Key Takeaways
- Blanching: Uses brief heat treatment to inactivate enzymes in fruits and vegetables before further processing, such as freezing or canning.
- Pasteurization: Applies controlled heat to reduce targeted pathogens and spoilage microorganisms in products such as milk and fruit juices.
- Commercial Sterilization: Uses validated heat treatments to achieve the microbial control required for shelf-stable foods.
- Temperature and Time: The correct combination of processing temperature and duration is essential for food safety, quality, and shelf life.
- Advantages: Thermal processing can improve food safety, extend shelf life, reduce food waste, and support large-scale production.
- Limitations: Excessive heat can affect nutrients, flavour, and texture while increasing energy consumption and equipment costs.
- Equipment Selection: Food manufacturers should consider product composition, acidity, microbial risks, packaging, and storage conditions when selecting thermal processing equipment.
Introduction
Thermal methods of food preservation use controlled heat energy to destroy or inactivate spoilage microorganisms, enzymes and foodborne pathogens responsible for food deterioration. Food manufacturers can adjust the temperature and processing time to extend the shelf life. It can also improve food safety and maintain product quality.
These methods are used across the dairy, beverage, meat, seafood, fruit, and vegetable processing industries. The three thermal methods used for food preservation are blanching, pasteurization, and commercial sterilization. Each technique is used for different purposes based on the food’s acidity, composition, microbial risks and storage conditions.
Core Principles of Thermal Food Preservation
Effective thermal processing preservation can depend on three main factors.
1. Temperature
Heat causes damage to the proteins of micro-organisms. Their cell membranes and other structures are essential for their survival. The higher the temperature, the faster microbial inactivation takes place.
2. Processing Time
The time taken for processing is determined by how long the food is exposed to heat, and it affects both the destruction of microorganisms and the inactivation of enzymes. The amount of time required will vary as per the temperature and type of food being processed.
3. Food Composition and pH
The food composition and its pH level affect microbial growth and heat resistance. Low-acid foods, especially with a pH higher than 4.6, require special consideration because they can allow the growth of hazardous spore-forming bacteria such as Clostridium botulinum.
Three Primary Types of Thermal Food Preservation
Here are the main thermal methods of food preservation
1. Blanching
Blanching is a brief heat treatment that is used for preparing fruits and vegetables. In this method, the food is subjected to hot water or steam for a specific duration and is then quickly cooled.
Process
- Clean and get the fruits or vegetables ready.
- Put them in hot water or steam at the appropriate temperature.
- Continue with the treatment for the specified period, as per the size and product.
- To prevent the food from continuing to cook, it should be cooled quickly.
The process of blanching can deactivate the enzymes which cause unwanted changes in colour, taste, texture, and nutritional value during storage. It can decrease the number of microorganisms on the surface and get rid of the air that is trapped in the plant tissues.
Applications
This method is usually applied to leafy greens, peas, carrots, green beans, and other vegetables before freezing or canning. Some fruits are also blanched before they are dried or peeled.
Note that blanching is not a full preservation method. Food that has been blanched usually needs further processing by freezing, drying, or canning, if it is to have the required shelf life.
2. Pasteurization
Pasteurization is another method for food preservation. It uses controlled heat to destroy the targeted disease-causing microorganisms and reduce spoilage organisms. It is less intensive than commercial sterilization and retains the food’s original flavor and nutritional characteristics.
The common pasteurization schedules for milk consist of the following:
- Low-Temperature Long-Time (LTLT): Approximately 63°C for 30 minutes.
- High-Temperature Short-Time (HTST): Approximately 72°C for 15 seconds.
These are the established milk pasteurization schedules, but some other foods may require different conditions based on their properties and safety requirements.
Process
The food is heated to the specific temperature, held for the specific period and cooled when required. Industrial systems use plate heat exchangers to heat and cool liquid products effectively.
Applications
This method is used for milk, liquid egg products, cream, fruit juices and some beverages. It can improve food safety and extend the refrigerated shelf life.
3. Commercial Sterilization
Commercial sterilization consists of applying the validated heat treatment to food to control the microorganisms that may cause spoilage or health risks. It is widely used for low-acid packaged foods.
Processing temperatures may range from 110°C to 130°C or higher, based on the packaging, product, equipment, and required treatment.
Process
- Follow the product formulation when preparing the food.
- Put it into appropriate containers, for example, cans or retort pouches, when using in-container processing.
- Ensure that the containers are completely sealed.
- Perform the heat treatment which has been validated in a pressure vessel known as a retort.
Place the containers under controlled conditions and then check the package integrity.
It is important to achieve the required level of microbial control in many low-acid foods for the processing temperature to go above the boiling point of water. This can be achieved by applying pressure. The use of commercial sterilization includes canned meats, poultry, fish, vegetables, soups, and shelf-stable ready-to-eat meals.
It does not follow that all viable microorganisms are eliminated by commercial sterilization. Instead, it can achieve the degree of microbial control needed for the food’s proposed storage and distribution conditions.
Advantages of Thermal Food Preservation
There are various advantages of thermal methods of food preservation for food manufacturers and consumers.
1. Improved Food Safety
The heat treatments to food can reduce the targeted pathogens and spoilage microorganisms.
2. Extended Shelf Life
Thermal preservation methods such as UHT processing and commercial sterilization can make food products shelf-stable.
3. Reduced Reliance on Preservatives
Heat treatment can achieve preservation without requiring synthetic preservative additives, even when other ingredients may be used.
4. Large-Scale Production
Preserving food by heat treatment can support consistent processing and distribution across wider markets.
5. Reduced Food Waste
It can increase the shelf life of food and help manufacturers, retailers, and consumers control food waste.
Disadvantages of Thermal Food Preservation
Although it has some advantages, thermal processing does have certain limitations. Here are its disadvantages
1. Loss of Nutrients
Vitamin C and thiamine, which are sensitive to heat, can be reduced based on the processing conditions.
2. Changes in Taste and Texture
Intense heating can lead to browning, softening, denaturation of proteins, and changes in flavour.
3. Use of Energy
Energy is needed for heating, cooling and steam generation, which can increase operating costs and environmental impacts.
4. Equipment Investment
There is an investment needed for industrial pasteurizers, retorts, and aseptic packaging systems, along with the costs of maintenance and the need for skilled operation.
Manufacturers may overcome these difficulties by improving heat recovery, optimizing the combination of time and temperature, and using the appropriate processing equipment.
Reliable Thermal Processing Solutions from Envitro Technomech
Envitro Technomech supports the food manufacturers to maintain the consistent heat treatment and achieve the food safety standards, product quality, and shelf life. Whether your food production consists of cooking, heating, pasteurization, or other Food Processing Machinery, you must choose the right equipment that fits your product and meets your requirements. Contact Envitro Technomech to discuss your equipment solutions for the food processing business.
Conclusion
Thermal methods of food preservation are important to improve food safety, increase shelf life and control spoilage. One of the popular thermal preservation methods is blanching, which is used to inactivate enzymes. Pasteurization works to reduce specific pathogens, and commercial sterilization allows specific foods to stay shelf-stable.
Other preservation methods available are UHT, retort processing and aseptic processing, which are suitable for particular products and packaging systems. When choosing the right method, you must consider the food acidity, its composition, microbial risks and storage requirements.
Also Read: Difference Between CAPEX and OPEX in Food Processing Plants
FAQs
Q1. What Are Thermal Methods of Food Preservation?
The thermal methods for food preservation use controlled heat to destroy the targeted microorganisms, inactivate enzymes and reduce spoilage. They can extend the food shelf life and maintain the quality and safety.
Q2. What Are the Three Main Thermal Preservation Methods?
The three popular thermal preservation methods are blanching, pasteurization, and commercial sterilization. Each method uses different heat conditions to control microorganisms or enzymes as per the specific preservation requirements.
Q3. What Is the Difference Between Sterilization and Pasteurization?
Sterilization can achieve greater microbial control for suitable shelf-stable foods stored without refrigeration. On the other hand, pasteurization can reduce the targeted pathogens and spoilage microorganisms.
Q4. Which Foods Undergo Thermal Preservation?
Vegetables, milk, fruit juices, seafood and ready-to-eat meals undergo thermal processing through blanching, pasteurization, canning, sterilization, or UHT treatment.
Q5. What Are the Disadvantages of Thermal Food Preservation?
Thermal processing can reduce heat-sensitive vitamins, change texture and flavor, consume substantial energy and require specialized equipment and validated procedures for consistent food safety.