The Pasteurization (also pasteurisation) is the process of subjecting one food , usually liquid , to a temperature approximately 80 degrees for a few seconds and then cooling rapidly, in order to destroy germs and prolong its conservation .


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  • 1 Definition
  • 2 Objectives
  • 3 Pasteurization processes
    • 1 HTST process
    • 2 UHT process
  • 4 Standard Regulatory Bodies
  • 5 Dynamics of pasteurization
  • 6 Milk pasteurization
    • 1 Alternative methods to pasteurization of milk
    • 2 Diseases it prevents
    • 3 Are current pasteurization methods adequate?
  • 7 Pasteurization of juices
    • 1 Common microorganisms in juices
    • 2 Effects of pasteurization on juices
  • 8 Recent research
  • 9 Sources


Pasteurization is the process of heating liquids (generally food) in order to reduce pathogens, such as bacteria , protozoa , molds and yeasts , etc. that may exist. The process is named in honor of its discoverer, the French scientist Louis Pasteur (1822-1895). The first pasteurization was completed on April 20, 1882, and was carried out by Pasteur and Claude Bernard.


One of the objectives of the treatment is the partial sterilization of food liquids, altering as little as possible the physical structure and the chemical components of it. After the pasteurization operation, the treated products are hermetically sealed for security purposes. Unlike sterilization, pasteurization does not destroy spores of microorganisms, nor does it kill all cells of thermophilic microorganisms. Pasteur’s scientific breakthrough improved quality of life by allowing products such as milkcould be transported without decomposing. In pasteurization, the primary objective is not the “elimination of pathogens” but the reduction of their populations, to levels that do not cause food poisoning (assuming that the pasteurized product has been properly refrigerated and that it is consumed before the expiration date ). Pasteurization is being the subject of doubts in certain groups of consumers throughout the world due to the existing doubts about the destruction of vitamins and alteration of the organoleptic properties of ( taste and quality ) of the food products treated.

Pasteurization processes

Pasteurization generally uses temperatures below the boiling point since, in most cases, temperatures above this value irreversibly affect the physical and chemical characteristics of the food product, this is the case, for example, in milk if the point is passed. By boiling, the casein micelles are irreversibly added (or in other words “curdled”). Today there are two types of processes: pasteurization at high temperatures / short time (HTST of English: High Temperature / Short Time) and the process at ultra-high temperatures (UHT – also Ultra-High Temperature).

HTST process

This method is used in bulk liquids: milk, fruit juices, beer , etc. As a general rule, it is the most convenient since it exposes the food to high temperatures for a short period of time and also the industry needs little equipment to be able to carry it out, thus reducing equipment maintenance costs. Among the disadvantages is the need for highly qualified personnel capable of intensive controls on production. There are two different methods under the category of HTST pasteurization: “batch” and “continuous flow.”

  • In the “batch” process (also known as Vat Pasteurization or Vat Pasteurization) a large quantity of milk is heated in an airtight container ( Autoclave ) to a temperature that reaches 63 ° C to 68 ° C during an interval of 30 minutes, followed immediately cooling to 4 ° C to avoid the proliferation of organisms.
  • In the continuous flow process, the milk is held between two metal plates or also called a plate heat exchanger (PHE) or a tube-shaped heat exchanger.

UHT process

The UHT process is continuous flow and keeps the milk at a higher temperature than that used in the HTST process and can be around 138 ° C for a period of at least two seconds. Due to this exposure period, although short, there is minimal degradation of the food. Milk when labeled “pasteurized” has generally been treated with the HTST process, while milk labeled “ultra-pasteurized” or simply “UHT” must be understood to have been treated by the UHT method. The technological challenge in the 21st century is to be able to reduce as much as possible the period of exposure to high food temperatures, making the transition as fast as possible and reducing the impact on the degradation of the organoleptic properties of food,You microwave . This method is very suitable for slightly acidic liquid foods , such as fruit juices and vegetable juices .

Standard Regulatory Bodies

Pasteurization methods correspond to a series of standardized methods controlled by the agencies in charge of monitoring the quality of food in each country (some examples are the USDA in the United States and the Food Standards Agency in the United Kingdom). These agencies require and monitor that HTST-pasteurized dairy carries the proper food label. As a general rule, there are different standards depending on the dairy products to be processed, the main factor to take into account is the fat content of the product, in this way the pasteurization standards of the cream differ from the standards used for skimmed milk and the standards to pasteurize the cheeseThey are designed and implemented in such a way that the enzymes that process phosphates , useful for maintaining the cutting and texture properties of cheeses, are not destroyed . Standard HTST pasteurization methods have been designed to achieve a shelf life extension of about 5 days (ie 0.00001 times the original period) by reducing the number of microorganisms in milk. This method is considered adequate for the reduction of populations of almost all pathogenic bacteria, spores, and any other microorganism resistant to high temperatures (including particularly Mycobacterium tuberculosis, which causes tuberculosis, and Coxiella burnetii, which causes fever.Q). The HTST pasteurization process is designed so that the products are heated evenly, avoiding that only some parts are subjected to sterilization while others do not.

Dynamics of pasteurization

Pasteurization is a process that follows first-order chemical kinetics , if we call N as the number of living microorganisms at a given temperature T of exposure, and Not the population of microorganisms initially. And Kd is the kinetic constant of death due to temperature (death rate of microorganisms), the population decrease then depends on the following formula:

N = No e – Kd T

This formula is essential to determine the evolution of a population as a function of temperature. A great dependence on the exposure temperature T can be seen in it. The formula is the foundation, moreover, of the so-called survival diagrams in the food industry representing log (N / No) versus the exposure time at a fixed temperature T. Typically, heat survival graphs appear as straight lines on a semi-logarithmic scale. The correlation between speedof microorganism death and temperature follows the Arrhenius equation. An important factor assigned to each microorganism is the so-called decimal reduction time or also the D-value of a microorganism and it is defined as the time necessary for its population to be reduced by 90% in the treated product at a given temperature. It is an expression of the resistance of a microorganism to the effect of temperature . Its expression is:

DT = \ frac {\ Delta t} {\ log No – \ log N}

Where t is the period of time to which the sample is exposed and No is the initial population and N is the final one. Different D-values ​​can be obtained for a given microorganism, or for a particular food process, by determining survivors at different temperatures. High values ​​of D indicate that the microorganism is more resistant than others that have a lower value. There are other values ​​such as the “thermal resistance constant”, often referred to as the “z value” and is defined as the difference in temperatures necessary to cause a 90% reduction in the D value.

Milk pasteurization

Since its origins pasteurization has been associated with milk, the first researcher who suggested this process for this dairy product was the German agricultural chemist Franz von Soxhlet in 1886 . Milk is generally an alkaline medium with a pH> 4.5. Milk cowPasteurized by the HTST method and that has been properly refrigerated has an extended shelf life that can reach two or three weeks, while ultra-pasteurized milk can have an extended shelf life that ranges between two or three months. Longer storage times (even without refrigeration) can be achieved when UHT pasteurization is combined with handling using sterile container technologies. At the same time that the colonies are reduced, the most heat-sensitive microorganisms, such as coliforms, are also eliminated in the milk, inactivating the alkaline phosphatase. Despite applying pasteurization, the treated milk still contains microbial activity, generally lactic acid bacteria (non-pathogenic although fermentative), and refrigeration is necessary.

Alternative methods to pasteurization of milk

In addition to the standard HTST and UHT pasteurization methods, there are other similar methods and techniques that are less well known to consumers. The first technique is called “batch pasteurization” and is developed by heating large batches (batches) of milk to a temperature below 68 ° C. The other technique is called Higher-Heat / Shorter Time (HHST) and is similar to the process described for HTST and UHT in terms of time interval and temperature. Pasteurization causes denaturation of proteins causing some organoleptic properties of milk to be affected.

Diseases it prevents

Consuming raw, unpasteurized animal milk exposes you to certain risks of contact with disease-causing organisms and bacteria. In some countries their sale has been banned. Some of the diseases avoided with pasteurization of milk are tuberculosis (Koch’s bacillus), diphtheria , polio, salmonellosis , scarlet fever, and typhoid fevers. Many of these diseases , today, do not have a great relevance due to the widespread use of pasteurization processes in the early stages of milk handling.

Are current pasteurization methods adequate?

The pasteurization of milk has gradually been the subject of growing controversy, on the one hand it has been discovered that some pathogenic organisms have developed a resistance to population decline with temperature, managing to survive pasteurization in significant quantities. Researchers have developed more sensitive diagnostics such as the polymerase chain reaction (also known as PCR for short) that have made it possible to see the survival of strains of different microorganisms to pasteurization of milk. Pasteurization under certain conditions has been found to destroy vitamin A and vitamin B

Juice pasteurization

Packaged juices (and even nectars) are subjected to two different types of pasteurization processes: on the one hand there are unprocessed juices (raw) and on the other the ultra-pasteurized juices or sterile juices. Juice producers are familiar with pasteurization processes and both the Vat or “batch” process (used in small-size producers) and UHT (used in larger producers). The HTST method is accepted in the industry as it does not produce an appreciable flavor degeneration. Pasteurization is very effective in juices because it is an acidic medium and prevents the proliferation of sporulated microorganisms: the most resistant to high temperatures. In many countries like the United States, 95% of the juices sold are pasteurized,food hygiene that indicates to the consumer that he is taking a “raw juice”.

Common microorganisms in juices

Depending on the origin of the juices, there are different microorganisms included that must be reduced in the total concentration of their populations by pasteurizing them, in this way, the apple juice has: Salmonella typhimurium, cryptosporidium and E. coli. In orange juice it is usual: Bacillus cereus, Salmonella typhi, Salmonella hartford. In some vegetable juices such as carrot juice : Clostridium botulinum.

Effects of pasteurization in juices

The juices can suffer alterations in the color of the drink, tending to brown due to the enzymatic deterioration of the polyphenoloxidase. This is due in part to the presence of oxygen in the liquid, this is the reason why juices and nectars are usually released from the air before entering the pasteurization process. In the same way, the loss of vitamin C and carotene is diminished by previous aeration.

Recent research

It has been found that in particular the organism Mycobacterium avium subspecies paratuberculosis (MAP), which causes Johne’s disease in slaughter animals and it is suspected that also in Crohn’s disease in humans, has been discovered as a survivor after pasteurization of certain dairy foods in the US, UK, Greece and the Czech Republic. The authorities in charge of monitoring the quality of food in the United Kingdom decided to re-evaluate the pasteurization standards in view of the survival of certain species such as MAP. A current method is flash pasteurization, which involves shorter exposure times to high temperatures and seems to be an adequate method for preserving the organoleptic properties of foods, better preserving their flavor and texture. Cold pasteurization is sometimes used as a synonym for ionizing radiation (see food irradiation) or other meanings (such as chemicals) to reduce bacteria populations in food. Food irradiation is sometimes also referred to as “electronic pasteurization”. The possibility of extending pasteurization to non-fluid foods such asbeef beef.


A breakthrough in non-intrusively pasteurization that solves many problems of the canning industry is denominated electromagnetic Pasteurization of liquid foods, which uses microwaves at 2.45 GHz frequency to activate the thermal processes, this method has proven its efficiency the pasteurization of the water. There are studies oriented to the Third World in which it is possible to carry out what is called solar pasteurization, the idea is based on the idea of ​​solar cooking and that it is not necessary to bring liquids to a boil to achieve pasteurization. This measure tries to prevent the cause of diseases caused by the ingestion of contaminated water, being able to pasturize with this method with temperatures over 56º C. The method is known as “Water pasturization” in which certain elements capable of indicate the state of pasteurization of the water and its safe ingestion capacity, one of the most used is the “Water pasteurization indicator” (WAPI).


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