Other Food Protection Methods
467
Among the disadvantages are that packages may not be equivalent to glass or metal containers in
preventing the permeation of oxygen, and the output is lower than that for solid containers.
A wide variety of aseptic packaging techniques now exists, with more under development. Sterilization of packages is achieved in various ways, one of which involves the continuous feeding of rolls
of packaging material into a machine where hot hydrogen peroxide is used to effect sterilization, followed by the forming, filling with food, and sealing of the containers. Sterility of the filling operation
may be maintained by a positive pressure of air or gas such as nitrogen. Aseptically packaged fruit
juices are shelf stable at ambient temperatures for 6–12 months or longer.
The spoilage of aseptically packaged foods differs from foods in metal containers. Whereas hydrogen
swells occur in high-acid foods in the latter containers, aseptic packaging materials are nonmetallic.
Seam leakage may be expected to be absent in aseptically packaged foods, but the permeation of
oxygen by the nonmetal and nonglass containers may allow for other types of spoilage in low-acid
foods.
MANOTHERMOSONICATION (THERMOULTRASONICATION)
When bacterial spores are simultaneously exposed to ultrasonic waves and heat, there is a reduction in spore resistance. The effect is greatest when the two treatments are simultaneous, although
some reduction in resistance occurs when ultrasonication is carried out just before heating. This
phenomenon has been studied by workers in Spain and designated manothermosonication (MTS) or
thermoultrasonication.
34 In addition to spores, MTS has been shown to be effective in reducing the
thermal resistance of the enzymes peroxidase, lipooxygenase, and polyphenol oxidase.
27 Manothermosonication employs a lethal temperature while manosonication employs a sublethal temperature.
In essence, these methods employ ultrasonic waves under pressure.
Manosonication (117 µm and 200 kPa) at 60
◦ C was tested on S. Senftenberg, and a 3-log cycle
reduction was achieved compared to a heat treatment at 60
◦ C, which effected only a 0.5-log cycle
reduction.
29
In an early study of the effect of MTS on heat resistance using quarter-strength Ringer’s solution, the
D at 110
◦ C of a B. cereus strain was reduced from 11.5 to ∼1.5 minutes, and that of a B. licheniformis
strain at 99
◦ C from 5.5 to 3 minutes.
6 In another study using whole milk and two strains of B. subtilis,
D values at 100
◦ C were reduced from 2.59 to 1.60 for one strain, and from 11.30 to 1.82 minutes
in another.
12,35 Comparable z values were 9.12–9.37 and 6.72–6.31, respectively. Ultrasonication was
carried out at 20 kHz and 150 W. The z value results seem to confirm the minimal effect that MTS
has on z values.
34
As to the possible mechanism by which the heat resistance of bacterial spores is reduced by ultrasonic
treatments, a study using G. stearothermophilus found that the ultrasonic treatment effected the release
of calcium, dipicolinic acid, fatty acids, and other low-molecular-weight components.
37 The effect of
this on spores was believed to lead to a modified hydration state and, thus, lowered heat resistance.
This would not explain the effect of MTS on enzymes.
REFERENCES
1. Alpas, H., N. Kalchayanaand, F. Bozoglu, and B. Ray. 2000. Interactions of high hydrostatic pressure, pressurization
temperature and pH on death and injury of pressure-resistant and pressure-sensitive strains of foodborne pahogens. Int. J.
Food Microbiol. 60:33–42.
467
Among the disadvantages are that packages may not be equivalent to glass or metal containers in
preventing the permeation of oxygen, and the output is lower than that for solid containers.
A wide variety of aseptic packaging techniques now exists, with more under development. Sterilization of packages is achieved in various ways, one of which involves the continuous feeding of rolls
of packaging material into a machine where hot hydrogen peroxide is used to effect sterilization, followed by the forming, filling with food, and sealing of the containers. Sterility of the filling operation
may be maintained by a positive pressure of air or gas such as nitrogen. Aseptically packaged fruit
juices are shelf stable at ambient temperatures for 6–12 months or longer.
The spoilage of aseptically packaged foods differs from foods in metal containers. Whereas hydrogen
swells occur in high-acid foods in the latter containers, aseptic packaging materials are nonmetallic.
Seam leakage may be expected to be absent in aseptically packaged foods, but the permeation of
oxygen by the nonmetal and nonglass containers may allow for other types of spoilage in low-acid
foods.
MANOTHERMOSONICATION (THERMOULTRASONICATION)
When bacterial spores are simultaneously exposed to ultrasonic waves and heat, there is a reduction in spore resistance. The effect is greatest when the two treatments are simultaneous, although
some reduction in resistance occurs when ultrasonication is carried out just before heating. This
phenomenon has been studied by workers in Spain and designated manothermosonication (MTS) or
thermoultrasonication.
34 In addition to spores, MTS has been shown to be effective in reducing the
thermal resistance of the enzymes peroxidase, lipooxygenase, and polyphenol oxidase.
27 Manothermosonication employs a lethal temperature while manosonication employs a sublethal temperature.
In essence, these methods employ ultrasonic waves under pressure.
Manosonication (117 µm and 200 kPa) at 60
◦ C was tested on S. Senftenberg, and a 3-log cycle
reduction was achieved compared to a heat treatment at 60
◦ C, which effected only a 0.5-log cycle
reduction.
29
In an early study of the effect of MTS on heat resistance using quarter-strength Ringer’s solution, the
D at 110
◦ C of a B. cereus strain was reduced from 11.5 to ∼1.5 minutes, and that of a B. licheniformis
strain at 99
◦ C from 5.5 to 3 minutes.
6 In another study using whole milk and two strains of B. subtilis,
D values at 100
◦ C were reduced from 2.59 to 1.60 for one strain, and from 11.30 to 1.82 minutes
in another.
12,35 Comparable z values were 9.12–9.37 and 6.72–6.31, respectively. Ultrasonication was
carried out at 20 kHz and 150 W. The z value results seem to confirm the minimal effect that MTS
has on z values.
34
As to the possible mechanism by which the heat resistance of bacterial spores is reduced by ultrasonic
treatments, a study using G. stearothermophilus found that the ultrasonic treatment effected the release
of calcium, dipicolinic acid, fatty acids, and other low-molecular-weight components.
37 The effect of
this on spores was believed to lead to a modified hydration state and, thus, lowered heat resistance.
This would not explain the effect of MTS on enzymes.
REFERENCES
1. Alpas, H., N. Kalchayanaand, F. Bozoglu, and B. Ray. 2000. Interactions of high hydrostatic pressure, pressurization
temperature and pH on death and injury of pressure-resistant and pressure-sensitive strains of foodborne pahogens. Int. J.
Food Microbiol. 60:33–42.