Biomedical Engineering Reference
In-Depth Information
TABLE 4.3
Representative Oxygen (O 2 ) and Carbon Dioxide (CO 2 )
Permeabilities of Various Food Packaging Polymers at
23 to 25°C and 75% Relative Humidity
Permeability
(cc.mm.m -2 .day -1 .atm -1)
O 2
Polymer
CO 2
Ethylene vinyl alcohol copolymer (EVOH)
27 mol% ethylene
0.012 a
0.016 b
44 mol% ethylene
0.028 a
0.078 b
Polyvinylidene chloride (PVDC)
0.04
0.098
Polyethylene terephthalate (PET)
1.88
9.44
Polyvinyl chloride (PVC)
1.96
7.88
Nylon 6, unoriented
2.6
4
Polypropylene (PP), biaxially oriented
59
216
High density polyethylene (HDPE)
73
228
Low density polyethylene (LDPE)
196
984
a @ 20°C.
b @ 20°C, 65% relative humidity.
Adapted from Brown. 14
Light
The exposure of foods to ambient lighting in food production and storage, display
lighting in retail stores, and sunlight can lead to a wide variety of adverse effects
which reduce shelf life, such as the development of off-flavors in dairy products or
rancidity in fats and oils. The light-induced or photodegradation of foods is also a
factor in the destruction of vitamins. Although the mechanisms of many of these
effects have been studied extensively, research into the use of appropriate packaging
to reduce or eliminate light-induced changes to improve shelf life is limited; some
exceptions are cited below.
Dairy products are adversely affected by exposure to light, but the most critical
effects vary depending on the specific product. The light-induced quality deteriora-
tion of milk includes the development of off-flavors and losses of vitamins A, C,
and riboflavin. 25,26 The extent of the deterioration is dependent on light source,
wavelength, intensity, exposure time, temperature, and therefore, also on the light
barrier (or transmission) properties of the packaging material. Numerous studies,
including deMan 27 and Nelson and Cathcart, 28 have been carried out to determine
the most detrimental wavelengths of light and the light transmission properties of
milk containers. Wavelengths in the 350 to 550 nm range were found to be the most
harmful to milk quality. Paperboard cartons were shown to be opaque to wavelengths
below 450 nm; however, unpigmented blow-molded polyethylene milk containers
allowed 60 to 80% light transmission in the 400 to 700 nm range. Light transmission
 
 
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