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High-Pressure Carbon Dioxide (HPCD) in Food Processing

By PMG Engineering ·

Thermal treatment of food products significantly impacts their nutritional and organoleptic values. In many cases, it is undesirable, especially for thermally sensitive food products. The most common practice in the dairy industry is High-Temperature Short-Time (HTST) pasteurization, where liquid milk is heated between 70-78°C. While this reduces microbial load, it can also cause nutrient loss, enzyme degradation, and off-flavor development due to overheating.

An emerging non-thermal pasteurization technique called High-Pressure Carbon Dioxide (HPCD) is gaining attention as an alternative to conventional thermal pasteurization. HPCD has been proven to have bactericidal effects, making it a promising solution in the food industry.

What is High-Pressure Carbon Dioxide (HPCD)?

HPCD technology involves dissolving carbon dioxide (CO2) under high pressure into liquid food products to inactivate pathogenic microbes. This technique is particularly useful for thermally sensitive foods such as milk and dairy products, offering a viable alternative to conventional pasteurization.

Solubility of Carbon Dioxide in Dairy Products

The amount of CO2 dissolved in liquid is crucial for its efficiency in microbial inactivation. During the milking process, milk naturally contains approximately 5 millimoles of CO2, but this decreases over time as it equilibrates with atmospheric CO2.

Factors Affecting CO2 Solubility in Milk:

  • Temperature: Higher temperatures reduce CO2 solubility but increase diffusion rates.
  • Viscosity: Increased viscosity enhances gas diffusion in higher-temperature products.
  • CO2 Infusion: A moderate CO2 infusion can lower the freezing point of milk, but excessive levels may affect its quality.

How HPCD Inactivates Microorganisms

The antimicrobial effect of HPCD is primarily due to its acidification and solvent properties. The bactericidal effect is maximized when CO2 reaches a supercritical state, where it:

  1. Penetrates microbial cells and disrupts their structure.
  2. Lowers the pH, inhibiting microbial growth.
  3. Combines pressure and temperature effects to destroy pathogens effectively.

Effects of HPCD on Microbes:

  • Low pressure & low temperature: Inhibits microbial growth and alters pH.
  • High pressure & moderate temperature: Disrupts cell membranes, leading to microbial inactivation.

Key Processing Parameters Influencing HPCD Efficiency

Several factors determine the effectiveness of HPCD in food processing:

1. Temperature

  • Higher temperatures increase CO2 diffusion into microorganisms, enhancing its lethal effect.
  • The optimal range for HPCD treatment is 20-45°C.

2. Pressure

  • Increased pressure reduces the exposure time required to inactivate microorganisms.
  • Fast depressurization further enhances microbial destruction.

3. Agitation

  • Without agitation, only surface-level microbes are exposed to CO2.
  • With agitation, CO2 reaches all microbial cells, improving efficiency.

Impact of Product Composition on HPCD Effectiveness

Different food compositions influence the effectiveness of HPCD processing:

  • Starch: No negative impact on microbial inactivation.
  • Whey protein: Reduces the efficiency of CO2 processing.
  • Water content: Lower water content reduces CO2 efficiency, as it acts as a microbial barrier.
  • Salt concentration:
  • Low salt levels reduce CO2 potency.
  • High salt levels improve microbial inactivation.

Potential of HPCD in the Dairy Industry

For commercial application, HPCD pasteurization is best suited for low-viscosity dairy products such as skimmed milk. Thick dairy products are harder to treat using this method due to their high viscosity.

Attributes Beneficial for HPCD Processing:

  • Low fat content
  • High water activity
  • Low to moderate sugar content
  • Alcohol and protein presence
  • Low pH
  • Low viscosity

Conclusion: HPCD as a Future-Ready Food Processing Technology

HPCD balance food safety, nutritional integrity, and sustainable processing. Whether you're designing a new food factory, upgrading an existing plant, or exploring non-thermal food technologies, a food industry consultant can guide your transformation.

Frequently asked
How does HPCD kill bacteria without heat?
High-Pressure Carbon Dioxide works through acidification and solvent action rather than heat. The bactericidal effect peaks when CO2 reaches a supercritical state: it penetrates microbial cells and disrupts their structure, lowers pH to inhibit microbial growth, and combines pressure and temperature effects to destroy pathogens. At low pressure and low temperature it mainly inhibits growth and alters pH; at high pressure with moderate temperature it disrupts cell membranes, causing inactivation.
What temperature and pressure range should we design for in an HPCD system?
The optimal temperature range for HPCD treatment is 20-45°C. Higher temperatures increase CO2 diffusion into microorganisms and enhance the lethal effect. On the pressure side, increased pressure reduces the exposure time needed to inactivate microorganisms, and fast depressurization further enhances microbial destruction. These parameters are traded off against each other when sizing an HPCD process for a liquid food product.
Which dairy products are actually suitable for HPCD pasteurization?
For commercial application, HPCD pasteurization is best suited to low-viscosity dairy products such as skimmed milk. Thick, high-viscosity dairy products are much harder to treat by this method. Product attributes that favour HPCD processing include low fat content, high water activity, low to moderate sugar content, the presence of alcohol and protein, low pH and low viscosity.
Why would we consider HPCD instead of HTST pasteurization for milk?
HTST pasteurization heats liquid milk to 70-78°C, which reduces microbial load but can cause nutrient loss, enzyme degradation and off-flavour development from overheating. HPCD is a non-thermal alternative that dissolves CO2 under high pressure into liquid food to inactivate pathogenic microbes, with proven bactericidal effects. It is particularly attractive for thermally sensitive products such as milk and dairy, where thermal damage to nutritional and organoleptic quality is undesirable.
Does product composition affect how well HPCD works?
Yes. In HPCD processing, starch has no negative impact on microbial inactivation, while whey protein reduces CO2 processing efficiency. Lower water content reduces CO2 efficiency because water acts as a microbial barrier. Salt concentration matters too: low salt levels reduce CO2 potency, whereas high salt levels improve microbial inactivation. Composition should therefore be assessed product by product before committing to HPCD.
Is agitation necessary during HPCD treatment?
Agitation is important for HPCD efficiency. Without agitation, only surface-level microbes are exposed to the CO2, leaving cells in the bulk untreated. With agitation, CO2 reaches all microbial cells, improving inactivation efficiency across the product volume. Agitation should therefore be built into the design of any HPCD vessel or treatment stage for liquid food products.
CITE THIS

PMG Engineering. (2020). High-Pressure Carbon Dioxide (HPCD) in Food Processing. PMG Engineering. https://pmg.engineering/Article/60/high-pressure-carbon-dioxide-hpcd-in-food-processing/

https://pmg.engineering/Article/60/high-pressure-carbon-dioxide-hpcd-in-food-processing/