Improved Energy Efficiency of High-Pressure Processing
High-Pressure Processing (HPP) is a non-thermal food preservation method that ensures microbial safety and extends shelf life while maintaining food quality, though its energy inefficiencies due to entrapped air and gas present operational challenges for sustainable implementation. Ultrasonic degassing the pressure-transmitting liquid and liquid foods reduces compressibility, minimizing energy losses and improving the overall efficiency of the HPP process.
High-Pressure Processing (HPP): Energy Efficiency Challenges
High-Pressure Processing (HPP) is one of the leading non-thermal food preservation techniques, offering a combination of microbial inactivation and quality retention for liquid and solid food products. The HPP technology achieves food safety and extended shelf life without compromising the sensory or nutritional properties of food, aligning with the growing consumer preference for minimally processed products. However, the energy demands of HPP pose significant operational challenges, particularly due to inefficiencies introduced by entrapped air and gas within the process. Addressing these challenges is key to unlocking its full potential for sustainable food production.
Overview: HPP and its Energy Challenges
| HPP Definition | Challenges | Solution |
|---|---|---|
| A non-thermal food preservation method that ensures microbial safety and extends shelf life while maintaining food quality. | Energy inefficiencies due to entrapped air and gas, increasing operational costs. | Ultrasonic degassing reduces compressibility, minimizing energy losses and improving HPP efficiency. |
The Solution: Ultrasonic Degassing of HPP Liquids
Ultrasonic degassing offers an efficient solution to enhance the energy efficiency of High-Pressure Processing (HPP) by removing entrapped air and gas from both the pressure-transmitting liquid and liquid food products. By applying power ultrasound, ultrasonic cavitation promotes the rapid coalescence and release of gas bubbles, reducing compressibility and minimizing energy losses during compression. This optimization not only lowers operational costs but also enhances process stability, making HPP more sustainable and effective for food preservation.
Ultrasonic Degassing of Water
How HPP Works
High-Pressure Processing (HPP) works by subjecting food products, typically in flexible and waterproof packaging, to extremely high pressures of up to 6,000 bar (600 MPa). The process occurs in a water-filled high-pressure vessel and a straightforward sequence:
- Loading: Packaged products are placed into plastic baskets and conveyed into the high-pressure vessel.
- Pressurization: Water is filled into the vessel, acting as the pressure-transmitting medium. The system is then pressurized to the desired level, typically maintained for a few minutes.
- Isostatic Effect: Pressure is applied uniformly and instantaneously across the product, regardless of its size, shape, or composition. This isostatic pressure inactivates food-borne microorganisms and spoilage enzymes without crushing or deforming the product.
- Depressurization and Unloading: The vessel is depressurized, water is drained, and the treated products are conveyed out, ready for consumption or further processing.
High Pressure Processing (HPP)
© Balakrishna et al., 2020
The HPP method ensures food safety while preserving taste, texture, and nutrient content. However, this process requires significant energy input, a factor influenced by several operational inefficiencies.
Challenges of High Energy Consumption in HPP
One of the primary drawbacks of HPP is its high energy consumption. The energy-intensive nature of the process arises from:
- Pressurization of Water (Coupling Liquid): The water used to transmit isostatic pressure requires significant energy to compress and maintain the target pressure.
- Entrapped Air and Gas in the Coupling Liquid: Air bubbles within the water reduce pressure transmission efficiency, increasing energy requirements. These bubbles compress during pressurization, absorbing energy that could otherwise be used to treat the food product.
- Gas in Packaged Products: Air or gas trapped within packaged foods (e.g., in canned or semisolid products) similarly contributes to energy loss. The compression of internal gas pockets requires additional energy and can interfere with pressure uniformity.
- Thermal Energy Losses: While HPP is considered a non-thermal process, some energy dissipates as heat due to water compression and equipment friction. This increases operational costs and cooling requirements.
Ultrasonic flow cell for degasification of liquids and pasteurization of food.
Impacts of Entrapped Air and Gas on HPP Energy Demand
The presence of air and gas significantly impacts the efficiency of HPP:
- Reduced Pressure Transmission Efficiency: Air and gas compress more easily than liquids, meaning additional energy is required to achieve the same pressure within the vessel.
- Longer Processing Times: Entrapped air and gas delay the stabilization of isostatic pressure, extending cycle durations.
- Energy Waste: Compressed gas pockets release energy upon depressurization, which cannot be recovered, contributing to overall inefficiency.
These effects are especially pronounced when processing food products with naturally high air content or packaging that traps headspace gas, such as canned or vacuum-packed items.
Strategies to Address Energy Challenges in HPP
Efforts to improve the energy efficiency of HPP focus on reducing the influence of air and gas within the system:
Pre-Treatment – Ultrasonic Degassing:
The application of ultrasound to remove dissolved air and gas from the coupling liquid and food products can significantly reduce energy waste. Ultrasonic cavitation effectively disrupts gas bubbles, allowing them to escape before pressurization.
Additionally, products can set after ultrasonic degasification under vacuum, particularly canned or sealed items.
Decrease of dissolved oxygen with time using the sonicator UP400ST at amplitudes of 100 %, 80 %, 60 %, 40% and 20 %.
Study: ©Rognerud et al., 2020.
Sonication as Alternative for Sustainable HPP
Hybrid HPP systems combining high-performance ultrasound with mild heat (thermosonication) or with elevated pressure and mild heat (manothermosonication) are promising alternative techniques that provide reliable homogenization and pasteurization under mild conditions and at low energy consumption. Since ultrasonic pasteurization is an inline process, even large volumes can be processed with high cost-efficiency.
Learn more about Hielscher sonicators for inline pasteurization of liquid foods!
Whilst HPP is widely used for food processing, its energy-intensive nature, compounded by inefficiencies from entrapped air and gas, poses a critical challenge. By integrating strategies such as ultrasonic degassing, the food industry can enhance the sustainability and cost-effectiveness of HPP.
Hielscher Ultrasonics is the trusted partner for process solutions in HPP optimization, offering advanced ultrasonic technology to improve energy efficiency and process reliability. Additionally, Hielscher provides innovative solutions for synergistic ultrasound-assisted food pasteurization, ensuring high-quality and safe food products.
Literature / References
- Rognerud, Maren; Solemslie, Bjørn; Islam, Md Hujjatul; Pollet, Bruno (2020): How to Avoid Total Dissolved Gas Supersaturation in Water from Hydropower Plants by Employing Ultrasound. Journal of Physics: Conference Series 2020.
- Oner M.E. (2020): The effect of high pressure processing or thermosonication in combination with nisin on microbial inactivation and quality of green juice. Journal of Food Processing and Preservation 2020; 44:e14830.
- Evelyn, Filipa V.M. Silva (2016): High pressure processing pretreatment enhanced the thermosonication inactivation of Alicyclobacillus acidoterrestris spores in orange juice. Food Control, Volume 62, 2016. 365-372.
- Balakrishna, Akash Kaushal, Md Abdul Wazed, Mohammed Farid (2020): A Review on the Effect of High Pressure Processing (HPP) on Gelatinization and Infusion of Nutrients. Molecules 25 (10), 2020. 2369.
Frequently Asked Questions
What is Degassing of Pressure Transmitting Liquids?
Degassing is the removal of dissolved and entrapped gases from the liquid used in High-Pressure Processing (HPP) to improve energy efficiency and process stability. By eliminating compressible gases, degassing reduces pressure loss, enhances uniform pressure distribution, and minimizes cavitation-related wear in HPP systems.
What is High Pressure Processing HPP Treatment?
HPP is a non-thermal food preservation method that applies hydrostatic pressures of up to 600 MPa to inactivate microorganisms while preserving sensory and nutritional qualities. It extends shelf life, ensures food safety, and retains bioactive compounds without using heat, making it suitable for fresh and minimally processed foods.
What is the Problem with using High Pressure Processing HPP?
The primary challenges of HPP include high energy consumption, process inefficiencies due to entrapped air in pressure-transmitting liquids, and high equipment costs. Additionally, while effective against most vegetative pathogens, HPP does not inactivate bacterial spores without additional hurdles such as mild heating (pressure-assisted thermal processing, PATP).
What is the Difference between Pasteurization and HPP?
Pasteurization is a thermal process that inactivates microorganisms through heat (typically 60–85°C), potentially altering food texture and nutritional composition. HPP, in contrast, is a non-thermal method that achieves microbial inactivation through pressure, preserving the food’s original taste, texture, and nutrients while extending shelf life.
Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers from lab to industrial size.