Fundamental Food Microbiology, Third Edition - Fuad Fathir

CONTROL BY NOVEL PROCESSING TECHNOLOGIES 523
C. Destruction of Microbial Cells 3,6–10
1. Bacterial Cells
There have been many studies on the pressure-induced viability loss and sublethal
injury of foodborne bacterial cells, with more studies being reported for the pathogens.
Some of these include pathogens such as Salmonella serovars, Lis. monocytogenes,
Staphylococcus aureus, Yersinia enterocolitica, Vibrio parahaemolyticus,
and Esc. coli O157:H7, and spoilage bacteria such as Pseudomonas spp., Serratia
liquefaciens, Leuconostoc mesenteroides, and Lactobacillus sake. The antibacterial
effect of hydrostatic pressure can be summarized as follows:
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• Gram-negative bacteria are relatively more susceptible than Gram-positive bacteria
and rods are more sensitive than cocci.
• Species and strains of a species differ in sensitivity.
• A strain can be sensitive to thermal treatment but resistant to pressure treatment
and vice versa.
• Pressure resistance increases with higher consistency, lower A w, higher pH, and
higher lipid content of the suspending media.
• Viability loss increases directly with the increase in pressure, temperature, and
time, with time having the least effect.
• Pressurization also induces sublethal injury in viable cells.
• Suitable antimicrobial agents (physical and chemical) can be included during
pressurization to enhance viability loss.
Bacterial cell death in a given set of pressurization parameters occurs in a predictable
way. Like in thermal treatment, the death rate follows first-order kinetics, especially
at a pressure above 300 MPa and a pressurization temperature of 45�C and above.
D values of eight different foodborne bacterial cell suspensions in peptone solution
following pressurization at 345 MPa and 50�C were found to