With the traditional thermal food-processing technique, the key
role of high temperature is to ensure food safety and inhibit the
growth of pathogens. Thus, the pasteurization value at various
temperatures must be carefully evaluated. However, this has led to
a long-standing unsolvable challenge in food processing, which is
to achieve the lowest requirement for microorganism safety while
avoiding the damage to food quality by high temperatures. The
development of HPP can satisfy the above requirements. High
pressure can inhibit the growth of pathogens and maintain a level
of food quality and freshness similar to that of minimal processing.
Although HPP has been developed for over 100 years in American
and Japan, it remains an emerging technique in many countries. All
new processing techniques must conform to food safety standards
before commercial application. Additionally, because eating habits
vary in each country, the definition of food safety differs significantly.
Therefore, when applying HPP, many parameters conditions
such as pressure, temperature, time, and pH value must be
considered. These parameters need to be set to a range that can
effectively control microorganism safety risks before they can
conform to relevant regulations in Taiwan. Consequently, before
initiating HPP product development, the pressure-resistant characteristics
of pathogenic marker organisms, as well as their possible
physiological reactions after HPP, must be fully understood.
Because the pressure resistance of microorganisms is not uniform,
unsuitable pressure processing conditions are not only incapable of
inhibiting microbial growth but can also result in unexpected food
safety problems. Thus, understanding the pressure-resistant characteristics
of microorganisms can facilitate the selection of marker
strains and pasteurization settings to achieve pasteurization goals
effectively.
High pressure are currently being established to determine
the pressure-time combinations necessary for many species of
pathogenic microorganisms. Comparisons of pressure resistance
among vegetative food-borne pathogens revealed that strains of
E. coli O157:H7 were the most resistant so far encountered. When
defining pressure processing to be used in food preservation, it is therefore important to ensure that the pressure and exposure
times used is D-value of least 5 should be achieved of E. coli
O157:H7 strains by an adequate margin of safety. However, high
pressure alone are not particularly effective in killing bacterial
spores, high pressure processing designed to kill spores are most
often carried out with high temperatures. Although germinated
spores are generally much less resistance to high pressure
treatments, the major stumbling block to more widespread utilization
of high pressure for food processing is that high pressure
germination is not complete, and even multiple cycles of highpressure
treatment can leave some dormant spores untouched.
The effects of high pressure on bacterial spores is presently not
fully understood, it will be necessary to do a more detailed high
pressure destruction kinetics study on bacterial spores, taking in
to account various pressure processing conditions. We hope that
this review provides basic knowledge of the pressure-resistant
characteristics of microorganisms and the primary mechanisms
that cause microbial death under various HPP conditions
(including biochemical metabolic effects, changes in genetic
material, and damage to cell structures). However, the establishment
of additional scientific theories behind HPP and its
practical processing application parameters is required, because
many commercial applications demand detailed evaluations of
sanitation and safety, economic value, and product form, among
other factors.