Agriculture Reference
In-Depth Information
behave differently, even in the same conditions (Eby et al.
2009
). Morones
et al. (
2005
) showed that the amount of silver ions released from silver
nanoparticles in their experiment was too low to account completely for their
toxicity.
Inorganic nanoparticles can be easily incorporated into the polymers to create
antimicrobial nanocomposites (Althues et al.
2007
), and that is one of the biggest
advantages over molecular antimicrobials. AgNPs can be engineered to remain
potent antimicrobial agents for long periods of time (Roe et al.
2008
) due to their
controlled release properties. And this makes nanosilver/polymer composites very
attractive materials for food packaging. The antimicrobial activity of the silver
nanocomposites is dependent on different factors that affect the Ag
+
release rate
like the degree of polymer crystallinity, filler type (silver zeolites or silver
nanoparticles), hydrophilicity of the matrix, and particle size.
Other nanomaterials have also been found to have antimicrobial properties, like
TiO
2
(Hamal et al.
2010
), MgO (Huang et al.
2005
), Cu and CuO (C´rdenas
et al.
2009
), ZnO (Bajpai et al.
2010
), Cd (Xie et al.
2011
), chitosan
(Lu et al.
2010
), and carbon nanotubes (Kang et al.
2009
).
7.2.3
Intelligent Packaging Materials
Intelligent packaging refers to those packages that allow the monitoring of the
conditions and the quality of the content of the package from the production line to
the consumer. Intelligent packaging can be related to the inclusion of smart labels in
the package that give information about the physicochemical properties of the food
or the interior of the package, like temperature, pH or different gases, chemical
contaminants, and pathogens concentrations. Although a very promising area of
research related to food packaging, most of the research on nanosensors or assays
for analytes related to food is still in the early stages of development.
7.2.3.1 Monitoring Changes in pH
Martins et al. (
2012
) recently postulated the possible use of platinum nanoparticles
as pH sensor for intelligent packaging. They were able to measure changes of pH by
the difference in absorbance of a solution of Pt nanoparticles with sizes between
250 and 500 nm stabilized with thioglycolic acid and dispersed in water. The
fraction of cluster population depended on the pH of the aqueous solution, and
there was a memory effect in the response of the Pt nanoparticles to pH variations.
This memory effect is not desirable for other applications but is an interesting
feature for smart labels for food packaging. They suggest using an additional
control sensor giving a reliable value of the actual pH, and if absorbance values
read from the control and from the Pt nanoparticle sensor were different, it would be
