Fundamental Food Microbiology, Third Edition - Fuad Fathir

CONTROL BY A COMBINATION OF METHODS (HURDLE CONCEPT) 533
G. Hydrostatic Pressure Processing (HPP)
The antibacterial effect of ultrahigh hydrostatic pressure can be increased by incorporating
mild heat, slightly low pH, bacteriocins, lysozyme, and chitosan. Spores
are difficult to destroy unless very high pressure is used (@700MPa). However, after
low-pressure treatment (�100MPa), the spores may be induced to germinate, which
can then be killed by higher pressure, mild heat, bacteriocins, or other antibacterial
agents (see Chapter 39).
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IV. CONCLUSION
Many of the control methods listed, such as low heat, low pH, low A w, low temperature,
and hydrostatic pressure, induce sublethal stress among the surviving cells
and spores. Cells and spores injured by one parameter become sensitive to other
parameters and are killed in their presence. Sublethal injury to microbial cells and
spores and increased susceptibility of injured cells and spores to one or more
preservation methods can play important roles in controlling microorganisms by a
combination of factors. 5
It will be important to study the beneficial effect of combining different parameters
at different levels to determine their antimicrobial efficiency against target
microorganisms in food systems. The hurdle concept is based on the scientific
concept that when two or more methods are used together the combinations are
more effective, even at a much lower treatment level. However, because of the large
number of possibilities, actual product challenge studies may not be possible for all.
Instead, at the initial stage, computer simulation by using multifactorial parameters
can be designed that take into consideration the characteristics of a food. Then
limited number of selected parameters can be studied by product inoculation. These
methods are now being developed (see Appendix B).
REFERENCES
1. Leistner, L. and Rodel, W., The stability of intermediate moisture foods with respect
to microorganisms, in Intermediate Moisture Food, Applied Science Publishers,
Englewood, NJ, 1976, p. 120.
2. Mossel, D.A.A., Essentials and perspectives of the microbial ecology of foods, in
Food Microbiology: Advances and Prospects, Academic Press, London, 1983, p. 1.
3. Scott, V.N., Interaction of factors to control microbial spoilage of refrigerated food,
J. Food Prot., 52, 431, 1989.
4. Gould, G.W. and Jones, M.V., Combination and synergistic effects, in Mechanisms
of Action of Food Preservation Procedures, Gould, G.W., Ed., Elsevier Applied
Science, New York, 1989, p. 401.
5. Ray, B., Sublethal injury, bacteriocins and food microbiology, ASM News 59, 285,
1993.