) turn dark during a successful autoclave run (right tube). (credit: modification of work by Brian Forster)

Pasteurization

Although complete sterilization is ideal for many medical applications, it is not always practical for other applications and may also alter the quality of the product. Boiling and autoclaving are not ideal ways to control microbial growth in many foods because these methods may ruin the consistency and other organoleptic (sensory) qualities of the food. Pasteurization is a form of microbial control for food that uses heat but does not render the food sterile. Traditional pasteurization kills pathogens and reduces the number of spoilage-causing microbes while maintaining food quality. The process of pasteurization was first developed by Louis Pasteur in the 1860s as a method for preventing the spoilage of beer and wine. Today, pasteurization is most commonly used to kill heat-sensitive pathogens in milk and other food products (e.g., apple juice and honey) ( [link] ). However, because pasteurized food products are not sterile, they will eventually spoil.

The methods used for milk pasteurization balance the temperature and the length of time of treatment. One method, high-temperature short-time (HTST) pasteurization , exposes milk to a temperature of 72 °C for 15 seconds, which lowers bacterial numbers while preserving the quality of the milk. An alternative is ultra-high-temperature (UHT) pasteurization , in which the milk is exposed to a temperature of 138 °C for 2 or more seconds. UHT pasteurized milk can be stored for a long time in sealed containers without being refrigerated; however, the very high temperatures alter the proteins in the milk, causing slight changes in the taste and smell. Still, this method of pasteurization is advantageous in regions where access to refrigeration is limited.

Pasteurization shows an image of a large machine. To the left is HTST pasteurization where milk is heated at 72 degrees C for 15 seconds, then boiled and refrigerated. To the right is UHT pasteurization where milk is heated at 138 degrees C for 2 or more seconds, then sealed in airtight containers for up to 90 days without refrigeration. To the bottom is the following test: milkborne organisms killed by pasteurization: Campylobacter jejuni, Coxiella burnetii, Listeria monocytogenes, Escherichia coli O157:H7, Mycobacterium tuberculosis, M. paratuberculosis, Salmonella spp., Yersinia enterocolitica.
Two different methods of pasteurization, HTST and UHT, are commonly used to kill pathogens associated with milk spoilage. (credit left: modification of work by Mark Hillary; credit right: modification of work by Kerry Ceszyk)
  • In an autoclave, how are temperatures above boiling achieved?
  • How would the onset of spoilage compare between HTST-pasteurized and UHT-pasteurized milk?
  • Why is boiling not used as a sterilization method in a clinical setting?

Refrigeration and freezing

Just as high temperatures are effective for controlling microbial growth, exposing microbes to low temperatures can also be an easy and effective method of microbial control, with the exception of psychrophiles , which prefer cold temperatures (see Temperature and Microbial Growth ). Refrigerators used in home kitchens or in the laboratory maintain temperatures between 0 °C and 7 °C. This temperature range inhibits microbial metabolism, slowing the growth of microorganisms significantly and helping preserve refrigerated products such as foods or medical supplies. Certain types of laboratory cultures can be preserved by refrigeration for later use.

Questions & Answers

what is cell?
Anita Reply
the cell is the functional and structural unit of the body
Ruth
yes ur right
Kasigwa
who add me
Wali
hy
Katta
hy
Shivangi
basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life.
Haru
hi
Ruth
hi
Haru
coming Oct 2 I have a exam on microbiology
Haru
okay all the best
Ruth
hi
sachin
hi
Ruth
this is not the correct answer
Alanna Reply
why
Hayat
why not
Zaajid
what is the correct answer?
vannessa
where is question
Zaajid
ask you question
Zaajid
What are mitochondria
Hayat
what is mitochondria
Hayat
who is the father of microbiology
T-
not
Hayat
Antonie Van Luweenhoek
Ravikumar
Mitochondria is the powerhouse of the Cell. And is the cell organelle which helps cell in generation of energy by Cellular Respiration
Ravikumar
what is a vacual
Star Reply
What is microbiology
Nji Reply
it is the study of microscopic organisms and basically their relation to the environment
Tenucharity
what is elements
Erneet Reply
an Element is a substance that can not be further decomposed by ordinary chemical means.
vannessa
can i get notes of biochemistry
Sneha Reply
yep why not
Abdullah
what is microbiology?
Gayanjali Reply
what is malaria
Gayanjali
bios- life/living things micro- small things that cannot be seen with the naked eye In other words the study of living things that cannot be seen with the naked eye but with the help of a microscope
Coltuneac
logos- science
Coltuneac
it is 10 to the power minus 6 biology which studies life forms on those scales including metabolism , physiology, nutrition requirements
barun
what are prokarytes
NDIMUKIKA Reply
A prokaryotic is a unicellular organanism that lacks a membrane bound nucleus ,mitochondria or other any membrane bound organelle. .......
Maryam
in prokaryotic nucleus is not developed and cell organelles are absent
Harshad
how is one who is feeling blockage in the chest with mucus be diagnosed
Essy Reply
be talking sepitol every morning
Ikenna
is that all?
Ven.phumie
What is prions
Sangeeta Reply
is tuberculosis a viral infection?
hildar Reply
No. It is a Bacterial Infection.
Orooj
what are zn staining
Evelyn Reply
full meaning zeil neelson staining
kezia
By using zn stain we diagnose / examine acid fast bacilli .
Deepak
explain hw bacteria grows
Kanyago Reply
Hw does bacteria grow?
Kanyago
Binary fission
Sangeeta
three successive phase comes in bacteria growth i.e lag phase/adaptation phase ,log phase/exponential phase ,death phase when it is in fermentation process .
Deepak
introduction to virology
Dongyile Reply
is the study of virus
FADAYOMI
Virology
Sangeeta
study of virus which can be seen by using electron microscope i.e below 1micron in size . It requires a host cell to multiply own number to proliferate itself .
Deepak
what are some five benefits of studying microbiology
Joyce Reply
please I'm waiting for answers
Joyce
microbio is very important! 1.) microbes thought to have evolved into our cells 2.) they keep us healthy 3.) they can cause disease and illness 4.) good for bioremediation 5.) show evolution in real time(observable) 6.) make the earth a liveable place (make more o2 than plants)
just
What fields are interesting to study when you are doing your postgraduate degree
Noxolo

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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