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What is Pasteurization and Homogenization

Pasteurization is the process of heating liquids for the purpose of destroying bacteria, protozoa, molds, and yeasts, whereas Homogenization is a term connoting a process that makes a mixture the same throughout the entire substance.

What is Pasteurization?

Pasteurization is the process of heating liquids for the purpose of destroying bacteria, protozoa, molds, and yeasts. The process was named after its creator Louis Pasteur. The first pasteurization test was completed by Pasteur and Claude Bernard on April 20, 1862.

Unlike sterilization, pasteurization is not intended to kill all micro-organisms (pathogenic) in the food or liquid. Instead, pasteurization aims to achieve a "logarithmic reduction" in the number of viable organisms, reducing their number so they are unlikely to cause disease.

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 Deg C (161 Deg F) for 15-20 seconds.

UHT processing holds the milk at a temperature of 138 Deg C (250 Deg F) for a fraction of a second. ESL milk has a microbial filtration step and lower temperatures than HTST.

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 is typically associated with milk.

HTST pasteurized milk 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.

Pasteurization causes some irreversible and some temporary denaturation of the proteins in milk.

Milk pasteurization has been subject to increasing scrutiny in recent years, due to the discovery of pathogens that are both widespread and heat resistant. 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, polio, salmonella, strep throat, scarlet fever, and typhoid fever.

What is Homogenization?

Homogenization (or homogenisation) is a term used in many fields such as chemistry, agricultural science, food technology, sociology and cell biology. Homogenization is a term connoting a process that makes a mixture the same throughout the entire substance.

Homogenization is a process that involves breaking apart cells - releasing organelles and cytoplasm. When the purpose is to extract organelles, it is frequently done in two steps; first using a blender to break the tissue up, and then with an ultrasonic or mechanical tissue disruptor. The organelles are then generally separated using differential centrifugation. Depending upon the subcellular fraction wanted, different processes are used to separate them. When the aim is to extract nucleic acids, the tissue is often ground in a mortar and pestle under liquid nitrogen.

Sometimes, however, a much milder procedure is followed, where the aim is to collect whole, intact cells. Homogenized cells must be kept at low temperatures to prevent autolysis and kept in an isotonic solution to prevent osmotic damage.

One of the oldest applications of homogenization is in milk processing, where the aim is to prevent or delay the natural separation of cream from the rest of the emulsion. The fat in milk normally separates from the water and collects at the top. Homogenization is the process of breaking up that fat into smaller sizes so that it no longer separates from the milk, allowing the sale of non-separating 2% and whole milk. This is accomplished by forcing the milk at high pressure through small orifices.

When soft solids are milled in a liquid, this can also be seen as a form of homogenization.


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