Biomedical Engineering Reference
In-Depth Information
For example, a particular food may be relatively stable within a certain range of water
activity corresponding to water contents according to its moisture sorption isotherm.
If stored at the same temperature in an environment where the ambient humidity
would cause a gain or loss of water, the food product could reach a critical water
content level at which the rate and extent of deterioration results in excessive loss of
quality. This condition has been defined as the endpoint of shelf life. Resistance
offered by the packaging material to water vapor transmission serves to slow the rate
at which water is gained or lost from the product, which in turn influences the nature
and rate of degradative processes, and thereby controls the shelf life.
Physical and barrier properties of a packaging system can also have an important
influence on the shelf life of the packaged food product. The environment to which
the product is exposed during distribution and storage can in turn influence shelf
life directly by promoting deteriorative reactions in foods, or by causing changes in
the performance of the packaging material itself that permit deteriorative reactions
to proceed. A discussion of these environmental influences is necessary to understand
the critical role that packaging can play in shelf life stability. Additional influences
such as the physical, chemical, and biochemical characteristics of the product are
discussed in more detail elsewhere in this topic.
P ACKAGING M ATERIALS
An important function of a package is to act as a barrier between a product and the
external environment, but the requirement for protection will depend largely on
product characteristics. In order to enhance shelf life, control of local environmental
conditions should be met by the packaging layer in closest contact with the food.
Another function of packaging is to protect the product during transit, and this often
requires the use of secondary or tertiary layers of packaging with different physical
properties. A brief review of the various properties of general packaging material
categories follows. More specific and in-depth information on these materials and
their manufacture can be found in other sources. 1,9
Glass
Glass is a traditional packaging material that has retained its high quality image for
selected packaging applications. Glass containers permit excellent clarity so that the
product is visible, and are resealable, recyclable, and sometimes reusable. Glass
packages are valued for being relatively inert and providing a total barrier to water
vapor and gas transmission, except at the container closure. However, compared to
other forms of food packaging, glass is heavy, brittle, and has low thermal shock
resistance. Light transmission can be a significant disadvantage for light sensitive
foods packaged in clear containers, but can be reduced through the use of colored
glass. For example, light in the wavelength region of ultraviolet to 500 nm can
catalyze oxidative reactions in beer; however, amber glass is used commonly for
single-serve beer packaging because it effectively absorbs most light in this spectral
region. 10 It is also important to note that most packaged food is protected from light
by secondary packaging, such as corrugated boxes, during distribution and storage.
 
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