Gas Barrier Properties of Biopolymerbased Nanocomposites: Application in Food Packaging - Advanced Materials for Agriculture, Food and Environmental Safety - page 373

food packaging are based on silver nanoparticles, whose antimicrobial
activity has been ascribed to dif erent mechanisms, namely: (a) adhesion
to the cell surface, degradation of lipopolysaccharides and formation of
“pits” in the membranes, largely increasing permeability; (b) penetration
inside bacterial cell, damaging DNA, and; (c) releasing antimicrobial Ag +
ions by dissolution of silver nanoparticles. Besides their antimicrobial
activity, silver nanoparticles have been reported to absorb and decompose
ethylene, which may contribute to their ef ects on extending shelf life of
fruits and vegetables [15].
Titanium dioxide (TiO 2 ) is widely used as a photocatalytic disinfect-
ing material for surface coatings. Titanium dioxide photocatalysis, which
promotes peroxidation of the phospholipids present in microbial cell
membranes, has been used to inactivate food-related pathogens. A TiO 2
powder-coated packaging i lm able to reduce E. coli contamination on
food surfaces has been developed; and the ei cacy of TiO 2 -coated i lms
exposed to sunlight to inactivate fecal coliforms in water has been dem-
onstrated. Metal doping improves visible light absorbance of TiO 2 , and
increases its photocatalytic activity under UV irradiation. It has been dem-
onstrated that doping TiO 2 with silver greatly improved photocatalytic
bacterial inactivation. h is combination was explored by Hulleman et al. ,
who have obtained ef ective antibacterial activity from a polyvinyl chloride
nanocomposite with TiO 2 /Ag+ nanoparticles [16].
Carbon nanotubes have also been reported to have antibacterial prop-
erties. Direct contact with aggregates of carbon nanotubes have been
demonstrated to kill E. coli , possibly because the long and thin nano-
tubes puncture microbial cells, causing irreversible damage and leakage
of intracellular material. On the other hand, there are studies suggesting
that carbon nanotubes may also be cytotoxic to human cells, at least when
in contact to skin, which would af ect people manipulating the nanotubes
in processing stages rather than consumers [17]. Anyway, once present in
the food packaging material, the nanotubes might eventually migrate into
food. h en, it is mandatory to know any eventual health ef ects of ingested
carbon nanotubes.

13.4.3 Detection of Gases Produced by Food Spoilage

Food spoilage is caused by microorganisms whose metabolism pro-
duces gases, which may be detected by several types of gas sensors which
have been developed to translate chemical interactions between parti-
cles on a surface into response signals. Nanosensors to detect gases are
usually based on metal oxides or, more recently, conducting polymer