Packaging Considerations - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 131

TABLE 4.1
Oxygen and Water Vapor Transmission Rates of Some
Biaxially Oriented Polypropylene (OPP) Films

OTR a WVTR b

OPP type (cm 3 /m 2 day atm) (g/m 2 day)

Clear, 30 µm <1500 <5.5

Acrylic coated 2 sides, 30 µm 650 4.0

Metallized, 30 µm <120 <0.8

PVDC coated 2 sides, 28 µm 16 5.0

Metallized/acrylic coated, 21 µm 1-2 1.0-1.5

a 23 ± 2°C and 90% RH.
b 38°C and 90% RH.
OTR = oxygen transmision rate; WVTR = water vapor transmission rate.
Adapted from Reilly and Man. 11

process can be used to design packages for specific products, such as fresh lettuce
mix, where the permeation of carbon dioxide out of a package would be considered
desirable.
Plasticfilms and containers vary greatly in the degree of protection they can
provide as a food packaging material. For many flexible packaging applications,
mono-layer materials have been largely replaced by multi-layer laminates, coated
films, and metallized film structures with greatly improved barrier properties against
light and oxygen. Manufacturing techniques such as coextrusion, lamination, and
metallization can be employed to produce multi-layer structures with barrier prop-
erties designed to meet specific product shelf life requirements. For example, met-
allized biaxially oriented polypropylene (OPP) film is commonly used for packaging
potato chips which require a good barrier to oxygen and light (to prevent oxidative
rancidity), and to water vapor (to prevent moisture uptake and to maintain crispness).
Whilefilm thickness plays an important role in water vapor and oxygen transmission
rates of OPP films, metallization and/or coatings with additional barrier materials
such as polyvinylidene chloride (PVDC) and acrylic polymers can greatly enhance
the barrier properties of films, as shown in Table 4.1 for OPP.

E NVIRONMENTAL F ACTORS

The climatic environment (e.g., moisture, oxygen, light, temperature, aromas) as
well as the physical distribution and storage environment (e.g., shock, vibration,
compressive loading) are major extrinsic factors involved in the numerous deterio-
rative reactions and physical damage that can lead to losses in food quality and
decreased shelf life. Details of specific deteriorative reactions and their mechanisms
have been described by Fennema and Tannenbaum. 12
The chemical deterioration of packaged foods is largely due to transfers of
oxygen, water vapor, aromas, and contaminants between the internal environment