Pasteurization – Definition, Types, Process, Uses

What is Pasteurization?

• Pasteurization is a crucial step in food preservation and plays a vital role in ensuring food safety. Its primary purpose is to destroy disease-causing germs and reduce the number of spoiling organisms present in food. While pasteurization is used in various food and beverage industries, it is most commonly associated with dairy processing.
• The process of pasteurization involves subjecting the food to moderate heat treatment to prevent enzymatic and microbiological deterioration. Heat is applied at temperatures up to 100°C, which effectively eliminates heat-labile spoilage organisms such as non-spore-forming bacteria, yeast, and molds.
• There are two main methods of pasteurization: slow and rapid. Slow pasteurization involves longer exposure to higher temperatures, typically around 75°C for 8 to 10 minutes or 63 to 65°C for 30 minutes. On the other hand, rapid or flash pasteurization requires only a few seconds at temperatures of at least 85 to 90°C. Common combinations include 88°C for one minute, 100°C for 12 seconds, and 121°C for two seconds.
• It is important to note that pasteurization works best when combined with other preservation techniques such as concentration, acidity, and chemical inhibition. This multi-pronged approach enhances the overall effectiveness of the preservation process.
• While pasteurization is an effective method for ensuring food safety, it can be an energy-intensive process due to the high heating and cooling demands. However, it is necessary to eliminate harmful microorganisms and extend the shelf life of perishable foods.
• Louis Pasteur, the French microbiologist, is credited with pioneering the concept of pasteurization in the 1860s. His research demonstrated that thermal processing could deactivate unwanted microorganisms in wine, leading to the widespread adoption of pasteurization in the food industry.
• In addition to traditional pasteurization, there are also non-thermal methods of achieving food safety, such as high-pressure processing (HPP) and pulsed electric field (PEF). These innovative techniques offer alternatives to heat-based pasteurization while still effectively eliminating harmful microorganisms.
• Overall, pasteurization is a critical process in food preservation, enabling the destruction of pathogens and the extension of shelf life while minimizing changes to nutritional quality and sensory characteristics of the treated foods.

Definition of Pasteurization

Pasteurization is a process of treating food and beverages with mild heat to eliminate pathogens and extend shelf life while minimizing changes to nutritional quality and sensory characteristics.

History of Pasteurization 

• The history of pasteurization dates back to the nineteenth century when Louis Pasteur, a French scientist, developed the method. He initially applied pasteurization to wine and beer. In 1862, the high-temperature, short-time (HTST) method was used for the first time.
• During the early 1900s, technological advancements led to the development of various pasteurization techniques. In 1908, Chicago became the first city to pass a law mandating the pasteurization of milk. Vat pasteurization, also known as the holding method, was widely used in the first half of the twentieth century. It involved heating the milk in batches for approximately 30 minutes at around 63 °C.
• By the 1940s, the high-temperature short-time (HTST) continuous method gained significant industrial acceptance. This method involved rapidly heating the milk to high temperatures for a short duration. Over time, different temperature-application times were established to optimize the pasteurization process.
• In modern pasteurization facilities, plate heat exchangers are commonly used to carry out HTST pasteurization. These facilities employ multiple heating and cooling stages to ensure that the milk reaches the appropriate temperatures for pasteurization.

Purpose of Pasteurization

The purpose of pasteurization is to achieve several important objectives in food preservation and safety. While it does not aim to completely eliminate all microbes from food, it effectively reduces the number of live germs, minimizing the risk of disease transmission under proper storage conditions.

Pasteurization plays a significant role as a critical control point (CCP) in many Hazard Analysis and Critical Control Point (HACCP) plans and is widely implemented in the food industry. Its primary purposes can be summarized as follows:

1. Elimination of disease-causing organisms: Pasteurization is commonly employed to eradicate or significantly reduce pathogenic bacteria and other disease-causing microorganisms. For example, pasteurizing milk ensures the destruction of non-spore-forming pathogenic bacteria, reducing the risk of milk-borne illnesses.
2. Reduction of spoilage microorganisms: In addition to pathogens, pasteurization helps to reduce the number of microorganisms that cause food spoilage. By targeting these spoilage organisms, such as bacteria, yeast, and molds, pasteurization slows or halts their growth and enzymatic activity, extending the shelf life of the food product.
3. Preservation of food quality: Pasteurization contributes to maintaining the quality and freshness of various food products. By neutralizing spoilage organisms and enzymes, it helps to prevent undesirable changes in flavor, texture, and appearance, allowing the food to retain its sensory attributes for a longer period.
4. Shelf life extension: Pasteurization, when combined with appropriate storage conditions, enables the extension of food’s shelf life. By reducing the microbial load, it helps to control microbial growth and maintain product quality over a longer period. For example, pasteurized milk can remain safe and consumable for a few days at 4°C or even months for bottled fruits when stored properly.

Overall, the purpose of pasteurization is to enhance food safety, reduce the risk of foodborne illnesses, minimize spoilage, and prolong the shelf life of various food products.

Pasteurization of different foods and their purpose

Pasteurization is applied to various foods to achieve specific purposes depending on the type of food and its characteristics. The pasteurization process for different foods and their main purposes are as follows:

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

In each case, pasteurization serves to eliminate or reduce harmful pathogens and spoilage-causing microorganisms, ensuring food safety and extending the shelf life of the product. The specific temperature and time combinations are determined based on the characteristics of the food and the desired level of microbial inactivation.

Types of Pasteurization

1. Vat Pasteurization or low temperature

Vat pasteurization, also known as batch pasteurization or low-temperature pasteurization, involves the use of a temperature-controlled, closed vat to pasteurize food products. Here are some key points about vat pasteurization:

1. Process: The food product is placed in a vat and heated to a specific temperature, typically between 62°C to 64°C. It is then held at this temperature for a predetermined period, usually around 30 minutes, to ensure proper pasteurization. Afterward, the product is rapidly cooled.
2. Shelf Life: Foods that undergo vat pasteurization typically have a refrigerated shelf life of two to three weeks. The pasteurization process helps to eliminate or reduce harmful microorganisms, extending the product’s freshness and safety.
3. Application: Vat pasteurization is commonly used in the dairy industry for thoroughly pasteurizing milk before it is used to make ice cream, cheese, yogurt, and other dairy products. It ensures the safety and quality of the raw material.
4. Procedure: In vat pasteurization, the raw material is added to the pasteurization vat, heated to the required temperature, and maintained at that temperature for the specified duration. Cooling technology is then employed to rapidly lower the temperature. Finally, the material is pumped out of the vat for further processing or packaging.
5. Usage: While vat pasteurization is primarily associated with smaller businesses and non-milk food products, larger corporations occasionally utilize this method as well. Fruit juices, for example, may undergo vat pasteurization to ensure product safety and extend shelf life.

Advantages of Vat Pasteurization or low temperature

Vat pasteurization, also known as low-temperature pasteurization, offers several advantages for certain food processing applications. Here are the key advantages of vat pasteurization:

1. Suitable for Low-Volume Items: Vat pasteurization is well-suited for low-volume food products in both larger enterprises and small plants. It is a practical option when processing smaller batches of food items, allowing for more precise control over the pasteurization process.
2. Effective for Cultured Products: Vat pasteurization is particularly effective for processing cultured products such as buttermilk and sour cream. These products require specific processing steps like mixing for starter incorporation, incubation for several hours, agitation for breaking the curd, and final cooling. Vat pasteurization accommodates these additional steps alongside the pasteurization and cooling processes.
3. Flexibility in Processing: The use of vats allows for flexibility in processing various food products. Vat pasteurization enables customization of the processing conditions, including temperature, holding time, and agitation, to meet the specific requirements of different food items. This flexibility allows for optimal product quality and consistency.
4. Product Integrity: Vat pasteurization ensures the integrity of the food product, particularly in terms of flavor and texture. The controlled process parameters and gentle heat treatment help to preserve the sensory characteristics and nutritional value of the food items being processed.
5. Equipment Versatility: Vat pasteurization equipment can be designed to accommodate a range of product sizes and shapes. The vats can be tailored to fit specific product volumes, making them versatile for different production needs.
6. Compliance with Regulations: Vat pasteurization allows food processors to comply with food safety regulations and standards. It ensures that the food products meet the required microbial safety standards, reducing the risk of foodborne illnesses and ensuring consumer safety.

Overall, vat pasteurization offers advantages in terms of flexibility, product quality, and compliance with regulations, making it a suitable option for low-volume items and cultured products in various food processing operations.

Disadvantages of Vat Pasteurization or low temperature

Vat pasteurization, or low-temperature pasteurization, has certain disadvantages that should be considered. Here are the key disadvantages of vat pasteurization:

1. Batch Process and Slow Processing: Vat pasteurization is typically carried out in batches, which makes the overall process slower compared to continuous pasteurization methods. Each batch needs to go through the heating, holding, and cooling steps, which can result in longer processing times and reduced production efficiency.
2. Manual Monitoring and Control: Vat pasteurization requires close attention and manual monitoring from operators. They need to ensure that the temperature and holding time are maintained within the specified ranges to achieve proper pasteurization. This manual control increases the risk of human error and requires constant supervision throughout the process.
3. Lack of Heat Regeneration: Vat pasteurization does not have the ability to regenerate heat. As a result, the heating and cooling stages can be relatively expensive in terms of energy consumption. The need for external heating and cooling sources adds to the operational costs of vat pasteurization.
4. Limited Scalability: Vat pasteurization is more suitable for smaller-scale operations due to its batch nature. Scaling up the process to handle larger volumes can be challenging and may require significant investments in equipment and infrastructure.
5. Potential for Overheating or Burning: Since vat pasteurization relies on manual control, there is a risk of overheating or over-holding the product if the operator is not vigilant. This can lead to product quality issues, such as changes in taste, texture, and nutritional content, or even product spoilage.

While vat pasteurization has its drawbacks, it remains a viable option for certain food processing applications, particularly for low-volume and specialty products that require specific processing conditions. However, the limitations in terms of processing speed, manual control, and energy consumption should be considered when evaluating the suitability of vat pasteurization for a particular food production operation.

2. High Temperature/Short Time (HTST) 

High Temperature/Short Time (HTST) pasteurization, also known as flash pasteurization or the continuous method, is a widely used technique for pasteurizing liquid products. Here are the key features and benefits of HTST pasteurization:

1. High Temperature, Short Time: HTST pasteurization involves rapidly heating the liquid to high temperatures for a short duration. The liquid is typically heated to temperatures between 71.5 °C to 76 °C for a period of 15 to 30 seconds. This short exposure to high temperatures is sufficient to destroy harmful bacteria and spores while minimizing the impact on the quality and nutritional content of the product.
2. Continuous Process: HTST pasteurization is a continuous process, meaning that the liquid flows continuously through the pasteurization system. It is well-suited for large-scale production as it allows for a continuous and efficient processing flow, minimizing downtime between batches.
3. Rapid Cooling: After the high-temperature treatment, the liquid is rapidly cooled to between 4 °C and 5.5 °C using a continuous heat exchanger. This rapid cooling helps to preserve the quality and freshness of the product while preventing the growth of bacteria during storage.
4. Effective Microbial Reduction: HTST pasteurization is designed to target harmful bacterial spores, such as Clostridium botulinum spores, as well as other common spoilage and pathogenic microorganisms. It aims to achieve a 5-log reduction, which means reducing the number of live microorganisms in the product by 99.999%.
5. Extended Shelf-Life: HTST pasteurization extends the shelf-life of the pasteurized product. For example, HTST pasteurized milk typically has a refrigerated shelf-life of two to three weeks, allowing for distribution and consumption over a longer period.

HTST pasteurization is widely utilized in the dairy industry and other liquid food processing industries to ensure the safety and quality of products. Its ability to rapidly and effectively destroy harmful microorganisms while maintaining the sensory and nutritional attributes of the product makes it a preferred choice for large-scale pasteurization operations.

Advantages of High Temperature/Short Time (HTST) 

High Temperature/Short Time (HTST) pasteurization offers several advantages in the processing of various food and beverage products:

1. Preservation of Color and Flavor: HTST pasteurization minimizes the impact on the color and flavor of the treated products. The short exposure to high temperatures helps to retain the natural color and flavor profiles, ensuring that the products maintain their desired sensory characteristics.
2. Versatility: HTST pasteurization is suitable for a wide range of food and beverage products. It is commonly used in the pasteurization of milk and dairy products, as well as juice and puree-based goods. Additionally, HTST pasteurization is also applicable to certain beer products, particularly those that are filtered and carbonated.
3. Efficient Process: The continuous nature of HTST pasteurization makes it an efficient process for large-scale production. The continuous flow of the liquid through the pasteurization system allows for a streamlined and uninterrupted operation, reducing downtime between batches and improving overall production efficiency.
4. Microbial Safety: HTST pasteurization is designed to effectively reduce harmful microorganisms, including pathogenic bacteria and spores. By achieving a 5-log reduction in microbial load, HTST pasteurization helps to ensure the safety of the treated products and minimize the risk of foodborne illnesses.
5. Extended Shelf-Life: The microbial reduction achieved through HTST pasteurization extends the shelf-life of the treated products. This enables manufacturers to distribute and market the products over a longer period, reducing potential waste and ensuring product availability for consumers.

Disadvantages of High Temperature/Short Time (HTST) 

While High Temperature/Short Time (HTST) pasteurization offers several advantages, there are also some disadvantages associated with this method:

1. Limited Implementation: The equipment required for HTST pasteurization can be costly to install and maintain. As a result, this approach may be used in fewer manufacturing facilities, especially smaller operations with limited resources or specialized product requirements. Consequently, some food and beverage producers may opt for alternative pasteurization methods that are more feasible for their specific circumstances.
2. Cost Considerations: HTST pasteurization requires sophisticated equipment, including heat exchangers and temperature control systems, to rapidly heat and cool the products. The initial investment and ongoing operational costs associated with such equipment can be significant, making it a relatively expensive process compared to other pasteurization methods. This cost factor may impact the adoption of HTST pasteurization, particularly for businesses with budget constraints or smaller production volumes.
3. Heat Sensitivity: While HTST pasteurization is effective in reducing microbial loads, it may not be suitable for all types of food and beverage products. Some products are sensitive to high temperatures and may undergo undesirable changes in texture, flavor, or nutritional content when subjected to HTST pasteurization. In such cases, alternative pasteurization methods with lower heat exposure or non-thermal techniques may be preferred to preserve the quality of the products.

3. Ultra pasteurization (UP)

Ultra-pasteurization (UP) is a pasteurization method that involves subjecting products to even higher temperatures compared to traditional pasteurization methods. Here are some key points about ultra-pasteurization:

1. Temperature and Time: Similar to high-temperature/short-time (HTST) pasteurization, ultra-pasteurization involves heating the product to a high temperature. However, the specific temperature and duration can vary depending on the product being processed. For example, ice cream, dairy dessert mixes, cream, or processed cheese may require treatments such as heating to 70°C for 25-30 minutes or 80°C for 25 seconds.
2. Extended Shelf Life: Ultra-pasteurization is designed to provide products with a longer shelf life compared to traditional pasteurization methods. By subjecting the product to higher temperatures, ultra-pasteurization aims to eliminate a broader range of microorganisms and enzymes that could cause spoilage. This extended shelf life allows the products to be stored for a longer period, even without the need for continuous refrigeration.
3. Refrigeration Requirement: While ultra-pasteurization can significantly extend the shelf life of products, it is important to note that they still require refrigeration. Although the treatment helps to eliminate many spoilage-causing microorganisms, it may not completely eliminate all microorganisms or enzymes that could lead to spoilage. Therefore, refrigeration is necessary to maintain product quality and prevent microbial growth after ultra-pasteurization.
4. Product-Specific Considerations: The pasteurization process may vary for different dairy products based on their fat content and other characteristics. Manufacturers determine the specific temperature and time parameters for ultra-pasteurization based on the product being processed. This ensures that the treatment is effective in reducing microbial loads and extending the shelf life while maintaining the desired quality attributes of the product.

Ultra-pasteurization provides an effective method for achieving extended shelf life in dairy products and other perishable items. By subjecting products to higher temperatures for a specific duration, ultra-pasteurization can help to enhance food safety and increase the product’s longevity. However, it is essential to balance the benefits of extended shelf life with considerations such as taste, texture, and cost, as some products may undergo changes in sensory attributes with the higher temperatures involved in ultra-pasteurization.

Advantages of Ultra pasteurization (UP)

The advantages of ultra-pasteurization (UP) include:

1. Extended Shelf Life: Ultra-pasteurization significantly extends the shelf life of milk and other dairy products. The process subjects the milk to higher temperatures than traditional pasteurization methods, effectively reducing the microbial load and enzymes that contribute to spoilage. As a result, ultra-pasteurized milk can have a much longer shelf life compared to conventionally pasteurized milk.
2. Improved Food Safety: Ultra-pasteurization helps enhance food safety by eliminating a broader range of microorganisms, including both spoilage-causing organisms and potentially harmful pathogens. The higher temperatures employed during UP ensure a higher level of microbial reduction, providing consumers with a safer product.
3. Convenience and Flexibility: With its extended shelf life, ultra-pasteurized milk offers greater convenience and flexibility to consumers. It can be stored for a longer period without the need for continuous refrigeration, making it suitable for situations where refrigeration may be limited or not readily available. This can be particularly beneficial for consumers who prefer to stock up on milk or for foodservice establishments that require longer storage times.
4. Enhanced Distribution: The extended shelf life of ultra-pasteurized milk enables manufacturers to distribute their products to a broader geographic area. The longer shelf life reduces the risk of spoilage during transportation and allows for increased distribution efficiency.
5. Increased Product Availability: Ultra-pasteurization enables retailers to offer a wider range of dairy products with an extended shelf life. Consumers can access milk and dairy products for a longer duration, reducing the frequency of restocking and ensuring product availability.

Overall, ultra-pasteurization offers significant advantages in terms of extending the shelf life of milk and enhancing food safety. The process provides consumers with greater convenience, flexibility, and access to milk that remains fresh for an extended period.

Disadvantages of Ultra pasteurization (UP)

The disadvantages of ultra-pasteurization (UP) include:

1. Altered Taste: Ultra-pasteurized milk may have a slightly different taste compared to conventionally pasteurized milk. The high temperatures used during UP can affect the flavor profile of the milk, leading to a slightly cooked or “sterilized” taste. Some consumers may find the taste less desirable compared to traditionally pasteurized milk.
2. Nutritional Impact: Ultra-pasteurized milk may have reduced levels of certain vitamins compared to conventionally pasteurized milk. The high temperatures involved in UP can lead to the degradation of heat-sensitive vitamins such as vitamins A, D, and E. As a result, ultra-pasteurized milk may contain lower levels of these vitamins, which are important for overall nutrition.
3. Shorter Shelf Life After Opening: Once a container of ultra-pasteurized milk is opened, its shelf life is typically shorter compared to conventionally pasteurized milk. This is because ultra-pasteurization reduces the levels of antimicrobials, helpful bacteria, and enzymes in the milk. These components play a role in inhibiting the growth of spoilage microorganisms. As a result, once opened, ultra-pasteurized milk may spoil more quickly than conventionally pasteurized milk.
4. Processing Costs: The equipment and processes involved in ultra-pasteurization can be more complex and costly compared to traditional pasteurization methods. The higher temperatures and specialized equipment required for UP can increase production costs for manufacturers. This can potentially lead to higher retail prices for ultra-pasteurized milk compared to conventionally pasteurized milk.
5. Limited Availability: Ultra-pasteurized milk may not be as widely available as conventionally pasteurized milk. Due to the specific processing requirements and costs associated with UP, it may be produced in smaller quantities or offered by a limited number of manufacturers. This limited availability may restrict consumer choice and access to ultra-pasteurized milk in certain regions.

4. Ultra-High-temperature (UHT)

• Ultra-high temperature (UHT) processing, also known as ultra-pasteurization, is a method used to preserve milk and other beverages. It involves heating the milk to a very high temperature of 135°C (275°F) for a short period of time, typically 2-5 seconds. This rapid heat treatment effectively kills harmful bacteria, including their spores, that may be present in the milk.
• After the UHT treatment, the milk is rapidly cooled and then aseptically packaged in sterilized containers. The aseptic packaging ensures that the milk remains free from contamination even when stored at room temperature. UHT milk can be stored for extended periods without the need for refrigeration, typically lasting six to nine months.
• The main advantage of UHT processing is that it provides a significantly longer shelf life compared to conventionally pasteurized milk. This allows for the distribution and availability of milk in areas where refrigeration may be limited or unreliable. UHT milk offers convenience to consumers, as it can be stored without refrigeration until it is opened.
• Furthermore, UHT treatment is expected to eliminate bacterial spores, which are highly resistant forms of bacteria that can cause spoilage and foodborne illnesses. By destroying these spores, UHT processing helps to ensure the safety and quality of the milk.
• However, it is important to note that UHT processing can have some effects on the taste and nutritional content of the milk. The high temperature used during UHT treatment may result in slight changes in flavor, giving UHT milk a different taste compared to fresh or conventionally pasteurized milk. Additionally, some vitamins and nutrients may be slightly reduced due to the heat treatment.
• Overall, UHT processing provides a convenient and effective method for preserving milk, offering an extended shelf life and enhanced safety. Its widespread use has made UHT milk a popular choice in regions where refrigeration is limited or when long-lasting milk is desired.

Advantages of Ultra-High-temperature (UHT)

Ultra-high temperature (UHT) processing offers several advantages compared to conventional pasteurization methods. Some of the key advantages include:

1. Shorter processing times: UHT processing involves heating the product to a very high temperature for a very short period of time, typically 2-5 seconds. This rapid heat treatment allows for quick and efficient sterilization of the product.
2. Longer shelf life: UHT-treated products have significantly extended shelf lives compared to conventionally pasteurized products. The high temperature used during UHT processing helps to eliminate or deactivate harmful bacteria and enzymes that can cause spoilage. As a result, UHT products, such as UHT milk, can be stored at room temperature for months without the need for refrigeration. This provides convenience and flexibility for storage and distribution, particularly in areas with limited refrigeration facilities.
3. Improved product safety: The high temperature achieved during UHT processing ensures the destruction of harmful bacteria, including their spores. This helps to reduce the risk of foodborne illnesses and extends the product’s safety and quality.
4. Aseptic packaging: UHT-treated products are typically packaged using aseptic packaging techniques. This means that the packaging materials and the product itself are sterilized, preventing any recontamination. Aseptic packaging helps to maintain the sterility and quality of the product over a longer period, even without refrigeration.
5. Convenience for consumers: The longer shelf life of UHT products offers convenience to consumers. They can be stored without refrigeration until they are opened, which is particularly useful for households or individuals who may not have access to continuous refrigeration or who prefer to stock up on non-perishable products.

Disadvantages of Ultra-High-temperature (UHT)

Despite the advantages of Ultra-High-Temperature (UHT) processing, there are some disadvantages associated with this method. These include:

1. Reduction in nutritional value: The high temperature and short processing time used in UHT treatment can lead to a reduction in the nutritional value of milk. Heat-sensitive nutrients, such as vitamins and certain enzymes, may be partially degraded during the process, resulting in a decrease in their concentration in the final product. UHT milk may contain lower levels of vitamins A, D, and E compared to conventionally pasteurized milk.
2. Energy consumption: UHT treatment requires significant energy inputs due to the high temperature required for sterilization. The process involves heating the milk to 135°C, which requires a substantial amount of energy to achieve and maintain. This can contribute to higher energy consumption and associated environmental impacts.
3. Flavor changes: The high temperature used in UHT processing can alter the original flavor of milk. Some consumers find that UHT-treated milk has a slightly different taste compared to conventionally pasteurized milk. The flavor change may be more noticeable in sensitive individuals or those accustomed to the taste of fresh milk.
4. Non-biodegradable packaging: UHT milk is typically packaged in cartons or bottles made from materials such as Tetra Pak, which are not biodegradable. These packaging materials can have a significant environmental impact if not properly managed after use. However, it is worth noting that efforts are being made to improve the recyclability and sustainability of UHT milk packaging.

Microorganisms killed by pasteurization

During the pasteurization process, various microorganisms can be killed or inactivated. Some of the microorganisms that are typically targeted and affected by pasteurization include:

1. Acid producers: This group includes bacteria such as Streptococci, Lactobacilli, Microbacteria, Coliforms, and Micrococci, which are responsible for producing acids during fermentation processes. Pasteurization helps eliminate or reduce the population of these acid-producing microorganisms.
2. Gas producers: Certain microorganisms, including Coliforms, Clostridium butyricum, and Torula cremoris, are known for their ability to produce gas during fermentation. Pasteurization helps control and reduce the population of these gas-producing microorganisms.
3. Ropy or stringy fermentation: Some microorganisms, such as Alcaligenes viscolactis and Enterobacter aerogenes, can cause stringy or ropy fermentation, resulting in undesirable texture changes in the product. Pasteurization helps inactivate these microorganisms and prevent ropiness.
4. Proteolytic organisms: Bacillus spp., Pseudomonas spp., Proteus spp., and Streptococcus liquefaciens are examples of microorganisms that possess proteolytic activity, breaking down proteins and potentially leading to spoilage. Pasteurization helps eliminate or reduce the population of these proteolytic organisms.
5. Lipolytic organisms: Microorganisms like Pseudomonas fluorescens, Achromobacter lipolyticum, Candida lipolytica, and Penicillium spp. have the ability to break down lipids or fats, leading to rancidity or off-flavors. Pasteurization helps control and eliminate these lipolytic microorganisms.

Comparison between different pasteurization techniques

When comparing different pasteurization techniques, several criteria can be considered, including process type, temperature and time, foods preserved, shelf life increase, and the microorganisms killed. Here’s a comparison between vat pasteurization, high-temperature/short time (HTST) pasteurization, and ultra-high-temperature (UHT) pasteurization:

1. Process type:
   • Vat pasteurization: It is a batch process where the food is heated in a closed vat.
   • HTST pasteurization: It is a continuous process where the food is rapidly heated and then cooled using a continuous heat exchanger.
   • UHT pasteurization: It is also a continuous process where the food is heated to ultra-high temperatures and aseptically packaged.
2. Temperature and time:
   • Vat pasteurization: Typically conducted at 65°C for 30 minutes.
   • HTST pasteurization: Usually performed at temperatures around 72°C for 15 to 30 seconds.
   • UHT pasteurization: Involves temperatures ranging from 135°C to 150°C for just a few seconds.
3. Foods preserved:
   • Vat pasteurization: Commonly used for preserving buttermilk and sour cream.
   • HTST pasteurization: Suitable for a variety of foods including milk, eggnog, frozen dessert mixes, fruit juices, and more.
   • UHT pasteurization: Primarily used for preserving milk.
4. Shelf life increase (milk):
   • Vat pasteurization: Extends the shelf life of milk by several days when refrigerated.
   • HTST pasteurization: Increases the shelf life of milk to approximately 2 to 3 weeks when refrigerated.
   • UHT pasteurization: Provides a much longer shelf life for milk, ranging from 6 to 9 months when aseptically packaged.
5. Microbes killed:
   • Vat pasteurization: Targets vegetative pathogens, reducing their population.
   • HTST pasteurization: Aims to eliminate vegetative pathogens present in the food.
   • UHT pasteurization: Designed to kill or inactivate all bacteria and spores present, ensuring a high level of microbial safety.

Each pasteurization technique has its advantages and suitability for specific food products, with varying impacts on shelf life and microbial control. Choosing the most appropriate technique depends on factors such as the type of food, desired shelf life, and the level of microbial safety required.

FAQ

References

1. Challis, C., Wilson, R. E., Kay, T., Tierney, M., & Todd, A. (2018). A review of pasteurisation process monitoring to support energy efficiency in the dairy industry. Eceee Industrial Summer Study Proceedings, 2018-June, 379–388.
2. Bousbia, A., Gueroui, Y., Boudalia, S., Benada, M., & Chemmam, M. (2021). Effect of High Temperature, Short Time (HTST) Pasteurization on Milk Quality Intended for Consumption. Asian Journal of Dairy and Food Research, 40(2), 147–151. https://doi.org/10.18805/ajdfr.DR-210
3. Chiozzi, V., Agriopoulou, S., & Varzakas, T. (2022). Advances, Applications, and Comparison of Thermal (Pasteurization, Sterilization, and Aseptic Packaging) against Non-Thermal (Ultrasounds, UV Radiation, Ozonation, High Hydrostatic Pressure) Technologies in Food Processing. Applied Sciences 2022, Vol. 12, Page 2202, 12(4), 2202. https://doi.org/10.3390/APP12042202
4. Cifelli, C. J., Maples, I. S., & Miller, G. D. (2010). Pasteurization: Implications for food safety and nutrition. Nutrition Today, 45(5), 207–213. https://doi.org/10.1097/NT.0b013e3181f1d689
5. Datta, N., Elliott, A. J., Perkins, M. L., & Deeth, H. C. (2002). Ultra-high-temperature (UHT) treatment of milk: Comparison of direct and indirect modes of heating. Australian Journal of Dairy Technology, 57(3), 211–227.
6. Edition, T. (2008). Food microbilogy. In Food Microbiology. https://doi.org/10.1039/9781847557940-00182
7. Fay, D. L. (1967). modern indutrial microbiology and botechnology. In Angewandte Chemie International Edition, 6(11), 951–952.
8. Fernandes, R. (2009). MICROBIOLOGY HANDBOOK DAIRY PRODUCTS. http://www.leatherheadfood.com
9. Motarjemi Y, Lelieveld H (2014). Food Safety Management : A practical guide for the food industry. Elsevier Inc.
10. Modi A, & Prajapat R. (2014). Pasteurization Process Energy Optimization For A Milk Dairy Plant By Energy Audit Approach. INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH, 3(6). www.ijstr.org
11. Patel. (2013). Advances in Dairy Research. Adv Dairy Res, 9, 2021.
12. Sarkar, S. (2015). Microbiological Considerations: Pasteurized Milk. International Journal of Dairy Science, 10(5), 206–218. https://doi.org/10.3923/ijds.2015.206.218