Agriculture Reference
In-Depth Information
Retort pouches consist of multilayered materials. The
main material commonly used is polypropylene (PP) (e.g.,
cast polypropylene [CPP] film, oriented polypropylene
[OPP]), because it is resistant to high temperature and pres-
sure under thermal processing conditions, and also is low
in cost. Other materials commonly used are PET, of which
the most common type is crystalline PET (CPET), which
has higher temperature resistance than PET. PET also of-
fers strength and toughness. High-barrier materials such
as aluminum foil (Al), ethylene vinyl alcohol (EVOH),
poly(vinylidene) chloride (PVdC), and nylon are also used
in multilayer materials for extended shelf life products. Ad-
hesive layers are used in multilayer materials, and the safety
of these adhesives is another critical concern. Materials
used for retort pouches, for example, include PET/Al/CPP
and PET/Al/Nylon/PP, while transparent retort pouches are,
for example, OPP/EVOH/PP, OPA/EVOH/CPP, PET/OPA/
CPP, PET/OPA/CPP, and AlO
x
/PET/OPA/CPP (Robertson,
2006).
Retort pouches are made in various forms, including
four-sided sealed pouches, three-sided sealed pouches, and
stand-up pouches. Other retortable packaging include plas-
tic or metal trays with peelable lids, laminated paper cans
with peelable lids, and plastic cans. Sealing and seal in-
tegrity are key factors in food processing, especially in
thermal processing using a retort. The tray and lid should
be made of the same type of plastic for enhanced sealability.
that are high barriers to oxygen include ethylene vinyl al-
cohol (EVOH), polyvinyl alcohol (PVOH), nylon 6 (0%
RH), Nylon MXD6, PET, and so on (Robertson, 2006).
Of these materials, EVOH, PVOH, and Nylon 6, how-
ever, are sensitive to water vapor. They are to be buried
within high water vapor barrier materials such as polyethy-
lene (PE) or polypropylene (PP) in the multilayer struc-
tures. In the past decade, stand-up plastic pouches have
been increasingly used for dried and dehydrated fruit prod-
ucts. Stand-up pouches offer attractive shelf display, con-
venience for handling and distribution, and generally low
cost as compared to glass and metal containers. Pouch prod-
ucts once open have limited storage life. Reclosable device
may be employed with the pouch for extending storage life
of products.
Tropical and subtropical fruits are also commonly made
into candied fruits, which are traditional products of many
countries. Major quality changes of candied fruits are due to
moisture gain (or sometimes loss) and the Maillard reaction.
Therefore, packaging requirements for candied fruits are
mainly to protect the products from moisture using a high
moisture barrier such as PE or PP. Some candied fruits
are rich in lipid content, such as coconut candied fruits.
These types of products also require a high oxygen barrier
to protect the products from lipid oxidation, which leads to
rancidity and off-flavor.
In addition, many other fruit products are moisture and/or
oxygen sensitive, for example, durian and jackfruit chips.
These products require a high barrier to both moisture and
oxygen to protect the products from crispness loss
and rancidity, which could result from both lipid oxidation
and hydrolytic oxidation. Therefore, similar to other dried
products, fruit chips are commonly packaged in compos-
ite cans, aluminum foil pouches, metalized plastic-based
pouches, and multilayer plastic pouches. Shelf life predic-
tion models are helpful tools in packaging material selec-
tion to obtain desired shelf life under economical concerns.
Packaging of dried and dehydrated fruit products
Water activity (
a
w
) is a physical property of food that is di-
rectly related to microbiological growth and spoilage. Low-
ering water activity is extensively used in food preservation.
This can be accomplished by reducing water, as in drying
and dehydration, or by adding solutes, as in concentrates.
Dried and dehydrated fruit products tend to absorb mois-
ture during storage, primarily resulting in aggregation, tex-
ture loss, and mold growth. Therefore, the most important
packaging requirement for this type of product is a mois-
ture barrier property. Additionally, oxygen and water are
involved in many chemical reactions, as well as in micro-
bial growth, which all lead to quality changes and spoilage
of food products. The amount of oxygen has a significant
effect on the stability of most products. Accordingly, dried
and dehydrated fruit products often require packaging with
a high oxygen barrier property.
Packaging materials that offer high-barrier properties to
both water vapor and oxygen are glass and metal. Plas-
tics have a wide range of permeability to oxygen and
water vapor. Multilayer materials are often used for food
packaging in order to obtain intended shelf life. Plastics
Packaging of frozen fruits
Major problems of frozen fruits include weight loss and
freezer burn. The latter occurs due to sublimation of wa-
ter vapor from the surface of the products. Freezer burn
has a significant effect on a product's appearance, and ad-
ditionally results in weight loss. Packaging requirements
to reduce these problems are the use of high moisture bar-
rier materials. In addition, packaging should protect against
light, as it accelerates deterioration. For that reason, opaque
materials are used. Moreover, the glass transition tempera-
ture (
T
g
) of polymeric packaging materials is a significant
factor for frozen fruits, as the products are stored at low
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