Key Difference – HTST vs UHT Pasteurization Techniques
Pasteurization is defined as partial sterilization of a substance and especially a liquid (as milk) at a temperature and for a period of exposure that destroys objectionable organisms without major chemical alteration of the substance. It was invented by Louis Pasteur. In HTST Pasteurization, the product is subjected to much lower temperature (71.7°C, almost half of the temperature which is used for UHT method) over a long period (15 seconds) compared to UHT Pasteurization. This is the key difference between HTST and UHT pasteurization techniques and further differences are described in this article.
What is HTST Pasteurization Technique?
HTST is the most common pasteurization technique in the dairy industry. HTST stands for High Temperature, Short Time. It is also known as flash pasteurization. It is a method of pasteurizing perishable beverages like fruit and vegetable juices, beer, kosher and wine. Pasteurization makes the product safe for consumption and extends the shelf life compared to unpasteurized products. It removes spoilage microorganisms. This was first introduced in 1993 and observed 99.99% reduction of harmful bacteria. This is a faster and energy efficient method, and it maintains the color and flavor of most products.
According to the US standard protocol for milk pasteurization, milk is subjected 71.7°C (161 °F) for about 15 seconds in order to kill Coxiella burnetii (the most heat resistant pathogen found in raw milk). It also kills most pathogenic bacteria like Salmonella, E.coli, and Listeria.
Basic Steps of HTST Pasteurization of Milk
- Cold raw milk is fed into the pasteurization plant
- The milk passes into the regenerative heating section of the plate heat exchanger.
- In the regenerating section, cold milk is pumped through the A chambers (odd numbered chambers in series of chambers) while milk that has already been heated and pasteurized is pump through the B chambers (even numbered chambers).
- The heat from hot milk passes into the cold milk through steel plates. This warms the milk to 57 – 68 °C (134.6-154.4 °F)
- Next, milk passes to the heating section of the plate heat exchanger. Hot water in B chamber heats the milk to around 72 °C (71.7°C).
- Then it passes through the holding tube and takes 15 seconds to complete the passage by fulfilling the time requirement of HTST pasteurization.
- After that, it is re-sent to the regenerative section where milk is again cool to 32 °C.
- Then the cooling section of the plate heat exchanger uses coolant or cold water to bring the temperature of pasteurized milk to 4 °C.
What is UHT Pasteurization Technique?
UHT Pasteurization is also known as Ultra-High-Temperature (UHT) Pasteurization. This typically involves heating milk or cream to 140 °C (284 °F) for 4 seconds. The milk is packaged in sterile hermetically-sealed containers. Therefore, it can be stored for up to 90 days without refrigerating conditions. UHT is commonly used in milk pasteurization but is also can be used for fruit juices, cream, soy milk, yogurt, wine, soups, honey, and stews. UHT milk was first used in 1960.
Basic Steps of UHT Pasteurization
- Spraying the milk or juice through the nozzles into a chamber filled high-temperature steam under pressure
- After temperature reaches to 140 °C, the fluid is instantly cooled in a vacuum chamber
- Packed in pre-sterilized containers
What is the difference between HTST and UHT Pasteurization Techniques?
Features of HTST and UHT Pasturization Techniques:
Temperature:
HTST pasteurization: HTST pasteurization has a much lower temperature. (71.7 °C)
UHT pasteurization: UHT pasteurization has a comparatively higher temperature. (140°C)
Duration:
HTST pasteurization: HTST pasteurization takes much longer duration with compared to UHT pasteurization.
UHT pasteurization: UHT pasteurization takes only seconds.
Shelf-Life:
HTST pasteurization: HTST pasteurization provides lower shelf life period (2-3 weeks)
UHT pasteurization: UHT pasteurization provides longer shelf life period (2-3months)
Damage:
HTST pasteurization: HTST pasteurization causes minimal damage to the nutritional value of the food.
UHT pasteurization: UHT pasteurization basically kills most of its nutritional value.
Technique:
HTST pasteurization: HTST pasteurization is basically a pasteurization technique
UHT pasteurization: UHT pasteurization is a pasteurization technique as well as a sterilization technique.
Color and flavor:
HTST pasteurization: HTST technique preserves the color and flavor of the food. It does not cause Millard browning.
UHT pasteurization: UHT technique does not preserve the color and flavor as it causes Millar browning.
Protein denaturation:
HTST pasteurization: HTST technique does not cause protein denaturation
UHT pasteurization: UHT pasteurization causes structural damages to the protein structure thereby causing it to elongate.
Sterilization:
HTST pasteurization: HTST pasteurization kills many pathogenic bacteria, but it still remains some nonpathogenic bacteria which can cause milk spoilage
UHT pasteurization: UHT pasteurization kills all bacteria in the milk.
Process of introducing milk to the plant:
HTST pasteurization: In HTST, milk is fed into the plant.
UHT pasteurization: In UHT technique milk is sprayed into the chamber through nozzles.
References:
Flash pasteurization [Online]. Available: https://en.wikipedia.org/wiki/Flash_pasteurization [Accessed June 30 2016].
Pasteurization [Online]. Available: https://en.wikipedia.org/wiki/Pasteurization.
PASTEURIZED VS ULTRA-PASTEURIZED [Online]. Available: http://www.jolynneshane.com/what-is-the-difference-between-pasteurized-and-ultra-pasteurized.html [Accessed June 30 2016].
Pasteurization [Online]. Available: http://www.idfa.org/news-views/media-kits/milk/pasteurization.
HAAS., R. 2015. Loss of Nutritional Value in Ultra-Pasteurized Vs. Pasteurized Milk [Online]. Available: http://www.livestrong.com/article/507949-loss-of-nutritional-value-in-ultra-pasteurized-vs-pasteurized-milk/ [Accessed July 01 2016].
WHITE., C. How Pasteurization Works [Online]. Available: http://science.howstuffworks.com/life/cellular-microscopic/pasteurization4.htm [Accessed June 30 2016].
Image Courtesy:
“Whole milk UHT” By khrawlings – whole milk UHT (CC BY 2.0) via Commons Wikimedia
“Simple Pasteurization” By Emma – Own work (CC BY-SA 4.0) via Commons Wikimedia