Food Protection with Modified Atmospheres
353
Table 14–3 Some Examples of Gas and Water Vapor Transmission Properties of Film Used
for Food Packaging
∗
Transmission Properties
Comment
1. OTR 7.8–9.3 ml/m
2 /24 hours/37.8
◦ C/70% RH
Extremely high barrier
2. a. OTR 8 ml/m
2 /24 hours/4
◦ C/100% RH
Extremely high barrier
b. CO 2 TR 124 ml/m
2 /24 hours/100% RH
c. WVTR 18.6 g/m
2 /24 hours/37
◦ C/100% RH
3. OTR 10 ml/m
2 /24 hours/22.8
◦ C/0% RH
4. a. OTR 32 ml/m
2 /24 hours/23.9
◦ C/50% RH
High barrier
b. CO 2 TR 47 ml/m
2 /24 hours/23.9
◦ C/70% RH
c. WVTR 0.8–1.8 g/m
2 /24 hours/23.9
◦ C/70% RH
5. OTR 52 ml/m
2 /24 hours/1 atm/25
◦ C/75% RH
High barrier
6. OTR 154 ml/m
2 /24 hours
Whirl-Pak bags
7. OTR 300 ml/m
2 /24 hours/25
◦ C/1 atm/100% RH
Commonly used for vacuum packaging
8. OTR 1,000 ml/m
2 /24 hours/25
◦ C/1 atm/90% RH
Essentially aerobic
9. OTR 6,500 ml/m
2 /24 hours/23
◦ C/0% RH
Highly permeable
10. OTR 7,800–13,900 ml/m
2 /24 hours
WVTR 240–419 g/m
2 /24 hours
PVC film
11. OTR 6,500 ml/m
2 /24 hours/23
◦ C/0% RH
Stretch-wrapped film
∗ OTR = oxygen transmission rate; RH = relative humidity; WVTR = water vapor transmission; PVC = polyvinyl
chloride.
80–90
◦ C water. A method that is suitable for raw meats consists of simply squeezing out the excess air
from a pouch followed by heat sealing. In addition to retarding aerobic spoilage organisms, vacuum
packaging minimizes product shrinkage, and retards both fat oxidation and discoloration. Gas and
water vapor transmission properties of some plastics used to vacuum-pack foods are listed in Table
14–3. In general, CO 2 permeability of such films is always higher than for O 2 by a factor of around 2 to 5.
Modified Atmosphere Packaging
Overall, MAP is a hyperbaric process that consists of altering the chamber or package atmosphere
by flushing with varying mixtures of CO 2 , N 2 , and/or O 2 . The initial gas concentration cannot be
readjusted during storage. Two types of MAP are recognized.
29
1. In high-O 2 MAP, up to 70% of O 2 along with about 20–30% CO 2 and 0–20% N 2 may be used.
Growth of aerobes is slowed but not suppressed by the moderate concentration of CO 2 . This
method is suitable for the packaging of red meats, as the high level of O 2 will aid in maintenance
of the red color. With time, the gas composition may be expected to change.
2. In a low-O 2 MAP system, O 2 levels may be as high as 10% while CO 2 is maintained in the
20–30% range with N 2 added as necessary.
Equilibrium-Modified Atmosphere
Equilibrium-modified atmosphere (EMA) packaging is achieved by flushing a gas-permeable pack
with gas, or sealing the pack without alteration. EMA is used for fresh fruits and vegetables.
76
353
Table 14–3 Some Examples of Gas and Water Vapor Transmission Properties of Film Used
for Food Packaging
∗
Transmission Properties
Comment
1. OTR 7.8–9.3 ml/m
2 /24 hours/37.8
◦ C/70% RH
Extremely high barrier
2. a. OTR 8 ml/m
2 /24 hours/4
◦ C/100% RH
Extremely high barrier
b. CO 2 TR 124 ml/m
2 /24 hours/100% RH
c. WVTR 18.6 g/m
2 /24 hours/37
◦ C/100% RH
3. OTR 10 ml/m
2 /24 hours/22.8
◦ C/0% RH
4. a. OTR 32 ml/m
2 /24 hours/23.9
◦ C/50% RH
High barrier
b. CO 2 TR 47 ml/m
2 /24 hours/23.9
◦ C/70% RH
c. WVTR 0.8–1.8 g/m
2 /24 hours/23.9
◦ C/70% RH
5. OTR 52 ml/m
2 /24 hours/1 atm/25
◦ C/75% RH
High barrier
6. OTR 154 ml/m
2 /24 hours
Whirl-Pak bags
7. OTR 300 ml/m
2 /24 hours/25
◦ C/1 atm/100% RH
Commonly used for vacuum packaging
8. OTR 1,000 ml/m
2 /24 hours/25
◦ C/1 atm/90% RH
Essentially aerobic
9. OTR 6,500 ml/m
2 /24 hours/23
◦ C/0% RH
Highly permeable
10. OTR 7,800–13,900 ml/m
2 /24 hours
WVTR 240–419 g/m
2 /24 hours
PVC film
11. OTR 6,500 ml/m
2 /24 hours/23
◦ C/0% RH
Stretch-wrapped film
∗ OTR = oxygen transmission rate; RH = relative humidity; WVTR = water vapor transmission; PVC = polyvinyl
chloride.
80–90
◦ C water. A method that is suitable for raw meats consists of simply squeezing out the excess air
from a pouch followed by heat sealing. In addition to retarding aerobic spoilage organisms, vacuum
packaging minimizes product shrinkage, and retards both fat oxidation and discoloration. Gas and
water vapor transmission properties of some plastics used to vacuum-pack foods are listed in Table
14–3. In general, CO 2 permeability of such films is always higher than for O 2 by a factor of around 2 to 5.
Modified Atmosphere Packaging
Overall, MAP is a hyperbaric process that consists of altering the chamber or package atmosphere
by flushing with varying mixtures of CO 2 , N 2 , and/or O 2 . The initial gas concentration cannot be
readjusted during storage. Two types of MAP are recognized.
29
1. In high-O 2 MAP, up to 70% of O 2 along with about 20–30% CO 2 and 0–20% N 2 may be used.
Growth of aerobes is slowed but not suppressed by the moderate concentration of CO 2 . This
method is suitable for the packaging of red meats, as the high level of O 2 will aid in maintenance
of the red color. With time, the gas composition may be expected to change.
2. In a low-O 2 MAP system, O 2 levels may be as high as 10% while CO 2 is maintained in the
20–30% range with N 2 added as necessary.
Equilibrium-Modified Atmosphere
Equilibrium-modified atmosphere (EMA) packaging is achieved by flushing a gas-permeable pack
with gas, or sealing the pack without alteration. EMA is used for fresh fruits and vegetables.
76