Fundamental Food Microbiology, Third Edition - Fuad Fathir

524 FUNDAMENTAL FOOD MICROBIOLOGY
• High concentrations of nonionic solutes and ionic solutes, low A w, and high pH
increase resistance.
• At a low pressure range (@300 MPa), some spores germinate and outgrow, and
can be killed by one or more physical and chemical antimicrobial agents.
Although in low-pH foods inactivation of spores is not necessary, it is necessary to
destroy (or prevent germination and growth) foodborne Bacillus and Clostridium
spores in high-pH foods. Most results indicate that even at 800 MPa and a pressurization
temperature of 60 to 90�C, a 5-log cycle inactivation is difficult to attain in
10 min. Similarly, inducing germination of spores at a lower pressure range and
then killing the germinated spores with a second cycle of pressurization does not
ensure a predictable reduction of spores to achieve commercially sterile foods. It
might be necessary to destroy some spores by a combination of parameters applicable
for a food type and then prevent growth of the surviving spores with a suitable
antimicrobial agent. This method is used in low-heat-processed meat and other food
products. A recent study has reported that a combination of high pressure and high
temperature and a second cycle of repressurization can be used to produce commercially
sterile food. This is discussed later.
3. Molds, Yeasts, Viruses, and Parasites
Initial studies were conducted to develop pressurization parameters at ambient temperature
to destroy yeasts and molds because of their ability to grow in low pH, low
A w, high osmotic environment, and refrigeration temperature in fruit juices, jams,
and jellies. In general, a 4- to 5-log cycle of most foodborne yeasts and molds
(including their spores) can be achieved by pressurizing at 300 to 350 MPa for 10
min at ambient temperature. Although a few pressure-resistant species and strains
of these microbes have been found, treatment at 400 MPa at 40�C or a second cycle
of pressurization eliminates them.
Almost no report is currently available on the pressure-induced destruction of
foodborne protozoa and parasites in food systems. Similarly, the effect of pressure
on the inactivation of foodborne pathogenic human viruses and bacteriophages of
lactic acid bacteria (and prions) is not known. The current opinion is that the
protozoa, parasites, and viruses will be destroyed by pressure at 300 to 400 MPa at
ambient temperature. However, it is necessary to validate this by research.
D. Application in Food Processing 3,6–10
Hydrostatic pressure is being studied for many applications in food processing,
including killing microorganisms. Applications can be divided into three groups:
novel product development, improving processing techniques, and antimicrobial
applications, as listed in Table 39.1. Antimicrobial applications to preserve foods
are briefly discussed here. Books and reviews may be consulted for information on
other applications. 3,8
Antimicrobial applications have been studied to produce mostly pressure-pasteurization
products, although limited studies are now being conducted to produce