This article explores innovative food refrigeration technologies transforming food processing: vacuum cooling, ultrasonic assistance, high-pressure freezing, and antifreeze proteins. Vacuum cooling accelerates chilling by evaporating water in a low-pressure environment, enhancing food safety and quality. Ultrasonic assistance uses high-frequency sound waves to optimize freezing, producing smaller ice crystals for better texture and quality. High-pressure freezing applies intense pressure and low temperatures for rapid freezing, preserving food structure. Antifreeze proteins help control ice crystal growth, maintaining texture in frozen foods. These advancements improve food refrigeration techniques like preservation, quality, and efficiency, meeting evolving industry needs and consumer expectations.
1. Vacuum Cooling of Foods
1.1 Introduction
Vacuum cooling is a food refrigeration technique that reduces the pressure in the chamber’s food environment, allowing water to evaporate from food and rapid freezing.
1.2 Vacuum Cooling Principles, Process, and Equipment
The vacuum cooling principle is based on the following: Water is boiling at a low temperature under less pressure. The pressure in the vacuums for the product is reduced, and water starts to evaporate, absorbs heat, and leads to quick cooling. Vacuum cooling minimizes the pressure on food products, which leads to water evaporating from food. It is a rapid chilling process in which the evaporation cools down the product rapidly by absorbing heat. The vacuum cooling process includes loading food products, either harvested or cooked food, inside the vacuum.
The chamber is sealed in an airtight container, and pressure decreases for water evaporation. The evaporation of water and the cooling process in food leads to a temperature drop. The process is continued until it is complete. Then, the product is removed from the chamber.
Equipements that are used in the process of vacuum cooling:
- Vacuum pump
- Vacuum chamber
- Cooling system
- Control system
- Condenser
1.3 Application of Vacuum Cooling in the Food Industry
Vacuum cooling is used in the food industry to treat cooked foods to maintain safety and quality.
- Flowers are also treated with vacuum cooling to increase shelf life, and bakery items are cooled for enhanced texture and quality.
- If herbs like cilantro and basil are cooled, it results in an extended shelf-life product.
- Berries are rapidly cooled to prevent mold growth and retain texture. It is also used to treat mushrooms.
- This cooling process is used in the food industry to treat meat and poultry, either for processing or cooked meat. Cooked meat includes roast chicken, beef, and turkey.
- Seafood like shellfish and fish is cooled rapidly to prevent spoilage and increase shelf life. Ready-to-eat meals and salads are also treated with vacuum cooling.
- Food restaurants like kitchens or catering service providers use this process for large amounts of food treatment.
1.4 Mathematical Modelling of the Vacuum Cooling Process
The food industry should have complete knowledge of fluid dynamics and thermodynamics for the mathematical modeling of vacuum cooling.
Implementing model: Conditions like humidity, pressure, and temperature should be maintained in a way relevant to food and its environment.
Numerics: The standard equation methods are finite element, finite volume, and finite difference methods.
Calibration: Data should be calibrated for accuracy in mathematical modelling.
1.5 Advantages and Disadvantages of Vacuum Cooling
(i.) Advantages
- Vacuum cooling reduces cooling time compared to conventional methods and efficiently minimizes bacterial growth risk and spoilage.
- The cooling process provides a uniform treatment of cooling the food for the desired end product. Consistency enhances the quality of items.
- It provides the products with extended shelf life and high market reach. Products can be transported to distant places with maintained quality.
- This process retains processed and cooked food’s nutritional properties, aroma, and flavor.
- Many food products, such as fruits, vegetables, meat, and bakery items, are sustainable under vacuum cooling.
(ii.) Disadvantages
- Due to the complexity of the equipment, this cooling process requires a high initial cost to install pumps and vacuum chambers and a high maintenance cost.
- Equipment installed in the vacuum cooling setup requires more energy consumption, which can lead to high costs.
- It is not suitable for all types of products because each food item has a different level of sensitivity, such as texture changes, moisture loss, and quality changes. These sensitivity levels need different treatment parameters.
- Staff should be trained to operate the process and equipment accurately. Due to technical complexity, sensors and control systems must be monitored to regulate the process.
- The vacuum cooling process involves water evaporation from the food product, which can cause moisture loss and changes in weight and texture.
- Its equipment requires enough space for installation in the facility.
1.6 Factors Affecting the Vacuum Cooling Process
Many factors significantly affect the effectiveness of the vacuum cooling process in the food industry are listed below:
(i.) Food Product:
It depends on the type of food product for efficient process implementation. Each food has a different surface area to volume ratio, moisture content, and texture properties that affect the process.
(ii.) Temperature:
Vacuum cooling involves the evaporation and cooling of the food product, so the initial temperature affects the cooling process. If the product has a high temperature, more energy will be required to cool it.
(iii.) Pressure:
If the vacuum pressure is reduced, the boiling point decreases, and the cooling effect is easily enhanced. Pressure should be maintained for an effective cooling process.
(iv.) Time:
The product is placed in a vacuum for an optimal time for effective treatment.
(v.) Loading in the chamber:
The chamber’s loading also affects the effectiveness of human calling. Overloading the product in the chamber can result in non-uniform cooling. The product should be placed in the chamber according to its capacity.
Environmental conditions Ecological conditions, such as humidity and temperature, influence the vacuum cooling process.
(vi.) Packaging:
Packaging for vacuum cold products should be permeable, allowing for moisture exchange. All operational parameters, such as vacuum rate and temperature or pressure, should be maintained for effective results and to prevent product damage.
(vii.) Pre-handling and post-handling:
Preliminary cooling techniques reduce the load in the chamber. After cooling, the product should be stored optimally using rehydration techniques.
2. Ultrasonic Assistant for Food Freezing
2.1 Introduction
It is a developed process that improves the food refrigeration process in hands and the quality of frozen food products. It uses high-frequency sound waves above 20kHz above the audible range for humans. These waves produce tiny bubbles in food liquid, and it is called cavitation. The bubbles produced have released energy and collapsed due to changes in pressure and temperature. Cavitation produces the energy that promotes the nucleation process. The equation process formulates the ice crystals. More heat transfer leads to effective food freezing. This process results in high-quality food products, efficient with reduced freeze burns.
2.2 Power Ultrasound Generation and Equipment
Power ultrasound generation includes several factors and steps to help food refrigeration:
Ultrasound transducers include Piezoelectric transducers that convert electrical energy into mechanical vibration and magnetostrictive transducers that produce ultrasound waves by magnetic field in specialized equipment.
Frequency/Power
Power ultrasound works on a system with sound waves between 20kHz and 100kHz. Low-frequency sound waves generally produce more potent cavitation effects. The power of ultrasound generation varies from a few watts to hundreds.
2.3 Equipment for Ultrasound Generation
Ultrasonic Transducer:
It converts electrical energy to mechanical waves. Materials used in the equipment are lead zirconate titanate and quartz, which change shape with the electrical power. The transducers are dipped in the liquid medium or can be mounted on a chamber.
Ultrasonic generator
It includes the electrical energy with the optimal power and frequency. Optimal frequency provides optimized cavitation.
Sonotrode
It provides ultrasonic waves directly to food by the transducer and is comprised of aluminum or titanium.
Cooling system
Freezing equipment is installed for emerging freezing and blast freezing. The freezing process uses ultrasonic waves to maximize the benefits.
2.4 Acoustic effect on the food freezing process
Acoustic waves have significant effects on food refrigeration mechanisms. Have a look at its effects:
Nucleation
Optimized ultrasonic waves result in optimized cavitation, leading to many nucleation sites for ice crystal formation. Small crystal formation provides uniformity and preserves food texture and quality.
Reduce the size of crystals.
Ultrasonic assistants help provide small ice crystals because they cause less damage to a food’s cell wall and help maintain its nutritional properties and texture.
Freezing rate:
Ultrasound waves increase the freezing process rate. These waves cause agitation, transferring heat from food to the freezing medium.
Uniform freezing
Ultrasonic waves should be maintained in the food product and freezing medium for uniform freezing, suitable for high-quality products.
Quality and texture
Ultrasound assistance in food freezing helps to maintain the texture and quality of food with retained nutrients.
Less freeze burns
Ultrasound waves do not cause freeze burns on food that may be due to oxidation or dehydration.
Efficiency in result:
The freezing process can be energy efficient because of the rapid rate of freezing time and heat transfer. Rapid freezing in less time will be cost-effective for the industry.
2.5 Major Functions of Power Ultrasound in Assisting Food Freezing
- Heat transfer aids in optimized cavitation by breaking the upper layer of food for efficient heat transfer.
- Ultrasound generates the cavitation for ice crystal formation. It includes energy release for more ice crystals.
- Ultrasound waves help to achieve uniform food processing by uniformly distributing energy. This results in reduced freeze burns.
- Power ultrasound waves decrease the energy needed to freeze and improve the process.
- Frozen food with tiny ice crystals melts and thaws quickly.
2.6 Factors Affecting the Power ultrasound efficiency
- Factors that affect the power ultrasound deficiency are ultrasound frequency and the size of cavitation bubbles.
- Lower frequency 20kHz to produce large cavitation bubbles
- High-frequency 40khz to create tiny cavitation bubbles
- Power intensity is high. The ultrasound power intensities in the hands are the gravitation process and nucleation or heat transfer. Excessive intensity results in damage to the food and causes excessive heating.
- A short exposure time will not produce the required product. An optimal time is adequate for the quality of the process.
- Food properties: each food has a different nutritional content and contains different moisture levels.
- Food with a high water content is subjected to ultrasound-assisted freezing more frequently to promote ice crystal formation. Food composition, such as fat, carbohydrates, and protein, affects the parameters of the ultrasound waves propagating through the food.
- Fluctuations in pressure and temperature also affect the power of ultrasound. The type of medium for ultrasound waves around the food also affects its efficiency.
2.7 Embodiment of Application
Embodiment of ultrasonic-assisted freezing applications in the food refrigeration industry includes the following key points:
- Designed ultrasonic freezing chambers
- ultrasonic probe system conveyor belt freezers with ultrasonic integration
- Immersion freezer with ultrasonic assistance
- ultrasonic assisted plate freezers
- batch freezers with ultrasonic transducers
3. High-Pressure Freezing
3.1 Introduction
High-pressure freezing is the rapid food refrigeration technique of treating food with ultrahigh pressure at low temperatures. For one year, many high-pressure processing models have been developed.
3.2 High-Pressure Freezing
High-pressure freezing is a technique that requires a high pressure of about 2100 bar and a low temperature of -196°C with less time for freezing the product. It is done by freezing the sample with liquid nitrogen, and the pressure is released after half a second. This ultra-quick freezing process immobilizes cell structure and components and preserves the sample.
3.3 Modelling of High-Pressure Freezing Process
You should have complete knowledge of the equipment’s design, the process’s physical principles, and the parameters for modelling high-pressure freezing. Physical principles include the phase changes of medium water under pressure.
The first law of thermodynamics applies to the high-pressure freezing process of food. During the compression and cooling phase, enthalpy calculation changes.
Process design and equipment involve selecting strong, noncorrosive materials to withstand high pressure. Vessel capacity is specified for pressure up to 200-600 MPa. Pumps and intensifiers are installed in the process for the desired pressure. Heat exchangers are set for the cooling system. Cryogenic fluids are used to cool the product quickly.
Mathematical equations involve
- Heat transfer equation
- Pressure distribution
- Phase change kinetics
Initial parameter conditions are set in the chamber and vessel. Software such as COMSOL, ANSYS, and Abaqus are used for FEM analysis. Always calibrate model data for accurate results. Perform sensitive analysis to analyze the parameter sensitivity.
4. Controlling the Freezing Process with Antifreeze Protein
4.1 Introduction
Antifreeze proteins are added to control the freezing process, ice crystal growth, and large ice crystals. This helps preserve texture and improve quality, thus contributes to food refrigeration.
4.2 Antifreeze Proteins
The mechanism of antifreeze proteins is ice-binding power. They absorb the ice crystal surface to prevent growth and recrystallization. Antifreeze proteins reduce the freezing point of water without affecting its boiling point and help form small-sized ice crystals.
Various AFPs exist, including fish AFPs, insect AFPs, plant AFPSs, and microbial AFPs. These antifreeze proteins can be directly added to food before freezing and are suitable for liquids such as dairy products, beverages, and sauces. If food is solid, then AFPs are coated on the food’s surface to prevent ice crystal growth.
The optimal concentration of AFPs should be added to prevent damage to food’s sensory characteristics. Monitor temperature changes and storage conditions to maintain effective results.
5. Conclusion
These are used in food with a smooth texture, like ice cream and frozen yogurt. AFPs are also used in fruits, vegetables, seafood, meat, and bakery products to maintain their texture and quality.
Innovation in food refrigeration involves vacuum cooling, ultrasonic assistance and high pressure freezing. Industries choose compatible process for desired results and fulfil the consumer demands. Learn more.