Food sterilisation under high pressure- Fundamentals,new insights and challenges
Special Symposium - Innovations in Food Technology (LMC Congress)
Hygiene, Hygienic Design & Unit Operations (Food-5a)
Keywords: sterilisation, high pressure, spore, Bacillus
The mechanism of inactivation of bacterial spores by heat and pressure is still a matter of discussion.Obviously, the change of the pH-value under pressure plays a major role in inactivation of microorganisms, but its behavior has rarely been investigated. Since acid/base equilibria shift under pressure, the pressure behaviour of water and buffer systems had to be investigated and presented in p-T-diagrams. Pressure stable buffer solutions like Tris and ACES as well as temperature stable systems e.g. Phosphate and Citrate were used. Due the compression of water up to 1000 MPa produces a strong temperature increase, temperature dependencies of all parameters need to be considered. After high pressure inactivation of bacterial spores at different temperatures and pH-values these calculations could be supported. Due to preparation, storage and handling of highly concentrated spore suspensions the clumping and the formation of aggregates can hardly be avoided. Consequently, the impact of the agglomeration size distribution on the quantitative assessment of B. stearothermophilus spore inactivation was determined by using a three-fold dynamic optical back-reflexion measurement. Two limiting cases have been discriminated in mathematical modelling: three dimensional, spherical packing for maximum spore count and two dimensional, circular packing for minimum spore count of a particular agglomerate. Thermal inactivation studies have been carried out in thin glass capillaries, where by using numerical simulations the non-isothermal conditions were modelled and taken into account. It is shown that the lag phase often found in thermal spore inactivation (shoulder formation) can sufficiently be described by first-order inactivation kinetics when the agglomeration size is considered. The physiological response of B. licheniformis spores to high pressure and thermal inactivation was investigated using multiparameter flow cytometry. Spores were treated by heat-only at 121°C, by high pressure at 150 MPa (37°C), or by a combined high pressure and heat treatment at 600 MPa and 77°C, and then dual stained with the fluorescent dyes SYTO 16 and propidium iodide. For pressure treated spores, but not heat-only treated spores, four distinct populations were detected by flow cytometry, and for these we suggest a three step model of inactivation involving a germination step following hydrolysis of the spore cortex, an unknown step, and finally an inactivation step with physical compromise of the spore’s inner membrane. An understanding of these effects and mechanisms will aid the safety assessment of pressure assisted thermal sterilisation, in turn facilitating the adoption by industry and commercialisation of such processes.
See the full pdf manuscript of the abstract.
Presented Thursday 20, 11:00 to 11:15, in session Hygiene, Hygienic Design & Unit Operations (Food-5a) Continued.
