![Pasteurized milk -Japan](https://upload.wikimedia.org/wikipedia/commons/c/c5/Pasteurized_milk_-Japan.jpg)
Pasteurization
or pasteurisation is a process of
food preservation
Food preservation includes processes that make food more resistant to microorganism growth and slow the oxidation of fats. This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit ...
in which packaged and non-packaged foods (such as
milk
Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digestion, digest solid food. Immune factors and immune ...
and fruit
juices
Juice is a drink made from the extraction or pressing of the natural liquid contained in fruit and vegetables. It can also refer to liquids that are flavored with concentrate or other biological food sources, such as meat or seafood, such as ...
) are treated with mild heat, usually to less than , to eliminate
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s and extend
shelf life
Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ...
.
The process is intended to destroy or deactivate
microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s and
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
s that contribute to
food spoilage
Food spoilage is the process where a food product becomes unsuitable to ingest by the consumer. The cause of such a process is due to many outside factors as a side-effect of the type of product it is, as well as how the product is packaged and s ...
or risk of disease, including vegetative
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
, but most
bacterial spores
An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., ...
survive the process.
The process is named after the French microbiologist
Louis Pasteur
Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...
whose research in the 1860s demonstrated that thermal processing would deactivate unwanted microorganisms in
wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
.
Spoilage enzymes are also inactivated during pasteurization. Today, pasteurization is used widely in the
dairy
A dairy is a business enterprise established for the harvesting or processing (or both) of animal milk – mostly from cows or buffaloes, but also from goats, sheep, horses, or camels – for human consumption. A dairy is typically located on ...
industry and other
food processing
Food processing is the transformation of agricultural products into food, or of one form of food into other forms. Food processing includes many forms of processing foods, from grinding grain to make raw flour to home cooking to complex industr ...
industries to achieve
food preservation
Food preservation includes processes that make food more resistant to microorganism growth and slow the oxidation of fats. This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit ...
and
food safety
Food safety (or food hygiene) is used as a scientific method/discipline describing handling, preparation, and storage of food in ways that prevent food-borne illness. The occurrence of two or more cases of a similar illness resulting from t ...
.
By the year 1999, most liquid products were heat treated in a continuous system where heat can be applied using a
plate heat exchanger A plate heat exchanger is a type of heat exchanger that uses metal plates to transfer heat between two fluids. This has a major advantage over a conventional heat exchanger in that the fluids are exposed to a much larger surface area because the fl ...
or the direct or indirect use of hot water and steam. Due to the mild heat, there are minor changes to the nutritional quality and sensory characteristics of the treated foods.
Pascalization
Pascalization, bridgmanization, high pressure processing (HPP) or high hydrostatic pressure (HHP) processing is a method of preserving and sterilizing food, in which a product is processed under very high pressure, leading to the inactivation of ...
or high pressure processing (HPP) and
pulsed electric field (PEF) are non-thermal processes that are also used to pasteurize foods.
History
![Louis Pasteur Experiment](https://upload.wikimedia.org/wikipedia/commons/0/02/Louis_Pasteur_Experiment.svg)
The process of heating wine for preservation purposes has been known in China since AD 1117, and was documented in Japan in the diary ''Tamonin-nikki'', written by a series of monks between 1478 and 1618.
Much later, in 1768, research performed by Italian priest and scientist
Lazzaro Spallanzani
Lazzaro Spallanzani (; 12 January 1729 – 11 February 1799) was an Italian Catholic priest (for which he was nicknamed Abbé Spallanzani), biologist and physiologist who made important contributions to the experimental study of bodily function ...
proved a product could be made "sterile" after thermal processing. Spallanzani boiled meat broth for one hour, sealed the container immediately after boiling, and noticed that the broth did not spoil and was free from microorganisms.
In 1795, a Parisian chef and confectioner named
Nicolas Appert
Nicolas Appert (17 November 1749 – 1 June 1841) was the French inventor of airtight food preservation. Appert, known as the "father of Food Science", was a confectioner. Appert described his invention as a way "of conserving all kinds of food ...
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.
In that same year, the French military offered a cash prize of 12,000
francs
The franc is any of various units of currency. One franc is typically divided into 100 centimes. The name is said to derive from the Latin inscription ''francorum rex'' (King of the Franks) used on early French coins and until the 18th centu ...
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, Appert published ''L'Art de conserver les substances animales et végétales'' ("''The Art of Preserving Animal and Vegetable Substances''"). This was the first cookbook of its kind on modern food preservation methods.
''La Maison Appert'' ( en, The House of Appert), in the town of Massy, near Paris, became the first food-bottling factory in the world,
preserving a variety of foods 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
Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digestion, digest solid food. Immune factors and immune ...
and prepared dishes. 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
A vise or vice (British English) is a mechanical apparatus used to secure an object to allow work to be performed on it. Vises have two parallel jaws, one fixed and the other movable, threaded in and out by a screw and lever.
A vise grip is no ...
. 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 ''appertisation'' in his honor.
Appert's method was so simple and workable that it quickly became widespread. In 1810, British inventor and merchant
Peter Durand
Peter Durand (21 October 1766 – 23 July 1822) was an English merchant who is widely credited with receiving the first patent for the idea of preserving food using tin cans. The patent (No 3372) was granted on August 25, 1810, by King George III ...
, also of French origin, patented his own method, but this time in a
tin can
A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English),
steel packaging, or can is a container for the distribution or storage of goods, made of thin metal. Many cans re ...
, so creating the modern-day process of
canning
Canning is a method of food preservation in which food is processed and sealed in an airtight container (jars like Mason jars, and steel and tin cans). Canning provides a shelf life that typically ranges from one to five years, although u ...
foods. In 1812, Englishmen
Bryan Donkin
Bryan Donkin FRS FRAS
(22 March 1768 – 27 February 1855) developed the first paper making machine and created the world's first commercial canning factory. These were the basis for large industries that continue to flourish today. Bryan Do ...
and John Hall purchased both patents and began producing
preserves
Fruit preserves are preparations of fruits whose main preserving agent is sugar and sometimes acid, often stored in glass jars and used as a condiment or spread.
There are many varieties of fruit preserves globally, distinguished by the method ...
. Just a decade later, Appert's method of canning had made its way to America. Tin can production was 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
A can opener (in North American English and Australian English) or tin opener (used in British English) is a mechanical device used to open tin cans (metal cans). Although canning, preservation of food using tin cans had been practiced since ...
by Robert Yeates in 1855.
A less aggressive method was developed by French chemist
Louis Pasteur
Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...
during an 1864
summer holiday in
Arbois
Arbois () is a Commune in France, commune in the Jura (département), Jura Departments of France, department, in the Bourgogne-Franche-Comté Regions of France, region, eastern France. The river Cuisance passes through the town, which centres on ...
. To remedy the frequent acidity of the local aged
wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
s, he found out experimentally that it is sufficient to heat a young wine to only about for a short time to kill the microbes, and that the wine could subsequently be
aged
Ageing ( BE) or aging ( AE) is the process of becoming older. The term refers mainly to humans, many other animals, and fungi, whereas for example, bacteria, perennial plants and some simple animals are potentially biologically immortal. In ...
without sacrificing the final quality.
In honour of Pasteur, this process is known as "pasteurization".
Pasteurization was originally used as a way of preventing wine and
beer
Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
from souring, and it would be many years before milk was pasteurized. In the United States in the 1870s, before milk was regulated, it was common for milk to contain substances intended to mask spoilage.
Milk
![Milk Vat](https://upload.wikimedia.org/wikipedia/commons/1/1b/Milk_Vat.jpg)
Milk is an excellent
medium
Medium may refer to:
Science and technology
Aviation
*Medium bomber, a class of war plane
*Tecma Medium, a French hang glider design
Communication
* Media (communication), tools used to store and deliver information or data
* Medium of ...
for microbial growth,
and when it is stored at ambient temperature bacteria and other pathogens soon proliferate.
The US
Centers for Disease Control
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
(CDC) says improperly handled raw milk is responsible for nearly three times more hospitalizations than any other food-borne disease source, making it one of the world's most dangerous food products.
Diseases prevented by pasteurization can include
tuberculosis
Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...
,
brucellosis
Brucellosis is a highly contagious zoonosis caused by ingestion of unpasteurized milk or undercooked meat from infected animals, or close contact with their secretions. It is also known as undulant fever, Malta fever, and Mediterranean fever.
The ...
,
diphtheria
Diphtheria is an infection caused by the bacterium '' Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild clinical course, but in some outbreaks more than 10% of those diagnosed with the disease may die. Signs and s ...
,
scarlet fever
Scarlet fever, also known as Scarlatina, is an infectious disease caused by ''Streptococcus pyogenes'' a Group A streptococcus (GAS). The infection is a type of Group A streptococcal infection (Group A strep). It most commonly affects childr ...
, and
Q-fever
Q fever or query fever is a disease caused by infection with '' Coxiella burnetii'', a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, includin ...
; it also kills the harmful bacteria ''
Salmonella
''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is fur ...
'', ''
Listeria
''Listeria'' is a genus of bacteria that acts as an intracellular parasite in mammals. Until 1992, 17 species were known, each containing two subspecies. By 2020, 21 species had been identified. The genus is named in honour of the British pi ...
'', ''
Yersinia
''Yersinia'' is a genus of bacteria in the family Yersiniaceae. ''Yersinia'' species are Gram-negative, coccobacilli bacteria, a few micrometers long and fractions of a micrometer in diameter, and are facultative anaerobes. Some members of ''Ye ...
'', ''
Campylobacter'', ''
Staphylococcus aureus
''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive ...
'', and ''
Escherichia coli O157:H7'', among others.
Prior to industrialization, dairy cows were kept in urban areas to limit the time between milk production and consumption, hence the risk of disease transmission via raw milk was reduced.
As urban densities increased and supply chains lengthened to the distance from country to city, raw milk (often days old) became recognized 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.
Because tuberculosis has a long incubation period in humans, it was difficult to link unpasteurized milk consumption with the disease. In 1892, chemist
Ernst Lederle
Ernst is both a surname and a given name, the German, Dutch, and Scandinavian form of Ernest. Notable people with the name include:
Surname
* Adolf Ernst (1832–1899) German botanist known by the author abbreviation "Ernst"
* Anton Ernst (1975- ...
experimentally inoculated milk from tuberculosis-diseased cows into guinea pigs, which caused them to develop the disease.
In 1910, Lederle, then in the role of Commissioner of Health, introduced mandatory pasteurization of milk in
New York City
New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
.
Developed countries adopted milk pasteurization to prevent such disease and loss of life, and as a result milk is now considered a safer food.
A traditional form of pasteurization by scalding and straining of cream to increase the keeping qualities of
butter
Butter is a dairy product made from the fat and protein components of churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 80% butterfat. It is used at room temperature as a spread, melted as a condiment ...
was practiced in Great Britain in the 18th century and was introduced to
Boston
Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...
in the British Colonies by 1773, although it was not widely practiced in the United States for the next 20 years. Pasteurization of milk was suggested by
Franz von Soxhlet
Franz Ritter von Soxhlet (January 12, 1848 Brno – May 5, 1926 Munich) was a German agricultural chemist from Brno. He invented the Soxhlet extractor in 1879 and in 1886 he proposed pasteurization be applied to milk and other beverages. Soxhl ...
in 1886. In the early 20th century,
Milton Joseph Rosenau established the standards – i.e. low-temperature, slow heating at for 20 minutes – for the pasteurization of milk while at the United States Marine Hospital Service, notably in his publication of ''The Milk Question'' (1912). States in the U.S. soon began enacting mandatory dairy pasteurization laws, with the first in 1947, and in 1973 the U.S. federal government required pasteurization of milk used in any interstate commerce.
The shelf life of refrigerated pasteurized milk is greater than that of
raw milk
Raw milk or unpasteurized milk is milk that has not been pasteurized, a process of heating liquid foods to kill pathogens for safe consumption and extending the shelf life.
Proponents of raw milk have asserted numerous supposed benefits to consu ...
. For example, high-temperature, short-time (
HTST
Flash pasteurization, also called "high-temperature short-time" (HTST) processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, wine, and some dairy products such as milk. Compared with other ...
) pasteurized milk typically has a
refrigerated
The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...
shelf life
Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ...
of two to three weeks, whereas ultra-pasteurized milk can last much longer, sometimes two to three months. When ultra-heat treatment (
UHT
Ultra-high temperature processing (UHT), ultra-heat treatment, or ultra-pasteurization is a food processing technology that sterilizes liquid food by heating it above – the temperature required to kill bacterial endospores – for 2 ...
) is combined with sterile handling and container technology (such as
aseptic packaging), it can even be stored non-refrigerated for up to 9 months.
According to the
Centers for Disease Control
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
, between 1998 and 2011, 79% of dairy-related disease outbreaks in the United States were due to raw milk or cheese products.
They report 148 outbreaks and 2,384 illnesses (with 284 requiring hospitalization), as well as two deaths due to raw milk or cheese products during the same time period.
Medical equipment
Medical equipment, notably respiratory and anesthesia equipment, is often disinfected using hot water, as an alternative to chemical disinfection. The temperature is raised to 70 °C (158 °F) for 30 minutes.
Pasteurization process
![Simple Pasteurization](https://upload.wikimedia.org/wikipedia/commons/c/c8/Simple_Pasteurization.png)
Pasteurization is a mild heat treatment of liquid foods (both packaged and unpackaged) where products are typically heated to below 100 °C. The heat treatment and cooling process are designed to inhibit a phase change of the product. The
acidity
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
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 (
pH <4.6), such as fruit juice and
beer
Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
, the heat treatments are designed to inactivate enzymes (pectin
methylesterase and
polygalacturonase
Endo-polygalacturonase (EC 3.2.1.15, pectin depolymerase, pectolase, pectin hydrolase, and poly-α-1,4-galacturonide glycanohydrolase; systematic name (1→4)-α-D-galacturonan glycanohydrolase (endo-cleaving)) is an enzyme that hydrolyzes the α- ...
in fruit juices) and destroy spoilage microbes (yeast and
lactobacillus
''Lactobacillus'' is a genus of Gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria. Until 2020, the genus ''Lactobacillus'' comprised over 260 phylogenetically, ecologically, and metabolically diver ...
). Due to the low pH of acidic foods, pathogens are unable to grow. The shelf-life is thereby extended several weeks. In less acidic foods (pH >4.6), such as milk and liquid eggs, the heat treatments are designed to destroy pathogens and spoilage organisms (yeast and molds). Not all spoilage organisms are destroyed under pasteurization parameters, thus subsequent refrigeration is necessary.
High-temperature short-time (HTST) pasteurization, such as that used for milk ( for 15 seconds) ensures safety of milk and provides a refrigerated shelf life of approximately two weeks. In ultra-high-temperature (UHT) pasteurization, milk is pasteurized at for 1–2 seconds, which provides the same level of safety, but along with the packaging, extends shelf life to three months under refrigeration.
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
Thermal shock is a type of rapidly transient mechanical load.
By definition, it is a mechanical load caused by a rapid change of temperature of a certain point.
It can be also extended to the case of a thermal gradient, which makes different par ...
. When plastic or metal packaging is used, the risk of thermal shock is low, so steam or hot water is used.
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 A plate heat exchanger is a type of heat exchanger that uses metal plates to transfer heat between two fluids. This has a major advantage over a conventional heat exchanger in that the fluids are exposed to a much larger surface area because the fl ...
s are used for low-
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
products such as animal milks, nut milks 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. Scraped-surface heat exchangers 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.
Shell and tube heat exchangers are designed for the pasteurization of foods that are
non-Newtonian fluid
A non-Newtonian fluid is a fluid that does not follow Newton's law of viscosity, i.e., constant viscosity independent of stress. In non-Newtonian fluids, viscosity can change when under force to either more liquid or more solid. Ketchup, for exa ...
s, such as dairy products, tomato
ketchup
Ketchup or catsup is a table condiment with a sweet and tangy flavor. The unmodified term ("ketchup") now typically refers to tomato ketchup, although early recipes used egg whites, mushrooms, oysters, grapes, mussels, or walnuts, among other ...
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.
The benefits of using a
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
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 energy-efficiency
* Greater throughput
After being heated in a heat exchanger, the product flows through a hold tube for a set period of time to achieve the required treatment. If pasteurization temperature or time is not achieved, a flow diversion valve is used to divert under-processed product back to the raw product tank. 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
The enzyme alkaline phosphatase (EC 3.1.3.1, alkaline phosphomonoesterase; phosphomonoesterase; glycerophosphatase; alkaline phosphohydrolase; alkaline phenyl phosphatase; orthophosphoric-monoester phosphohydrolase (alkaline optimum), systematic ...
, 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. For
liquid eggs, the effectiveness of the heat treatment is measured by the residual activity of
α-amylase
α-Amylase is an enzyme (EC 3.2.1.1; systematic name 4-α-D-glucan glucanohydrolase) that hydrolyses α bonds of large, α-linked polysaccharides, such as starch and glycogen, yielding shorter chains thereof, dextrins, and maltose:
:Endohyd ...
.
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, and so a number of different pasteurization standards were in use. By 1943, both HTST pasteurization conditions of for 15 seconds, as well as batch pasteurization conditions of 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. Complete inactivation of ''
Coxiella burnetii
''Coxiella burnetii'' is an obligate intracellular bacterial pathogen, and is the causative agent of Q fever. The genus ''Coxiella'' is morphologically similar to ''Rickettsia'', but with a variety of genetic and physiological differences. ''C. ...
'' (which was thought at the time to cause
Q fever
Q fever or query fever is a disease caused by infection with ''Coxiella burnetii'', a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including ...
by oral ingestion of infected milk) as well as of ''
Mycobacterium tuberculosis
''Mycobacterium tuberculosis'' (M. tb) is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' has an unusual, waxy coating on its c ...
'' (which causes
tuberculosis
Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...
) were later demonstrated. For all practical purposes, these conditions were adequate for destroying almost all
yeast
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...
s,
mold
A mold () or mould () is one of the structures certain fungus, fungi can form. The dust-like, colored appearance of molds is due to the formation of Spore#Fungi, spores containing Secondary metabolite#Fungal secondary metabolites, fungal seco ...
s, and common
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.
The mean log
10 reductions and temperatures of inactivation of the major milk-borne pathogens during a 15-second treatment are:
* ''
Staphylococcus aureus
''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive ...
'' > 6.7 at
* ''
Yersinia enterocolitica
''Yersinia enterocolitica'' is a Gram-negative, bacillus-shaped bacterium, belonging to the family Yersiniaceae. It is motile at temperatures of 22–29° C (72–84 °F), but becomes nonmotile at normal human body temperature. ''Y. enterocoliti ...
'' > 6.8 at
* Pathogenic ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' > 6.8 at
* ''
Cronobacter sakazakii
''Cronobacter sakazakii'', which before 2007 was named ''Enterobacter sakazakii'', is an opportunistic Gram-negative, rod-shaped, pathogenic bacterium that can live in very dry places, otherwise known as xerotolerance. ''C. sakazakii'' utilizes a ...
'' > 6.7 at
* ''
Listeria monocytogenes
''Listeria monocytogenes'' is the species of pathogenic bacteria that causes the infection listeriosis. It is a facultative anaerobic bacterium, capable of surviving in the presence or absence of oxygen. It can grow and reproduce inside the host' ...
'' > 6.9 at
*
Salmonella
''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is fur ...
ser. Typhimurium > 6.9 at
(A log
10 reduction between 6 and 7 means that 1 bacterium out of 1 million (10
6) to 10 million (10
7) bacteria survive the treatment.)
The
Codex Alimentarius
The Codex Alimentarius () is a collection of internationally recognized standards, codes of practice, guidelines, and other recommendations published by the Food and Agriculture Organization of the United Nations relating to food, food production ...
''Code of Hygienic Practice for Milk'' notes that milk pasteurization is designed to achieve at least a 5 log
10 reduction of ''Coxiella burnetii''. The Code also notes that: "The minimum pasteurization conditions are those having bactericidal effects equivalent to heating every particle of the milk to 72 °C for 15 seconds (continuous flow pasteurization) or 63 °C 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
In fluid mechanics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be domi ...
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.
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 72 °C by 1.5 °C or 2 °C.
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.
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.
Effects on nutritional and sensory characteristics of foods
Because of its mild heat treatment, pasteurization increases the shelf-life by a few days or weeks.
However, this mild heat also means there are only minor changes to heat-labile vitamins in the foods.
Milk
According to a systematic review and meta-analysis,
it was found that pasteurization appeared to reduce concentrations of vitamins
B12
Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. It ...
and
E, but it also increased concentrations of
vitamin A
Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably bet ...
. Apart from meta-analysis, it is not possible to draw conclusions about the effect of pasteurization on vitamins A, B12, and E based merely on consultation of the vast literature available.
Milk is not an important source of vitamins B12 or E in the North American diet, so the effects of pasteurization on the adult daily intake of these vitamins is negligible.
[U.S. Department of Agriculture. 2001. Dietary reference intakes-recommended intakes for individuals. National Academy of Sciences. Institute of Medicine, Food and Nutrition Board. Available at]
[U.S. Department of Agriculture. 2009. "What's in the foods you eat" search tool. Available at: "https://www.ars.usda.gov/northeast-area/beltsville-md/beltsville-human-nutrition-research-center/food-surveys-research-group/docs/whats-in-the-foods-you-eat-emsearch-toolem/ ] However, milk is considered an important source of vitamin A,
and because pasteurization appears to increase vitamin A concentrations in milk, the effect of milk heat treatment on this vitamin is a not a major public health concern.
Results of meta-analyses reveal that pasteurization of milk leads to a significant decrease in
vitamin C
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...
and
folate
Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and ...
, but milk is also not an important source of these vitamins.
A significant decrease in
vitamin B2
Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved in e ...
concentrations was found after pasteurization. Vitamin B2 is typically found in bovine milk at concentrations of 1.83 mg/liter. Because the recommended daily intake for adults is 1.1 mg/day,
milk consumption greatly contributes to the recommended daily intake of this vitamin. With the exception of B2, pasteurization does not appear to be a concern in diminishing the
nutritive value of milk because milk is often not a primary source of these studied vitamins in the North American diet.
Sensory effects
Pasteurization also has a small but measurable effect on the sensory attributes of the foods that are processed.
In fruit juices, pasteurization may result in loss of volatile aroma compounds.
Fruit juice products undergo a
deaeration
Deaeration is the removal of air molecules (usually meaning oxygen) from another gas or liquid. It can refer to:
*Use of a deaerator.
*Degasification
Degassing, also known as degasification, is the removal of dissolved gases from liquids, espec ...
process prior to pasteurization that may be responsible for this loss. Deaeration also minimizes the loss of nutrients like vitamin C and
carotene
The term carotene (also carotin, from the Latin ''carota'', "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the exc ...
.
To prevent the decrease in quality resulting from the loss in volatile compounds, volatile recovery, though costly, can be utilized to produce higher-quality juice products.
In regards to color, the pasteurization process does not have much effect on pigments such as
chlorophyll
Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...
s,
anthocyanin
Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
s and
carotenoid
Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, and Fungus, fungi. Carotenoids give the characteristic color to pumpki ...
s in plants and animal tissues. In fruit juices,
polyphenol oxidase
Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme involved in fruit browning, is a tetramer that contains four atoms of copper per molecule.
PPO may accept monophenols and/or ''o''-diphenols as substrates. The ...
(PPO) is the main enzyme responsible for causing browning and color changes. However, this enzyme is deactivated in the deaeration step prior to pasteurization with the removal of oxygen.
In milk, the color difference between pasteurized and raw milk is related to the
homogenization
Homogeneity is a sameness of constituent structure.
Homogeneity, homogeneous, or homogenization may also refer to:
In mathematics
*Transcendental law of homogeneity of Leibniz
* Homogeneous space for a Lie group G, or more general transformati ...
step that takes place prior to pasteurization. Before pasteurization milk is homogenized to emulsify its fat and water-soluble components, which results in the pasteurized milk having a whiter appearance compared to raw milk.
For vegetable products, color degradation is dependent on the temperature conditions and the duration of heating.
Pasteurization may result in some textural loss as a result of enzymatic and non-enzymatic transformations in the structure of
pectin
Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component of ...
if the processing temperatures are too high as a result. However, with mild heat treatment pasteurization, tissue softening in the vegetables that causes textural loss is not of concern as long as the temperature does not get above .
Novel pasteurization methods
Other thermal and non-thermal processes have been developed to pasteurize foods as a way of reducing the effects on nutritional and sensory characteristics of foods and preventing degradation of heat-labile nutrients. Pascalization or high pressure processing (HPP),
pulsed electric field (PEF),
ionising radiation
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
,
high pressure homogenisation
High may refer to:
Science and technology
* Height
* High (atmospheric), a high-pressure area
* High (computability), a quality of a Turing degree, in computability theory
* High (tectonics), in geology an area where relative tectonic uplift ...
,
UV decontamination
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
,
pulsed high intensity light,
high intensity laser,
pulsed white light,
high power ultrasound
High may refer to:
Science and technology
* Height
* High (atmospheric), a high-pressure area
* High (computability), a quality of a Turing degree, in computability theory
* High (tectonics), in geology an area where relative tectonic uplift to ...
,
oscillating magnetic fields
Oscillation is the repetitive or Periodic function, periodic variation, typically in time, of some measure about a central value (often a point of Mechanical equilibrium, equilibrium) or between two or more different states. Familiar examples o ...
,
high voltage arc discharge
High may refer to:
Science and technology
* Height
* High (atmospheric), a high-pressure area
* High (computability), a quality of a Turing degree, in computability theory
* High (tectonics), in geology an area where relative tectonic uplift to ...
, and
streamer plasma
Streamer or streamers may refer to:
* a person who streams online on an internet platform like twitch or youtube
* Pennon, a small pointed flag
* Streamer, a kind of confetti consisting of strips of paper or other material
* Streamer, a common na ...
are examples of these non-thermal pasteurization methods that are currently commercially utilized.
Microwave volumetric heating (MVH) is the newest available pasteurization technology. It uses
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...
s to heat liquids, suspensions, or semi-solids in a continuous flow. Because MVH delivers energy evenly and deeply into the whole body of a flowing product, it allows for gentler and shorter heating, so that almost all heat-sensitive substances in the milk are preserved.
Low Temperature, Short Time
Low or LOW or lows, may refer to:
People
* Low (surname), listing people surnamed Low
Places
* Low, Quebec, Canada
* Low, Utah, United States
* Lo Wu station (MTR code LOW), Hong Kong; a rail station
* Salzburg Airport (ICAO airport code: LOW ...
(LTST) is a patented method that implies spraying droplets in a chamber heated below the usual pasteurization temperatures. It takes several thousandth of a second to treat liquid products, so the method is also known as the millisecond technology (MST). It significantly extends the shelf life of products (50+ days) when combined with HTST without damaging the nutrients or flavor. LTST has been commercial since 2019.
Products that are commonly pasteurized
*
Beer
Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
*
Canned food
Canning is a method of food preservation in which food is processed and sealed in an airtight container (jars like Mason jars, and steel and tin cans). Canning provides a shelf life that typically ranges from one to five years, although un ...
*
Dairy products
Dairy products or milk products, also known as lacticinia, are Food product, food products made from (or containing) milk. The most common dairy animals are cow, water buffalo, dairy goat, nanny goat, and Sheep, ewe. Dairy products include commo ...
*
Eggs
Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
*
Milk
Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digestion, digest solid food. Immune factors and immune ...
*
Juice
Juice is a drink made from the extraction or Cold-pressed juice, pressing of the natural liquid contained in fruit and vegetables. It can also refer to liquids that are flavored with concentrate or other biological food sources, such as meat ...
s
*
Low alcoholic beverages
*
Syrup
In cooking, a syrup (less commonly sirup; from ar, شراب; , beverage, wine and la, sirupus) is a condiment that is a thick, viscous liquid consisting primarily of a solution of sugar in water, containing a large amount of dissolved sugars ...
s
*
Vinegar
Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to et ...
*
Water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
*
Wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
s
See also
*
Food irradiation
Food irradiation is the process of exposing food and food packaging to ionizing radiation, such as from gamma rays, x-rays, or electron beams. Food irradiation improves food safety and extends product shelf life (preservation) by effectively ...
*
Flash pasteurization
Flash pasteurization, also called "high-temperature short-time" (HTST) processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, wine, and some dairy products such as milk. Compared with other ...
*
Pascalization
Pascalization, bridgmanization, high pressure processing (HPP) or high hydrostatic pressure (HHP) processing is a method of preserving and sterilizing food, in which a product is processed under very high pressure, leading to the inactivation of ...
*
Homogenization
Homogeneity is a sameness of constituent structure.
Homogeneity, homogeneous, or homogenization may also refer to:
In mathematics
*Transcendental law of homogeneity of Leibniz
* Homogeneous space for a Lie group G, or more general transformati ...
*
Pasteurized eggs
Pasteurized eggs are eggs that have been pasteurized in order to reduce the risk of food-borne illness in dishes that are not cooked or are only lightly cooked. They may be sold as liquid egg products or pasteurized in the shell.
Rationale
Th ...
*
Solar water disinfection
Solar water disinfection, in short SODIS, is a type of portable water purification that uses solar energy to make biologically-contaminated (e.g. bacteria, viruses, protozoa and worms) water safe to drink. Water contaminated with non-biological ag ...
*
Thermoduric bacteria Thermoduric bacteria are bacteria which can survive, to varying extents, the pasteurisation process. Species of bacteria which are thermoduric include Bacillus, Clostridium
''Clostridium'' is a genus of anaerobic, Gram-positive bacteria. Speci ...
*
Food preservation
Food preservation includes processes that make food more resistant to microorganism growth and slow the oxidation of fats. This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit ...
*
Food storage
Food storage is a way of decreasing the variability of the food supply in the face of natural, inevitable variability. p.507 It allows food to be eaten for some time (typically weeks to months) after harvest rather than solely immediately. I ...
*
Food microbiology
*
Sterilization
*
Thermization
Thermization, also spelled thermisation, is a method of sanitizing raw milk with low heat. "Thermization is a generic description of a range of subpasteurization heat treatments (57 to 68°C × 10 to 20 s) that markedly reduce the number of spoilag ...
References
Further reading
Raw milk expert testimony dated: April 25, 2008 Case: Organic Dairy Company, LLC, and Claravale Farm, Inc., Plaintiffs, vs. No. CU-07-00204 State of California and A.G. Kawamura, Secretary of California Department of Food and Agriculture, – Expert Witnesses: Dr. Theodore Beals & Dr. Ronald Hull* An alternate view on the alleged safety of pasteurized vs. natural milk from Johns Hopkins University:
Unraveling the mysteries of extended shelf life*
{{Authority control
Food science
Unit operations
Food preservation
Louis Pasteur
Industrial processes