Pasteurization: Definition, Types, Process, Comparison, and Uses

• One of the most important steps in preservation and a need for food safety is pasteurisation.
• Pasteurisation is required to eliminate pathogenic microbes and considerably reduce organisms that cause food to deteriorate. 
• The most common use of pasteurisation is in the dairy processing sector of the food and beverage industry. 
• Milk is a popular product for which pasteurisation is applied worldwide.
• To stop enzymatic and microbiological degradation, it is referred to as "moderate heat treatment". 
• Heat-labile spoilage organisms such non-spore-forming bacteria, yeast, and moulds are removed by heating food to up to 100°C.
• Pasteurisation is frequently an energy-demanding procedure because of the high amounts of heating and cooling requirements.
• Other preservation methods including concentration, acidity, and chemical inhibition complement pasteurisation the best.
• In pasteurizing, two processes can be used: slow and rapid.
• Slow pasteurisation employs higher temperatures for a longer period of time; common temperature-time combinations are 75°C for 8 to 10 minutes or 63 to 65°C for 30 minutes.
• At pasteurisation temperatures of at least 85 to 90°C, rapid, high, or flash pasteurisation only takes a few seconds. There are several typical combinations of temperature and time, such as 88°C (190°F) for one minute, 100°C for 12 seconds, and 121°C for two seconds.

Table of Contents

• Pasteurization History
• Purpose of Pasteurization
• Pasteurization of different foods and their purpose
• Types of Pasteurization
• 1. Vat Pasteurization or low temperature
• 2. High Temperature/Short Time (HTST) 
• 3. Ultra pasteurization (UP)
• 4. Ultra-High-temperature (UHT)
• Microorganisms killed by pasteurization
• Comparison between different pasteurization techniques

Pasteurization History

• Pasteurisation was created in the nineteenth century by a French scientist named Louis Pasteur. He used this approach to both wine and beer. 
• For the first time, a high-temperature, short-time (HTST) approach was applied in this operation in 1862. 
• Technology advanced quickly in the early 1900s, spurring the creation of several pasteurisation methods. 
• In 1908, Chicago became the first city to enact legislation mandating milk pasteurisation. 
• In the early part of the 20th century, technology was dominated by the holding technique, also known as vat pasteurisation. The milk is batch heated using this manner for 30 minutes at around 63 °C. 
• High temperature short-time (HTST) continuous techniques, however, had already attained general industrial adoption by the early 1940s. 
• There were a number of temperature-application timings released as the procedure's technology developed.
• Nowadays, the widely used HTST method of pasteurising milk is usually carried out using plate heat exchangers.
• The multiple heating and cooling processes used in a modern pasteurisation plant make sure the milk reaches the right temperatures. 

Purpose of Pasteurization

• Pasteurisation does not seek to eliminate all microorganisms from food. Instead, if the right conditions are applied to storage settings, it helps to minimise the quantity of living germs, making them less likely to cause disease. 
• The food industry frequently uses it as a CCP and many HACCP programmes do as well. 
• In most cases, pasteurisation is used to completely destroy all disease-causing organisms (as in the pasteurisation of milk) or to drastically reduce the quantity of organisms that cause food to deteriorate (as in the pasteurisation of vinegar). 
• All non-spore-forming pathogenic bacteria, the majority of vegetative spoiling microorganisms, and the activity of microbes and enzymes are neutralised by pasteurisation. 
• Low temperatures, typically 4°C for a few days (for example, milk) or months (for example, bottled fruit), enhance the shelf life of food.

Pasteurization of different foods and their purpose

S.N.	Food	Main Purpose	Sub-purpose	Conditions of processing
1	Fruit juice (pH < 4.5)	Enzyme inactivation (pectinesterase, polygalacturonase)	Destruction of spoilage-causing microorganisms (Salmonella enterica, Cryptosporidium parvum)	65°C for 30 min; 77°C for 1 min; 88°C for 15 s
2.	Beer (pH < 4.5)	Destruction of spoilage-causing microorganisms (wild yeasts, Lactobacillus species) and (residual yeasts, Saccharomyces species)	Destruction of spoilage-causing microorganisms	65°C–68°C for 20 min (in bottle); 72°C–75°Cfor 1–4 min at 900–1000 kPa
3.	Milk (pH > 4.5)	Destruction of pathogens:Brucella abortus, Mycobacterium tuberculosis, Coxiella burnetti	Destruction of spoilage-causing microorganisms (Streptococcus laptis, Streptococcus cremoris) and enzymes	63°C for 30 min; 71.5°C for 15 s
4.	Liquid egg	Destruction of pathogens (Salmonella seftenburg)	Destruction of spoilage microorganisms	64.4°C for 2.5 min; 60°C for 3.5 min
5.	Ice cream	Destruction of spoilage microorganisms.	Destruction of pathogens	65°C for 30 min; 71°C for 10 min; 80°C for 25 s

Types of Pasteurization

1. Vat Pasteurization or low temperature

• A closed, temperature-controlled vat makes up a pasteurizer.
• It is sometimes referred to as batch pasteurisation, low-temperature pasteurisation, or protracted pasteurisation. 
• The food item is quickly cooled after being heated to a temperature of between 62 and 64 °C and held there for around 30 minutes. 
• In a refrigerator, pasteurised food has a two- to three-week shelf life.
• The raw material is put into the pasteurisation vat, heated to the necessary temperature, maintained for the necessary amount of time, cooled off, and then pumped out of the vat. 
• Before manufacturing ice cream, cheese, yoghurt, and other common food products, milk is fully pasteurised in vats in the dairy industry. 
• The major applications for vat/batch pasteurisation nowadays are smaller firms and products other than milk. 
• However, large corporations do use it occasionally (for example, fruit juices).  

Advantages

1. In both larger businesses and smaller operations, vat pasteurisation is useful for low-volume commodities. 
2. They work particularly well when processing cultured foods like buttermilk and sour cream, which need to be pasteurised, cooled, and mixed to incorporate the starter before being held quietly for several hours to break the curd and finish cooling the tank. 

Disadvantages

1. Vat pasteurisation is sluggish since it frequently happens in batches. 
2. Despite using manual controls, the operator must constantly exercise caution to prevent overheating, overholding, and burning. 
3. Heating and cooling are relatively costly since the vat cannot renew heat. 

Product	Temperature	Time
Milk	62 °C	30 minutes
Cream, yogurt	65 °C	30 minutes
Eggnog, frozen dessert mixes	69 °C	30 minutes
Table: Vat pasteurization temperature and time for food products

2. High Temperature/Short Time (HTST) 

• The continuous process or flash pasteurisation are other names for HTST pasteurisation.
• Pasteurisation using a high temperature for a brief period of time is known as HTST. 
• One of the most often used pasteurisation methods at the moment. 
• Using a continuous heat exchanger, the liquid is first quickly heated to temperatures between 71.5 °C and 74 °C for around 15 to 30 seconds, or between 74 °C and 76 °C for 15 to 20 seconds. 
• It targets resistant Clostridium botulinum spores, which are dangerous bacterial spores. 
• For HTST pasteurised milk, a typical refrigerated shelf-life is two to three weeks. 
• By achieving a 5-log reduction in the amount of living microorganisms in milk, the HTST pasteurisation should almost eradicate all yeasts, mould, common spoilage, and dangerous bacteria. 

Advantages

1. Better colour and flavour preservation. 
2. Milk products, juice/puree-based products, and even beer products are all suitable.

Disadvantages

1. This approach can be used in fewer manufacturing facilities. 
2. It is pretty expensive.

3. Ultra pasteurization (UP)

• Ultra-pasteurization is likewise done at a higher temperature and with somewhat different equipment than the HTST process. 
• Although UP pasteurised items have a longer shelf life, refrigeration is still necessary.
• Depending on the amount of fat in the product, different dairy products require different pasteurisation techniques. 
• Stronger treatments, such as 70°C for 25–30 minutes or 80°C for 25 seconds, are required for ice cream, dairy dessert mixtures, cream, or processed cheese.

Advantages  

1. Ultrapasteurization significantly extends the shelf life of milk. 

Disadvantages

1. Compared to regular pasteurised milk, the milk has a different flavour and has up to 20% less vitamins A, D, and E.
2. Pasteurised milk has a reduced shelf life after opening due to lower quantities of antimicrobials, beneficial microorganisms, and enzymes. 

4. Ultra-High-temperature (UHT)

• Milk preservation now uses ultra-high temperature (UHT). 
• The milk is packaged and aseptically placed into containers after being sterilised at 135°C for 2–5 seconds. 
• UHT milk can occasionally survive six to nine months without being refrigerated.
• Bacterial spores should also be eliminated by UHT therapy. 

Advantages

1. Its processing times are quicker. 
2. The shelf life are longer. 

Disadvantages

1. Milk Loses Nutritional Value Due to Sterilisation 
2. UHT Treatment is quite energy-intensive. 
3. The UHT Process alters the milk's natural flavour. 
4. Packaging for UHT milk is not biodegradable. 

Microorganisms killed by pasteurization

• Streptococci, Lactobacilli, Microbacteria, Coliforms, and Micrococci are acid-producing organisms. 
• Coliforms, Clostridium butyricum, and Torula cremoris are gas generators. 
• Fermentation that is ropy or stringy: Alcaligenes viscolactis, Enterobacter aerogenes
• Streptococcus liquefaciens, Pseudomonas spp., Bacillus spp., Proteus spp., and other proteolytic organisms
• Pseudomonas fluorescens, Achromobactor lipolyticum, Candida lipolytica, and Penicillium spp. are examples of lipolytic organisms.

Comparison between different pasteurization techniques

Criteria	VAT	HTST	UHT
Process type	Batch	Continuous	Continuous
temperature and time	65 °C for 30 min	72 °C for 15–30 s	135–150 °C for a few seconds
Foods preserved	Buttermilk and sour cream	Milk, eggnog, frozen dessert mixes, fruit juices, etc.	Milk
Shelf life increase (milk)	Several days when refrigerated	2–3 weeks when refrigerated	6–9 months when aseptically packaged
Microbes killed	Vegetative pathogens	Vegetative pathogens	All bacteria and spores