A new non-thermal food processing method called Dense Phase Carbon Dioxide (DPCD) makes use of the molecular effects of CO2 at pressures lower than 50 MPa to inactivate microorganisms and enzymes, without subjecting the product to adverse heat effects and maintaining its quality, similar to fresh produce. (Liao et al., 2009) This technique, also known as the cold pasteurization technique gained significance in food pasteurization after Fraser identified its antimicrobial properties on microorganisms in 1951.
In the DPCD process, food comes into contact with pressurized sub- or supercritical CO2 for a specific duration. The CO2 pressure typically ranges from 7.0 to 40.0 MPa, while the process temperature generally falls between 20 to 60°C. The treatment duration varies depending on the process type, with continuous processes lasting around 5 to 10 minutes and semi-continuous or batch processes lasting from 120 to 140 minutes. Furthermore, CO2 is recognized as a material that is generally recognized as safe (GRAS), which makes it appropriate for food processing due to its inert, affordable, non-toxic and non-flammable characteristics, as stated by Ferrentino and Spilimbergo in 2017.
The carbon dioxide exists in different states of matter with its own peculiar characteristics (Fig. 1). A Dense phase is the phase of matter that remains fluid and denser than the gaseous phase and this includes the liquid and supercritical regions of a phase diagram. Due to the higher density, the physical properties of CO2 get altered and becomes a more effective solvent. The penetration of supercritical CO2 through a microbial cell membrane attributes a decrease in viscosity and an increase in diffusivity properties. (Chen et al. 2009)
The microbial inactivation mechanism by DPCD is illustrated in Fig. 2. It involves a number of processes, including acidification of the solution, the inhibition of CO2 and bicarbonate ions by molecules, modification of the cell membrane, the removal of cellular components and disturbance of intracellular electrolyte balance. The excessive entry of CO2 into cells leads to a decrease in internal pH, which disrupts crucial metabolic processes, including enzymes, resulting in the deactivation of microorganisms, (Gunes et al., 2005). The removal of lipids and other essential substances from cells or membranes also contributes to their deactivation.
Cells subjected to DPCD treatment (pressure 7 MPa, temperature 30°C and time as 10 min.) undergo irreparable cellular destruction, loss of salt tolerance, UV-absorbing material leakage, intracellular ion release and reduced proton permeability, (Mohapatra, 2017). The cellular biological system may also suffer fatal harm from the build-up of CO2 pressure within the cytoplasm of bacterial cells. (Liao et al., 2009)
Factors affecting Microbial Inactivation by DPCD
Application of DPCD Technique in Foods
Dense Phase Carbon Dioxide (DPCD) has found several applications in the food industry, owing to its unique properties and ability to provide non-thermal processing. Some of the common applications of DPCD in foods are microbial and enzyme inactivation, extraction of bioactive compounds, texture modifications, preservation of nutritional quality, decontamination of food contact surfaces, etc. For apple syrup, DPCD treatment completely eliminated mesophilic microorganisms, total coliforms, yeasts, moulds and polyphenol oxidase activity, with minimal impact on pH, colour and total acidity. (Ferrentino and Spilimbergo 2017)
Grape juice treated with DPCD showed a significant reduction in yeast population, with higher CO2 concentrations, temperature and pressure enhancing the inactivation rate, (Gunes et al. (2005). DPCD exhibited a complete inactivation of polyphenol oxidase and peroxidase, increased vitamin C and total phenol content and minor effects on pH and colour in commodities, such as Pao cai (Xing et al., 2023), mango syrup (Tang et al. (2021). DPCD treatment of red grapefruit juice prevented microbial growth and increased cloud values, (Ferrentino et al., 2009). Pickled carrots treated with DPCD showed improved firmness, appearance, β-carotene content and overall pectin content, (Wang et al., 2019). DPCD treatment of Hami melon had minimal effects on aroma and flavour, but led to a decrease in vitamin C concentration. (Chen et al., 2010)
Advantages and Disadvantages of the DPCD Process
1. Chen, J., Zhang, J., Feng, Z., Song, L., Wu, J. and Hu, X., 2009. Influence of thermal and dense-phase carbon dioxide pasteurization on physicochemical properties and flavor compounds in Hami melon juice. Journal of Agricultural and Food Chemistry, 57(13), pp.5805-5808.
2. Ferrentino, G. and Spilimbergo, S., 2017. Non-thermal pasteurization of apples in syrup with dense phase carbon dioxide. Journal of Food Engineering, 207, pp.18-23.
3. Ferrentino, G., Plaza, M.L., Ramirez-Rodrigues, M., Ferrari, G., Balaban, M.O., 2009. Effects of dense phase carbon dioxide pasteurization on the physical and quality attributes of a red grapefruit juice. J. Food Sci. 74, E333eE341.
4. Gunes, G., Blum, L.K. and Hotchkiss, J.H., 2005. Inactivation of yeasts in grape juice using a continuous dense phase carbon dioxide processing system. Journal of the Science of Food and Agriculture, 85(14), pp.2362-2368.
5. Liao, X., Zhang, Y., Bei, J., Hu, X. and Wu, J., 2009. Alterations of molecular properties of lipoxygenase induced by dense phase carbon dioxide. Innovative Food Science & Emerging Technologies, 10(1), pp.47-53.
6. Mohapatra, A. (2017). Dense Phase Carbon Dioxide: A Novel Non-Thermal Technique for Inactivation of Micro-Organisms in Food.
7. Sibel and Murat, 2006. Review of dense phase CO2 technology: microbial and enzyme inactivation, and effects on food quality. Journal of food science. 71 (1), pp. R1-R11
8. Tang, Y., Jiang, Y., Jing, P. and Jiao, S., 2021. Dense phase carbon dioxide treatment of mango in syrup: Microbial and enzyme inactivation, and associated quality change. Innovative Food Science & Emerging Technologies, 70, p.102688.Patchigolla, K., Oakey, J.E. and Anthony, E.J., 2014. Understanding dense phase CO2 corrosion problems. Energy Procedia, 63, pp.2493-2499.
9. Wang, D., Ma, Y., Sun, X., Zhang, M., Zhao, Y. and Zhao, X., 2019. Effect of dense phase carbon dioxide treatment on physicochemical and textural properties of pickled carrot. CyTA-Journal of Food, 17(1), pp.988-996.
10. Xing, Y., Yi, R., Yue, T., Bi, X., Wu, L., Pan, H., Liu, X. and Che, Z., 2023. Effect of dense phase carbon dioxide treatment on the flavor, texture, and quality changes in new-paocai. Food Research International, p.112431.
About the Authors:
1. Shilpa S. Selvan
ICAR – Central Institute of Post-Harvest Engineering & Technology,
Abohar, Punjab, India.
Email ID: firstname.lastname@example.org
2. Naveen Jose
ICAR – National Institute of Natural Fibre Engineering & Technology,
3. Aseeya Wahid
ICAR – Central Institute of Agricultural Engineering,
4. Abhishek Patel
ICAR – Central Institute of Agricultural Engineering,
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