Chapter 19
Other Food Protection Methods
The methods presented in the previous six chapters are well established and in wide use throughout
the world. Presented in this chapter are some methods that are less widely used but which show promise
of being of greater importance in the future.
HIGH HYDROSTATIC PRESSURES (HHP, HPP)
The use of high pressure processing (HPP) or Pascalization to reduce or destroy microorganisms
in foods dates back to 1884.
11 In 1899, Hite successfully used hydrostatic pressures to improve the
quality of milk,
18 and in 1914 he demonstrated the susceptibility of fruitborne organisms to hydrostatic
pressures.
19 Thus, the utility of this process to control microorganisms and preserve foods has a long
history but only relatively recently has it received detailed study. The current interest is due apparently
to consumer demands for minimally processed foods, and to the lower cost and greater availability of
processing equipment. HHP treatments may be applied at room temperature, and with the exception
of some vegetables, shape, color, and nutrients of most foods are not affected. At least 10 HPP-treated
foods, including fruit pur´ ees, jams, fruit juices, and rich cakes, have been commercially available in
Japan since the early 1990s.
8
To carry out HPP, high hydrostatic pressures (HHP) are used, and one needs a suitable mechanical
chamber (steel cylinder) and pressure pumps to generate pressures of several hundred megaPascal
(MPa) (1 MPa = 10 atm; 100 MPa = 1 kbar). Come-up and come-down times for pressure are
important, and rates of 2–3 MPa/sec are not uncommon. After the food is placed in suitable containers
and sealed, the food packs are placed in the cylinder containing a low-compressibility liquid such
as water. Pressure is generated with a pump, and it may be applied continuously (static) or in an
oscillatory manner. For the latter, 2–4 pressure cycles may be applied with varying holding periods
for each cycle. In a study on the inactivation of Zygosaccharomyces bailii, continuous and oscillatory
treatments were compared and the latter was found to be the more effective.
38 With an initial inoculum
of about 1.6 × 10
6 colony-forming units (cfu)/ml, oscillatory treatments with holding times totaling
20 minutes at 276 MPa reduced the numbers to <10 cfu/ml (Figure 19–1). The cells were suspended
in Sabouraud’s glucose 2% broth with sucrose added to adjust water activity (a w ) to 0.98. In an
earlier study with spores of Geobacillus stearothermophilus, 10
6 spores/ml were destroyed after six
5-minute cycles (60 minutes total) at 600 MPa and 70
◦ C while with static and 800 MPa at 60
◦ C for
60 minutes, spores were reduced to 10
2 /ml.
15 By either method, the action is instant and uniform
throughout a container regardless of size, and HPP is equally effective for both liquid and solid foods.
457
Other Food Protection Methods
The methods presented in the previous six chapters are well established and in wide use throughout
the world. Presented in this chapter are some methods that are less widely used but which show promise
of being of greater importance in the future.
HIGH HYDROSTATIC PRESSURES (HHP, HPP)
The use of high pressure processing (HPP) or Pascalization to reduce or destroy microorganisms
in foods dates back to 1884.
11 In 1899, Hite successfully used hydrostatic pressures to improve the
quality of milk,
18 and in 1914 he demonstrated the susceptibility of fruitborne organisms to hydrostatic
pressures.
19 Thus, the utility of this process to control microorganisms and preserve foods has a long
history but only relatively recently has it received detailed study. The current interest is due apparently
to consumer demands for minimally processed foods, and to the lower cost and greater availability of
processing equipment. HHP treatments may be applied at room temperature, and with the exception
of some vegetables, shape, color, and nutrients of most foods are not affected. At least 10 HPP-treated
foods, including fruit pur´ ees, jams, fruit juices, and rich cakes, have been commercially available in
Japan since the early 1990s.
8
To carry out HPP, high hydrostatic pressures (HHP) are used, and one needs a suitable mechanical
chamber (steel cylinder) and pressure pumps to generate pressures of several hundred megaPascal
(MPa) (1 MPa = 10 atm; 100 MPa = 1 kbar). Come-up and come-down times for pressure are
important, and rates of 2–3 MPa/sec are not uncommon. After the food is placed in suitable containers
and sealed, the food packs are placed in the cylinder containing a low-compressibility liquid such
as water. Pressure is generated with a pump, and it may be applied continuously (static) or in an
oscillatory manner. For the latter, 2–4 pressure cycles may be applied with varying holding periods
for each cycle. In a study on the inactivation of Zygosaccharomyces bailii, continuous and oscillatory
treatments were compared and the latter was found to be the more effective.
38 With an initial inoculum
of about 1.6 × 10
6 colony-forming units (cfu)/ml, oscillatory treatments with holding times totaling
20 minutes at 276 MPa reduced the numbers to <10 cfu/ml (Figure 19–1). The cells were suspended
in Sabouraud’s glucose 2% broth with sucrose added to adjust water activity (a w ) to 0.98. In an
earlier study with spores of Geobacillus stearothermophilus, 10
6 spores/ml were destroyed after six
5-minute cycles (60 minutes total) at 600 MPa and 70
◦ C while with static and 800 MPa at 60
◦ C for
60 minutes, spores were reduced to 10
2 /ml.
15 By either method, the action is instant and uniform
throughout a container regardless of size, and HPP is equally effective for both liquid and solid foods.
457