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Pasteurization
 
Dr Usama Fouad Shaalan MD- PhD MiniEncyclopedia الموسوعه المصغره للدكتور  أسامه فؤاد شعلان
 

Pros and Cons of Pasteurization

 

Pasteurization kills organisms–such as salmonella, listeria, and brucella–that can make you sick or cause food to spoil but opponents argue that it changes foods’ flavor and damages beneficial vitamins and minerals. Meanwhile, the FDA claims the effects on nutrients are negligible. Here are the pros and cons of common types of pasteurization.

Ultra-high temperature (UHT)
Used on: Milk, fruit juices, dairy creamers, cheese sauces, yogurt, wine with less than 14 percent alcohol content
How it’s done: Product is heated to at least 280 degrees for 1-2 seconds. Most common in countries where many residents don’t own refrigerators.
Pros: Cost-effective; minimal changes in color, flavor, and texture; extends shelf life by months.
Cons: Milk can taste “cooked.”

High Temperature Short Time (HTST) or Flash
Used on: Milk, most juices, beer, almonds
How it’s done: Food is heated to 160 degrees for 15 seconds and then rapidly cooled to 40 degrees. Most frequently used for milk in the U.S.
Pros: Pasteurized juices can have shelf lives of up to a year.
Cons: Products require refrigeration; opponents say pasteurizing almonds kills the nut’s ability to sprout.

Vat
Used on: Most American-made hard and soft cheeses, yogurt, and buttermilk
How it’s done: Louis Pasteur’s original method heats product to 145 degrees in a large vat for 30 minutes.
Pros: Milk retains flavor.
Cons: Semi-obsolete because of time intensiveness and higher cost.

Unpasteurized/Raw
Used on: Dairy
How it’s done: Dairy is not pasteurized before consumption.
Pros: Creamier; advocates claim it’s tastier and more nutritious.
Cons: Raw milk can contain pathogens such as E. coli; spoils quicker; illegal to sell raw dairy in most states; requires refrigeration.

Irradiation
Used on: Meats, wheat, fruits and vegetables, and spices
How it’s done: Foods are exposed to small amounts of gamma rays.
Pros: Kills insects and pathogens, prevents sprouting, and extends shelf life.
Cons: No proof that irradiated foods are safe for human consumption; surviving organisms could help create pathogenic “super strains.”

Cpmment:

Pasteurization

Pasteurization is a process which slows microbial growth in food. The process was named after its creator, French chemist and microbiologist Louis Pasteur. The first pasteurization test was completed by Louis Pasteur and Claude Bernard on April 20, 1862. The process was originally conceived as a way of preventing wine and beer from souring.[1]

Unlike sterilization, inventor Nicolas Appert, pasteurization is not intended to kill all pathogenic micro-organisms in the food or liquid. Instead, pasteurization aims to reduce the number of viable pathogens so they are unlikely to cause disease (assuming the pasteurization product is refrigerated and consumed before its expiration date). Commercial-scale sterilization of food is not common because it adversely affects the taste and quality of the product. Certain food products are processed to achieve the state of commercial sterility.[2]

Pasteurization typically uses temperatures below boiling since at temperatures above the boiling point for milk, casein micelles will irreversibly aggregate (or "curdle"). There are two main types of pasteurization used today: High Temperature/Short Time (HTST) and Extended Shelf Life (ESL) treatment. Ultra-high temperature (UHT or ultra-heat treated) is also used for milk treatment. In the HTST process, milk is forced between metal plates or through pipes heated on the outside by hot water, and is heated to 71.7 °C (161 °F) for 15–20 seconds. UHT processing holds the milk at a temperature of 138 °C (280 °F) for a fraction of a second. ESL milk has a microbial filtration step and lower temperatures than HTST.[3] Milk simply labeled "pasteurized" is usually treated with the HTST method, whereas milk labeled "ultra-pasteurized" or simply "UHT" has been treated with the UHT method.

Pasteurization methods are usually standardized and controlled by national food safety agencies (such as the USDA in the United States and the Food Standards Agency in the United Kingdom). These agencies require milk to be HTST pasteurized in order to qualify for the "pasteurization" label. There are different standards for different dairy products, depending on the fat content and the intended usage. For example, the pasteurization standards for cream differ from the standards for fluid milk, and the standards for pasteurizing cheese are designed to preserve the phosphatase enzyme, which aids in cutting.

The HTST pasteurization standard was designed to achieve a 5-log reduction, killing 99.999% of the number of viable micro-organisms in milk. This is considered adequate for destroying almost all yeasts, mold, and common spoilage bacteria and also to ensure adequate destruction of common pathogenic heat-resistant organisms (including Mycobacterium tuberculosis, which causes tuberculosis and Coxiella burnetii, which causes Q fever). HTST pasteurization processes must be designed so that the milk is heated evenly, and no part of the milk is subject to a shorter time or a lower temperature.

 

 Recent developments

A newer method called flash pasteurization involves shorter exposure to higher temperatures, and is claimed to be better for preserving color and taste in some products.

The term cold pasteurization is used sometimes for the use of ionizing radiation (see Food irradiation) or other means (e.g. chemical) to kill bacteria in food. Food irradiation is also sometimes called pasteurization.

Another means of pasteurization is using pressure called high pressure pasteurization (HPP) [4] also known as High pressure food preservation where extremely high pressure is used to kill the bacteria.

 Products that can be pasteurized

 Pasteurization of milk

Pasteurization is typically associated with milk, first suggested by Franz von Soxhlet in 1886. HTST pasteurized milk typically has a refrigerated shelf life of two to three weeks, whereas ultra pasteurized milk can last much longer when refrigerated, sometimes two to three months. When UHT treatment is combined with sterile handling and container technology (such as aseptic packaging), it can even be stored unrefrigerated for 3–4 months.[citation needed]

A growing body of research supports the belief that pasteurization was not so much a response to any hazards or contamination issues with milk itself, but rather may have been a response to the hazards and contamination issues that resulted from the newly emerging "industrialized" dairy industry. It’s likely that, with the burgeoning growth of large-scale, longer-distance distribution networks, the rise of chain-store supermarkets, and the resulting impetus for larger-herd dairy operations and mechanized milking, there came a corresponding inability to preserve the quality and inherent bacterial-resistance qualities of fresh milk being marketed in a localized area.[5]

 Alternative milk pasteurization standards

Cooling tank

In addition to the standard HTST and UHT standards, there are other lesser-known pasteurization techniques. The first technique, called "batch pasteurization", involves heating large batches of milk to a lower temperature, typically 63 °C (145 °F) for 30 minutes, followed by quick cooling to about 4 °C (39 °F). The other technique is called higher-heat/shorter time (HHST), and it lies somewhere between HTST and UHT in terms of time and temperature. Pasteurization causes some irreversible and some temporary denaturation of the proteins in milk.

In 2001, the Animal and Plant Health Inspection Service of the USDA considered new rules requiring double pasteurization, which would have entailed holding milk at 72 °C (161 °F) for two separate 15-second periods, instead of one 30-second period as was the current standard.

In regions including Africa and South Asian countries, it is common to boil milk to sterilize it after it is harvested. This intense heating greatly changes the flavor of milk, to which the respective people are accustomed.[citation needed]

[edit] Effectiveness of pasteurization

Milk pasteurization has been subject to increasing scrutiny in recent years, due to the discovery of pathogens that are both widespread and heat resistant (able to survive pasteurization in significant numbers).[6] One of these pathogens, Mycobacterium avium subsp. paratuberculosis (MAP), is thought to be a causal agent of Crohn’s Disease.[7] Researchers have developed more sensitive diagnostics, such as real-time PCR and improved culture methods that have enabled them to identify pathogens in pasteurized milk.

Some of the diseases that pasteurization can prevent are tuberculosis, diphtheria, salmonellosis, strep throat, scarlet fever, listeriosis and typhoid fever.

 

 References

  1. ^ Carlisle, Rodney (2004). Scientific American Inventions and Discoveries, p.357. John Wiley & Songs, Inc., new Jersey. ISBN 0471244104.
  2. ^ Montville, T. J., and K. R. Matthews: "food microbiology an introduction", page 30. American Society for Microbiology Press, 2005.
  3. ^ Paving the Way for ESL – extended shelf-life milk products | Dairy Foods | Find Articles at BNET.com
  4. ^ , http://www.defendingfoodsafety.com/tags/high-pressure-pasteurization 
  5. ^ [1] The Untold Story of Milk by Ron Schmid, ND; New Trends Publishing, Nov. 2003
  6. ^ Irene R. Grant et al., "Effect of Commercial-Scale High-Temperature, Short-Time Pasteurization on the Viability of Mycobacterium paratuberculosis in Naturally Infected Cows’ Milk", Applied and Environmental Microbiology, February 2002, p. 602-607, Vol. 68, No. 2
  7. ^ F Autschbach, S Eisold, U Hinz, S Zinser et al., "High prevalence of Mycobacterium avium subspecies paratuberculosis IS900 DNA in gut tissues from individuals with Crohn’s disease", July, 2005, p. 944-949 , Vol. 54
 
 

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