Control by Novel Processing Technologies ◾ 521
◾ In general, Bacillus spores are less resistant than Clostridium spores to pressure treatment.
◾ Dormant and superdormant spores are more pressure resistant.
◾ 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°C–90°C
(140°F–194°F), a 5-log cycle inactivation is difficult to attain in 10 minutes. 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 pressures and high temperatures and a second cycle of repressurization can be used to produce commercially sterile food.
This is discussed later.
Molds, Yeasts, Viruses, and Parasites
Initial studies were conducted to develop pressurization parameters at ambient temperatures to
destroy yeasts and molds because of their ability to grow in low pH, low A W , high osmotic environments, and refrigeration temperatures 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 300–350 MPa for 10 minutes at ambient temperatures. Although a few pressure-resistant species and strains of these microbes have been found, treatment at 400 MPa at 40°C (104°F) 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
300–400 MPa at ambient temperature. However, it is necessary to validate this by research.
Application in Food Processing 5,13,14,26,27
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 40.1.
Antimicrobial applications to preserve foods are briefly discussed here. Books and reviews may be
consulted for information on other applications.
Antimicrobial applications have been studied to produce mostly pressure-pasteurization products although limited studies are now being conducted to produce commercially sterile products.
Pressure pasteurization is considered nonthermal because the foods are pressurized (≤700 MPa) at a
lower temperature range (15°C to <70°C) to mainly kill vegetative cells of microorganisms, whereas
pressure sterilization involves pressurization (≥700 MPa) at high temperatures (≥90°C or 194°F) to
◾ In general, Bacillus spores are less resistant than Clostridium spores to pressure treatment.
◾ Dormant and superdormant spores are more pressure resistant.
◾ 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°C–90°C
(140°F–194°F), a 5-log cycle inactivation is difficult to attain in 10 minutes. 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 pressures and high temperatures and a second cycle of repressurization can be used to produce commercially sterile food.
This is discussed later.
Molds, Yeasts, Viruses, and Parasites
Initial studies were conducted to develop pressurization parameters at ambient temperatures to
destroy yeasts and molds because of their ability to grow in low pH, low A W , high osmotic environments, and refrigeration temperatures 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 300–350 MPa for 10 minutes at ambient temperatures. Although a few pressure-resistant species and strains of these microbes have been found, treatment at 400 MPa at 40°C (104°F) 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
300–400 MPa at ambient temperature. However, it is necessary to validate this by research.
Application in Food Processing 5,13,14,26,27
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 40.1.
Antimicrobial applications to preserve foods are briefly discussed here. Books and reviews may be
consulted for information on other applications.
Antimicrobial applications have been studied to produce mostly pressure-pasteurization products although limited studies are now being conducted to produce commercially sterile products.
Pressure pasteurization is considered nonthermal because the foods are pressurized (≤700 MPa) at a
lower temperature range (15°C to <70°C) to mainly kill vegetative cells of microorganisms, whereas
pressure sterilization involves pressurization (≥700 MPa) at high temperatures (≥90°C or 194°F) to