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High pressure homogenisation for microbial inactivation of liquid food


Key words dynamic pressure, high pressure, homogenisation, pasteurisation, emulsion, non-thermal, liquid, juice, milk
Latest version 2011/08/02
Completed by KU Leuven LFT

How does it work?

Primary objective Pasteurization of liquid foods, although the technology was originally developed for stabilization of emulsions.
Working principle High pressure homogenisation (HPH) is a purely mechanical process, which is evoked by forcing a fluidic product through a narrow gap (the homogenizing nozzle) at high pressure (150-200 MPa, or 350-400 MPa for ultra high pressure homogenization, UHPH) (1,2). The reduction or destruction of microorganisms by HPH is probably due to several physical phenomena, such as quick pressure drop, cavitation, shearing, turbulence and collision and the coinciding temperature increase. These physical phenomena could increase the permeability or rupture of the cell membrane, causing cell death (1).

For a single pass treatment to result in adequate kill, relatively high pressures are needed (e.g. 300 MPa). However, the liquid food can also be subjected several times to the treatment (multiple passes) at lower pressures (e.g. 150 MPa), although with reduced cumulative efficiency in each additional pass. Complete inactivation might be difficult to attain, as for many strains, survival of a fraction resistant to high pressure homogenization has been shown. Nevertheless, significant increase in shelf-life compared to untreated fruit juice (for instance) can be obtained, both at the microbiological and the quality level (4). Combined with other mild physical or chemical stresses (such as mild heat treatment, hydrogen peroxide and low pH), high pressure homogenization can also induce significant spore inactivation, for instance in Bacillus cereus and Bacillus subtilis spores (5).

Additional effects The technology was originally developed for stabilization of emulsions, although these are prepared at lower pressures.

For preservation purposes, also enzymes negatively affecting the food quality need to be inactivated. High pressure homogenization has been shown to (partly) inactivate pectin methylesterase in orange juice (6), milk plasmin (7) and pectate lyase in banana juice (8). Heating (17-21°C per 100 MPa) occurs during high pressure homogenisation because of adiabatic heating, high turbulence, shear and cavitation forces (dissipation of pressure energy as heat) (2). To minimize the heat damage, after the homogenization valve, a cooling heat exchanger needs to be foreseen (9).To differentiate between high pressure homogenized milk and heat treated milk, thermal indicators of beta-lactoglobulin denaturation and non-enzymatic browning (absorbance at 340 nm) can be used.

Important process parameters pressure, number of cycles, inlet temperature (10,11,12), pressure release valve design (although gap width and scale supposedly do not affect the efficacity (10,12)), valve seat materials.
Important product parameters The effectivity of the process depends on the type of microorganism. Gram negative bacteria tend to be more sensitive to high pressure homogenisation (probably because of their thinner cell wall), milk fat content, food particle size, pH

What can it be used for?

Products liquid foods (apple juice (10), citrus juice (4), milk (9), ...)
Operations pasteurisation, emulsification, homogenization
Solutions for short comings pasteurisation technology not based on heat alone

What can it NOT be used for?

Products solid foods or liquid foods with large particles
Operations Sterilisation by high pressure homogenization might be limited
Other limitations Many microbial strains show high pressure homogenization resistant fractions. These need to be below the acceptable level for shelf life (4).

The limited shelf-life obtained indicates that HPH of raw milk (at 70°C and 250 MPa), is not a suitable single-step alternative to pasteurisation for extending the shelf-life of milk (11). This can be however due to the knock-out of the endogenous antimicrobial effect of lactoperoxidase that is not entirely inactivated at lower temperatures (30°C and 300 MPa) during high pressure homogenisation, thus contributing to a longer shelf-life of HPH treated milk (11). HPH is not able to inactivate heat resistant enzymes produced by psychotropic microorganisms, requiring a good initial quality of milk to obtain stable milk during its storage (9). Energy efficiency of HPH needs to be improved. In UHPH, depending on the dispersion and emulsion formulation, 41-63% of the energy is lost as heat (2).

Risks or hazards
  • Spore survival
  • Heating of heat-sensitive products can occur at high pressures, without when adequate temperatureis not controlcontrolled adequately.


Maturity High pressure homogenization is a mature technology in milk homogenization. The pasteurization effect is not yet applied in food industry.
Modularity /Implementation High pressure homogenization is a continuous process that can replace an existing pasteurization step (9). However, preceeding and following heat exchangers (heating to e.g. 30°C before treatment and cooling after treatment, respectively) need to be foreseen.
Consumer aspects No issues expected
Legal aspects As high pressure homogenization has been used already for a long time in the dairy industry, albeit at lower pressure levels, no issues with regard to the Novel Food Regulation are expected
Environmental aspects The energy cost can be reduced by working at lower pressures for multiple passes, although with reduced cumulative inactivation efficiency in each additional pass..

Further Information

Institutes KU Leuven LFM, CERPTA, University of Salerno
Companies Stansted Fluid Power, GEA Niro Soavi, FBF Italia
References 1. Stang M., Schuchmann, H., Schubert, H. (2001). Emulsification in High-Pressure Homogenizers. Engineering in Life Sciences 1(4), 151-157.

2. Dumay, E., Chevalier-Lucia, D., Picart-Palmade, L., Benzaria, A., Gràcia-Julià, A., Blayo, C. (2012) Technological aspects and potential applications of (ultra) high-pressure homogenisation. Trends in Food Science and Technology. In press.

3. Diels, A.M.J. & Michiels C.W. (2006) High-pressure homogenization as a non-thermal technique for inactivation of microorganisms. Critical Reviews in Microbiology, 32, 201-216.

4. Maresca, P., Donsì F., Ferrari, G. (2011) Application of a multi-pass high-pressure homogineization treatment for the pasteurisation of fruit juices. Journal of Food Engineering, 104, 364-372.

5. Chaves-López, C., Lanciotti, R., Serio, A., Paparella, A., Guerzoni, E., Suzzi, G. (2009) Effect of high pressure homogenization applied individually or in combination with other mild physical or chemical stresses on Bacillus cereus and Bacillus subtilis spore viability. Food Control 20, 691–695

6. Welti-Chanes, J., Ochoa-Velasco, C.E. & Guerrero-Beltran, J.A. (2009) High-pressure homogenization of orange juice to inactivate pectinmethylesterase. Innovative Food Science and Emerging Technologies, 10, 457–462.

7. Pereda, J., Ferragut, V., Buffa, Guamis, B., Trujillo, A.J. (2008). Proteolysis of ultra-high pressure homogenised treated milk during refrigerated storage. Food Chemisty, 111, 696–702.

8. Calligaris, S., Foschia, M., Bartolomeoli, I., Maifreni, M., Manzocco, L. (2012) Study on the applicability of high-pressure
homogenization for the production of banana juices. LWT - Food Science and Technology 45, 117-121.

9. Pereda, J., Ferragut, V., Quevdo, J.M., Guamis, B., Trujillo, A.J. (2007) Effects of ultra-high pressure homogenization on microbial and physicochemical shelf life of milk. Journal of Dairy Science, 90, 1081-1093.

10. Donsì F., Ferrari, G. , Lenza, E., Maresca, P. (2009) Main factors regulating microbial inactivation by high-pressure homogenization: Operating parameters and scale of operation. Chemical Engineering Science, 64, 520-532.

11. Pedras, M.M., Pinho, C.R.G., Tribst, A.A.L., Franchi, M.A., Cristianini, M. (2012) The effect of high pressure homogenization on microorganisms in milk. International Food Research Journal 19(1): 1-5.

12. Cavender, G.A. & Kerr, W.L. (2011) Inactivation of vegetative cells by continuous high-pressure processing: new insights on the contribution of thermal effects and release device. Journal of Food Science 76, E525-E529.

13. Smiddy, M.A., Martin, J.-E., Huppertz, T., Kelly, A.L. (2007) Microbial shelf-life of high-pressure-homogenised milk. International Dairy Journal 17, 29–32

14. Cortés-Muñoz, M., Chevalier-Lucia,D., Dumay, E. (2009). Characteristics of submicron emulsions prepared by ultra-high pressure homogenisation: Effect of chilled or frozen storage. Food Hydrocolloids 23, 640–654.

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Created by LiesbethV on 3 August 2011, at 10:40