Biomedical Engineering Reference
In-Depth Information
containers and polymer fi lms. Many deteriorative reactions are catalyzed by light in
general and ultraviolet light in particular. Light may infl uence lipid oxidation, off-
fl avor generation, discoloration, and degradation of nutritionally important compo-
nents such as ribofl avin, beta-carotene, ascorbic acid and certain amino acids
( Bosset et al.
1994
). On the other hand, transparent packages allow consumers to
see the product through the package and judge on its quality by its appearance. This
is important for products like fresh meat, poultry, fruits and vegetables, confection-
ery, baked goods and thermally preserved foods in glass jars (e.g., fruits in syrup,
strained infant foods, etc.). A certain compromise between protection from light and
transparency may be achieved by using coloured plastic or glass.
Plastic packaging materials may be opaque, hazy (translucid) or transparent.
Plastic materials are rendered opaque by the incorporation of very fi ne solid parti-
cles of white or colored pigments into the melt. Haze or cloudiness is the result of
light scattering (diffraction) by the crystalline micro-regions of the polymer.
Amorphous plastics such as polycarbonate are clear (i.e. transparent). An inclusion
of UV fi lter in the transparent packaging fi lms has greatly reduced the above men-
tioned quality defects.
3.2.3
Mechanical Properties
The ability of a package to protect its contents against external forces depends on its
mechanical properties. In packaging technology, mechanical properties should be
considered and evaluated at the level of the packaging material, the formed empty
package, the product package assembly and the outer packages. The mechanical
strength of cans depends on the size, shape, thickness of the tinplate and geometric
pattern of the can. At equal tinplate thickness, cans with smaller diameters are
mechanically stronger. Frequently, the side walls of the can are beaded to increase
mechanical strength. Except for the integrity and stability of the closure, mechani-
cal strength is not an issue with glass. Relatively high output rates with minimal
breakage can be achieved with adequately designed handling and conveying equip-
ment, and with proper surface treatment to provide lubricity and prevent scratches.
Peelability, seal strength, extensibility, tear strength etc. are some of the important
mechanical properties for fl exible packaging materials.
3.2.4
Migration from the Package
Migration, i.e. the transport of potentially harmful substances from packaging mate-
rials into the packed food products is a serious concern for the industry and consum-
ers. Many factors infl uencing the migration of package components are: composition
of the packaging material, material conversion and processing conditions and the
food properties. The migration phenomena are now known for plastics and metal
