PACKING AND PACKAGING TECHNOLOGY
A recent study by WFLO (funded by the Bill & Melinda
Gates Foundation) reported on many issues related to the use of poor quality
packages in Africa and India. The scientists field tested a variety of improved
packages, including plastic crates, liners for rough containers, and smaller
sized sacks, and found them all to be simple to use and cost effective. Read
the full report: "Appropriate Postharvest Technologies for SSA and South
Here are some more ideas for improved packing practices and
packaging materials that can reduce postharvest losses and improve incomes for
small-scale produce farmers, handlers and marketers:
PACKING PRACTICES AND PACKING MATERIALS
Throughout the entire handling system, packaging can be both
an aid and a hindrance to obtaining maximum storage life and quality. Packages
need to be vented yet be sturdy enough to prevent collapse.
If produce is packed for ease of handling, waxed cartons,
wooden crates or rigid plastic containers are preferable to bags or open
baskets, since bags and baskets provide no protection to the produce when
stacked. Sometimes locally constructed containers can be strengthened or lined
to provide added protection to produce.
Waxed cartons, wooden crates and plastic containers, while
more expensive, are cost effective when used for the domestic market. These
containers are reusable and can stand up well to the high relative humidity
found in the storage environment.
Adding a simple cardboard liner to a crate will make it less
likely to cause abrasion to produce.
Containers should not be filled either too loosely or too
tightly for best results. Loose products may vibrate against others and cause
bruising, while over-packing results in compression bruising. Shredded
newspaper is inexpensive and a lightweight filler for shipping containers (if
the ink used for newspaper print is non-toxic).
For small-scale handlers interested in constructing their
own cartons from corrugated fiberboard, Broustead and New (1986) provide
detailed information. Many types of agricultural fibers are suitable for
paper-making and handlers may find it economically sensible to include these
operations in their postharvest system. Corrugated fiberboard is manufactured
in four flute types - type B (1/8 inch in height, 47 to 53 flutes per inch;
with a basis weight of 26 lb per 1,000 ft2) is the most commonly used for
Whenever packages are handled in a high humidity
environment, much of their strength is lost. Collapsed packages provide little
or no protection, requiring the commodity inside to support all of the weight
of the overhead load. Packing is meant to protect the commodity by immobilizing
and cushioning it, but temperature management can be made more difficult if
packing materials block ventilation holes.
Packing materials can act as vapor barriers and can help
maintain higher relative humidity within the package. In addition to
protection, packaging allows quick handling throughout distribution and
marketing and can minimize impacts of rough handling.
Produce can be hand-packed to create an attractive pack,
often using a fixed count of uniformly sized units. Packaging materials such as
trays, cups, wraps, liners and pads may be added to help immobilize the
produce. Simple mechanical packing systems often use the volume-fill method or
tight-fill method, in which sorted produce is delivered into boxes, then vibration
settled. Most volume-fillers are designed to use weight as an estimate of
volume, and final adjustments are done by hand.
Ethylene absorber sachets placed into containers with
ethylene sensitive produce can reduce the rate of ripening of fruits, de-greening
of vegetables or floral wilting. Sachets can be purchased from internet based
Broustead, P.J. and New, J.H 1986. Packaging of fruit and
vegetables: a study of models for the manufacture of corrugated fibreboard
boxes in developing countries. London: TDRI. (for information contact NRI,
Central Avenue, Chatham Maritime, Kent, ME4 4TB, United Kingdom).
ILLUSTRATIONS OF IMPROVED PRACTICES
Temperature and Relative Humidity Control
Throughout the period between harvest and consumption,
temperature control has been found to be the most important factor in maintaining
product quality. Fruits, vegetables and cut flowers are living, respiring
tissues separated from their parent plant. Keeping products at their lowest
safe temperature (0 °C or 32 °F for temperate crops or 10-12 °C or 50-54 °F for
chilling sensitive crops) will increase storage life by lowering respiration
rate, decreasing sensitivity to ethylene gas and reducing water loss. Reducing
the rate of water loss slows the rate of shriveling and wilting, causes of
serious postharvest losses.
Keeping products too cool can also be a serious problem. It
is important to avoid chilling injury, since symptoms include failure to ripen
(bananas and tomatoes), development of pits or sunken areas (oranges, melons
and cucumbers), brown discoloration (avocados, cherimoyas, eggplant), increased
susceptibility to decay (cucumbers and beans), and development of off-flavors
(tomatoes) (Shewfelt, 1990). Cooling involves heat transfer from produce to a
cooling medium such as a source of refrigeration. Heat transfer processes include
conduction, convection, radiation and evaporation.
If a ready supply of electricity is available, mechanical
refrigeration systems provide the most reliable source of cold. Methods include
room cooling, forced-air cooling and evaporative cooling. A variety of portable
forced-air coolers have been designed for use by small-scale growers and
handlers (Talbot and Fletcher, 1993; Rij et al, 1979; Parsons and Kasmire,
1974). However, a variety of simple methods exist for cooling produce where
electricity is unavailable or too expensive. Some examples of alternative
systems (from Thompson in Kader, 1992) include night air ventilation, radiant
cooling, evaporative cooling, the use of ice and underground (root cellars,
field clamps, caves) or high altitude storage. Ice can be manufactured using
simple solar cooling systems, where flat plate solar collectors are used to
generate power to make ice, which is then used to cool produce (Umar, 1998).
Ice can be used either directly as package ice, to cool water for use in a
hydro-cooler, or as an ice bank for a small forced air or room cooling system.
Several simple practices are useful for cooling and
enhancing storage system efficiency wherever they are used, and especially in
developing countries, where energy availability may be limited and any savings
may be critical. Shade should be provided over harvested produce, packing
areas, for buildings used for cooling and storage and for transport vehicles.
Using shade wherever possible will help to reduce the temperatures of incoming
produce and will reduce subsequent cooling costs. Trees are a fine source of
shade and can reduce ambient temperatures around packinghouses and storage
areas. Light colors on buildings will reflect light (and heat) and reduce heat
load. Sometimes spending money will save money, as when purchasing lighting
equipment. High pressure sodium lights produce less heat and use less energy
than incandescent bulbs.
Another aspect to consider when handling fruits and
vegetables is the relative humidity of the storage environment. Loss of water
from produce is often associated with a loss of quality, as visual changes such
as wilting or shriveling and textural changes can take place. If using
mechanical refrigeration for cooling, the larger the area of the refrigerator
coils, the higher the relative humidity in the cold room will remain. It pays
however, to remember that water loss may not always be undesirable, for example
if produce is destined for dehydration or canning.
For fresh market produce, any method of increasing the
relative humidity of the storage environment (or decreasing the vapor pressure
deficit (VPD) between the commodity and its environment) will slow the rate of
water loss. The best method of increasing relative humidity is to reduce
temperature. Another method is to add moisture to the air around the commodity
as mists, sprays, or, at last resort, by wetting the store room floor. Another
way is to use vapor barriers such as waxes, polyethylene liners in boxes,
coated boxes or a variety of inexpensive and recyclable packaging materials.
Any added packaging materials will increase the difficulty of efficient
cooling, so vented liners (about 5 percent of the total area of the liner) are
recommended. The liner vents must line up with the package vents to facilitate
cooling of the produce inside. Vented liners will decrease VPD without
seriously interfering with oxygen, carbon dioxide and ethylene movement.
Storage of horticultural crops
If produce is to be stored, it is important to begin with a
high quality product. The lot of produce must not contain damaged or diseased
units, and containers must be well ventilated and strong enough to withstand
stacking. In general proper storage practices include temperature control,
relative humidity control, air circulation and maintenance of space between
containers for adequate ventilation, and avoiding incompatible product mixes.
Commodities stored together should be capable of tolerating
the same temperature, relative humidity and level of ethylene in the storage
environment. High ethylene producers (such as ripe bananas, apples, cantaloupe)
can stimulate physiological changes in ethylene sensitive commodities (such as
lettuce, cucumbers, carrots, potatoes, sweet potatoes) leading to undesirable
color, flavor and texture changes.
Temperature management during storage can be aided by
constructing square rather than rectangular buildings. Rectangular buildings
have more wall area per square feet of storage space, so more heat is conducted
across the walls, making them more expensive to cool. Temperature management
can also be aided by shading buildings, painting storehouses white or silver to
help reflect the sun's rays, or by using sprinkler systems on the roof of a
building for evaporative cooling. The United Nations' Food and Agriculture
Organization (FAO) recommends the use of ferrocement for the construction of
storage structures in tropical regions, with thick walls to provide insulation.
Facilities located at higher altitudes can be effective, since air temperature
decreases as altitude increases. Increased altitude therefore can make
evaporative cooling, night cooling and radiant cooling more feasible.
Underground storage for citrus crops is common in Southern China, while in
Northwest China, apples are stored in caves (Liu, 1988). This system was widely
used in the U.S. during the early pert of this century.
Certain commodities, such as onions and garlic, store better
in lower relative humidity environments. Curing these crops and allowing the
external layers of tissue to dry out prior to handling and storage helps to
protect them from further water loss.
The air composition in the storage environment can be
manipulated by increasing or decreasing the rate of ventilation (introduction
of fresh air) or by using gas absorbers such as potassium permanganate or
activated charcoal. Large-scale controlled or modified atmosphere storage
requires complex technology and management skills, however, some simple methods
are available for handling small volumes of produce.
Cool Storage Ideas
Here is a report on the construction of a simple Charcoal
Cool Storage Room that works via the principle of passive evaporative cooling.
No electricity is required, but a small fan can help improve effectiveness by
moving air more quickly through the cool room. A list of materials is provided,
and ideas for testing its effectiveness for lowering temperature are provided.
This kind of cool room works best when relative humidity is low, such as in
drier climates or during the dry season. You can download the report by
clicking on this link: Charcoal Cool Room Report.
Zero Energy Cool Chamber (ZECC)
Designed by Dr. S.K. Roy in
India in the 1980s, it has been field tested and redesigned over the past few
years to improve function. The ZECC can be constructed in various sizes (from
100 kg to 1 MT capacity) depending upon the volume of fresh fruits or
vegetables that you want to store. It is designed as a temporary on-farm
evaporative type cool storage chamber, and can be self-constructed of bricks
and sand. Here is the link to the presentation prepared by Dr. S.K. Roy in
2009: Zero Energy Cool Champer PPT.
Field clamp for root and tuber crops (developed by
Before storing root and tuber crops, sorting out diseased
units and curing the crop will heal harvest wounds and allow the periderm to
thicken and provide protection from water loss and diseases. Here is an
illustration of a simple curing practice that can be used for field curing for
2 to 5 days:
Illustration of Field Curing
Illustration of a Field Clamp