Agriculture Reference
In-Depth Information
substances that absorb ethylene, oxygen, carbon dioxide, moisture, flavors, or odors
and other materials that release antioxidants, carbon dioxide, antimicrobial agents,
or flavors (Vermeiren et al.
1999
).
7.2.2.1 Oxygen Absorbers/Scavengers
Oxygen (O
2
) is directly or indirectly responsible for the degradation of many foods.
Direct oxidation reactions are responsible, for example, of rancidity of vegetable
oils and browning of fruits. Food deterioration can also be produced by indirect
action of O
2
due to food spoilage by aerobic microorganisms. Very low O
2
levels
inside the packaging can be maintained by incorporating O
2
scavengers, which is
useful for several applications.
Xiao-e et al. (
2004
) described the photocatalytic activity of nanocrystalline
titania: UV illumination of nanocrystalline TiO
2
/polymer films in the presence
of excess organic hole scavengers resulted in the oxygen removal in a closed
environment. According to the authors, it can be used for packaging many
oxygen-sensitive products, but a major flaw is the UVA light requirement.
In another approach, different thermoplastic polymers (PET, PP, FEP, LLDPE,
and nylon) have been infused with metal and metal oxide nanoparticles, and it has
been discovered that films containing less than 1 wt% Pd and Pt nanoparticles were
active as oxygen scavengers and reduced the oxygen flux by two orders of magni-
tude (Yu et al.
2004
).
7.2.2.2 Antimicrobials
Different kinds of nanoparticles have been used to create antimicrobial food
packaging. Among them, nanosilver is the most widespread (Rai et al.
2009
),
even with commercialized items already in the market. The antimicrobial proper-
ties of silver have been known since ancient times where wine and water were
stored in silver vessels. Silver has many advantages over other antimicrobial agents.
It has a broad spectrum and is toxic to numerous strains of fungi, bacteria, algae,
and some viruses, with varying degrees of toxicity. In its elemental form, it is shelf
stable for long periods of time. Silver can also be easily incorporated into many
different materials such as plastics and textiles, making it especially useful for food
packaging applications.
Despite the known antimicrobial properties of bulk silver, the mechanism of its
activity is still unknown. There is also some controversy about the manner in which
silver nanoparticles (AgNPs) are toxic to bacterial cells: some postulate that the
activity comes from the Ag
+
ions detached from the surfaces of AgNPs which will
act by the same mechanisms as conventional silver antimicrobials (Lok et al.
2007
).
However, some research shows that silver nanoparticles are more toxic than the
equivalent amount of dissociated silver ion (Limbach et al.
2007
). It has also been
demonstrated that particles of different shapes, sizes, or other characteristics may
