Environmental Engineering Reference
In-Depth Information
Gaspermeabilityrequirementsofthepackaging(forO
2
,CO
2
,andhumidity)
depend on the contents being preserved. High permeability to humidity
is essential in packaging of fresh produce or bread to avoid condensation
of water inside the package potentially causing mold growth. Hygroscopic
foods such as sugars, milk powder, and dessert mixes on the other hand
require low-permeability packaging to avoid moisture ingress that can cake
the free-flowing powders. With fresh produce, good gas exchange (for
respiration) is critical to maintain their freshness. Specialized products
(cooked food and some cheeses, for instance) use modified atmosphere
packaging (MAP) where some of the air in the package has been replaced
by N
2
or CO
2
and where gas environment must be maintained within the
within the package (Hotchkiss and Banco, 1992) possibly due to the
presenceofcarbonicacidfromreactionofCO
2
withwater.Plasticpackaging
can address these diverse permeability specifications economically with the
available wide range of plastic resins and their combinations. Oxygen
transmission rate (OTR) and water vapor transmission rate (WVTR) of
different plastics in common units are tabulated in
Table 8.2
.
