TERM
PAPER
ON
THE PRESENT DAY
SITUATION OF POST-HARVEST LOSS OF FRUITS AND
VEGETABLES IN NIGERIA
JUNE 2009
1.0 INTRODUCTION
Nigeria is blessed with a tropical climate
which favours the production of root and tuber crops as well as fruits and
vegetables, majority of which are staple foods. The United Nations General Assembly resolution of September
1975 focused world-wide attention on the problem of post-harvest food losses
and called for concerted action to reduce these losses in the following words:
"The further reduction of post-harvest food losses in developing countries
should be undertaken as a matter of priority with a view to reaching at least a
50% reduction by 1985. All countries and competent international organizations
should co-operate financially and technically in the effort to achieve this objective".
The
above statement vividly describes the problem mankind has always had to
preserve food supply after he has produced it. The loss of foods in the
post-harvest system is not new; it has always been a problem for mankind.
Fruits and vegetables are the major source of
vitamins A and C, a good source of calcium and iron, and they supply part of
the requirements for a number of other minor nutrients. The total annual production of
horticultural crops in developing countries was put at 620 million tones which
is 85% of the cereal production. This surpasses the relative world average where
horticultural crop production is only 70% of the cereal production. These high
production figures indicate the important role that horticultural crops play in
the economy of developing countries.
In
addition, horticultural crops add variety, enjoyment and a sense of
satisfaction with the diet because of their appealing colour, flavours and
textures.
On
all of these counts- nutrition, economics, acceptability- horticultural crops
play a major role in Nigeria, amply justifying the increasing urgency to asses
the extent of post harvest losses. This will help in conserving/ managing food
supply and possibly alleviate hunger and malnutrition.
1.1 Definition of terms
Since
the ramifications of food and the food supply spread right through society it
is necessary to define exactly what is meant by the term "post-harvest
loss". The working definition given below is based on that developed by Bourne
(1977).
"POST-HARVEST"
begins at the moment of separation of the edible commodity from the plant that
produced it by a deliberate human act with the intention of starting it on its
way to the table. The post-harvest period ends when the food comes into the
possession of the final consumer
"LOSS"
means any change in the availability, edibility, wholesomeness or quality of
the food that prevents it from being consumed by people.
VEGETABLE
The term "vegetable" is
usually used to designate the tender edible shoots, leaves, fruits and roots of
plant that are eaten whole or in part, raw or cooked, as supplement to starchy
foods and meat.
The definition
of the word is traditional rather than scientific, however, and therefore the
usage of the word is somewhat arbitrary and subjective, as it is determined by
individual cultural customs of food selection and food preparation (Wikipedia;
encyclopedia).
Vegetable include a broad variety of
edible plant parts which can be eaten cooked (potatoes, pepper) or raw (lettuce,
tomatoes) during the principal course of a meal. They can be grouped into 3
main categories namely:
·
Seeds and pods e.g. beans, pea, and corn
·
Bulbs, root and tubers e.g. onion,
carrot
·
Flowers, stems and leaves e.g.
cauliflower, celosia and Amaranthus.
FRUITS
These are seed-bearing structure
of a flowering plant. A fruit is actually a ripened ovary, a component of the
flower’s female reproductive structure. Depending on the type of plant, the
mature ovary may form a juicy, fleshy fruit, such as a mango, apple, plum, or
blueberry. Or it may develop into a dry fruit, such chestnut, or almond. Grains
of wheat, corn, or rice also are considered dry fruits.
Certain foods commonly termed vegetables, including tomatoes,
squash, peppers, and eggplant, technically are fruits because they develop from
the ovary of a flower.
1.2 Major Fruits and Vegetables Cultivated
In Nigeria Based On Ecological Distribution
Transition zone: Egg
plant, Orange, Banana, Pineapple, Mango, Citrus, Avocado, Corchorus, Talinum,
Melon, Celosia.
Rainforest
zone: Cauliflower.
Rainforest zone:
Cauliflower, Melon, Coffee, Melon, Watermelon, Orange, Pineapple, Mango,
Citrus, Onion, Amaranth spinach, Pumpkin, Bitter leaf, Cashew, Banana, Yam,
Pawpaw, Waterleaf, Cucumber, Okra, Tomato, Cocoa.
Sahel Savanna: Amaranthus,
Okra, Lettuce, Pumpkin, Watermelon, Onion, Pepper, Cowpea, Carrot.
Guinea Savanna: Cauliflower,
Coffee, Tomato, Pepper, Yam, Cassava, Cowpea, Roselle.
Sudan Savanna: Cauliflower,
Mango, Coffee, Onion, Carrot, Tomato, Pepper, Okra, Garlic.
1.3 Seasons of production
Seasonal climatic variations prelude the continuous
production of any vegetable. Crops suitable for cool season variation include:
Lettuce, Cabbage, Potato, Onions, Lima beans, Garden pea.
Certain vegetables species are tolerant of wet condition provided surface
drainage is achieved. These include; water spinach, cabbage and cucumber will
tolerate wet soil and not inundation. Some
vegetables are well adapted to the north due to there low level of water
requirement e.g. Onion, Carrot. In fact, the variation of the consumption,
cultivation of the various vegetables is majorly determined by ecological
factors such as rainfall, sunlight duration e.t.
2.0 CAUSES OF POSTHARVEST LOSSES
There are so many causes for losses
in the post-harvest food chain that it helps to classify them into 2 groups
A. PRIMARY CAUSES OF LOSS are those
causes that directly affect the food. They may be classified into the
following groups
a. Biological. Consumption of food by
rodents, birds, monkeys and other large animals causes direct disappearance of
food. Sometimes the level of contamination of food by the excreta, hair and
feathers of animals and birds is so high that the food is condemned for human
consumption. Insects cause both weight losses through consumption of the food
and quality losses.
b. Microbiological. Damage to stored
foods by fungi and bacteria. Micro-organisms usually directly consume small
amount of the food but they damage the food to the point that it becomes unacceptable
because of rotting or other defects. Toxic substances elaborated by molds
(known as mycotoxins), cause some food to be condemned and hence lost.
c. Chemical. Many of the chemical
constituents naturally present in stored foods spontaneously react causing loses
of colour, flavour, texture and nutritional value. An example is the Mallard
relation' that causes browning and discoloration in dried fruits and other
product. There can also be accidental or deliberate contamination of food with
harmful chemicals such as pesticides or obnoxious chemicals such as lubricating
oil.
d. Biochemical reactions. A number of
enzyme-activated reactions can occur in foods in storage giving rise to off-flavours,
discoloration and softening. One example of this problem is the unpleasant
flavours that develop in frozen vegetables that have not been blanched to
inactivate these enzymes before freezing.
e. Mechanical. Bruising, cutting'
excessive pooling or trimming of horticultural products are causes of loss.
f. Physical. Excessive or insufficient
heat or cold can spoil foods. Improper atmosphere in closely confined storage
at times causes losses.
g. Physiological. Natural respiratory
losses which occur in all living organisms account for a significant level of
weight lose. A reduction in nutritional level and consumer acceptance may also
arise with these changes.
Microbiological, mechanical and physiological
factors cause most of the losses in perishable crops.
B. SECONDARY CAUSES OF LOSS are those
that load to conditions that encourage a primary cause of loss. They are
usually the result of inadequate or non-assistant capital expenditures,
technology and quality control. Some examples are:
1.
Inadequate harvesting, packaging and handling skills.
2. Lack of adequate containers for
the transport and handling of perishables.
3. Storage facilities inadequate to
protect the food.
4. Transportation inadequate to move the
food to market before it spoils.
5. Inadequate refrigerated storage.
2.1 Sites of losses
Losses may occur anywhere from the
point where the food has been harvested or gathered up to the point of
consumption. For the sake of convenience the losses can be broken down into the
following sub-headings:
a. Harvest. The separation of the
commodity from the plant that produced it.
b. Preparation. The preliminary
separation or extraction of the edible from the non edible portion.
c. Preservation is the prevention of
lose and spoilage of foods. For example, the sun-drying of fruit, the use of
refrigeration.
d. Processing
e. Storage
f. Transportation. All forms of
transportation are used to convey foods.
2.2 Extent of
losses
The extent of losses is highly variable
depending on a number of conditions. Stable foods such as cereal grains can be
stored in good condition for several years, whereas perishable foods such as
fruit and vegetables spoil quickly unless given special treatment such as
canning and freezing. The longer the time the food is stored the more
opportunity there is for losses of all kinds to occur.
In Nigeria losses may be fairly high
during harvesting because the agricultural machinery that is used to harvest
the crops leaves some of the commodity in the field and mechanically damages
some of it (That is any is available). However, harvest losses are usually
lower because most of the crop is hand picked. The amount of material rejected
is less because the expectation of quality and uniformity is generally lower
than for developed countries.
Pantastico (1977) pointed out that
post-harvest losses in developing countries often exceed production losses and
cites as an example the following figures for losses is the Philippines:
Crop
|
Production (m. tons)
|
Production Value ($)
|
Percentage Loss
|
Loss Value ($)
|
Fruits
|
2,763,443
|
403,909,220
|
28.1
|
113,498,490
|
Vegetables
|
1, 640, 541
|
248, 564, 310
|
42. 2
|
104,894,130
|
Total
|
4,403,984
|
652,473,530
|
_
|
218,392,620
|
2.3 Effects of the environment on
post harvest losses
The environmental conditions under
which foods are stored and processed have a major effect on the keeping quality
of the foods and the amount that is lost. The major environmental influences on
the keeping quality of foods in Nigeria are:
Temperature: In general, the higher the
temperature the shorter the storage life of horticultural products and the
greater the amount of lose within a given time, as most factors that destroy
the produce or lower its quality occur at a faster rate as the temperature
increases. Nigeria has temperature as high as 40C. Most of the fruits and
vegetables are produced in remote areas and are transported under this high
temperature. Hence the high coefficient of post harvests losses.
Humidity: There is movement of water vapour
between a food and its surrounding atmosphere in the direction towards
equilibrium water activity in the food and the atmosphere. Most fruit handlers
in Nigeria are quite aware of this but could not help situation in cases of
high quantity of commodity handing, giving a high damage.
2.4 EXTENT OF LOSS OF
FRUITS AND VEGETABLES.
Tomato
In Nigeria, studies in 1974 and 1975
showed that up to 21% of tomato fruit loss in the field with an additional 20%
rotted in transit and in the market. The losses in the field are caused by a
combination of several pests (Onesirosan and Fatunla 1976).
Olorunda and Aworh (1983) established
that mechanical damage account to a large extent for losses of tomato and
pepper and to a small extent of Onions transported from Northern Nigeria to
Southern Nigeria.
Cassava
The cassava roots have no natural
dormancy and are highly susceptible to deterioration. The physiological
deterioration, of which the symptoms are tissue discoloration, can commence as
soon as 24 hours after harvest.
Plantain and Banana
In Nigeria, the most evident
post-harvest losses are registered at the producer level in enclave sites
during the rainy season (N'da Adopo, 1993). These losses should be less than 35
percentage) in developing countries as previously estimated by FAO (1987).
According to Treche (1997), 69.4% of
plantains and other cooking bananas are used for human consumption while 8.0%
are used for animal feed. Post-harvest losses and transformed quantities in the
world are 11.5% and 11%, respectively.
2.5 NON GRAIN VEGETABLE LOSS IN LESS
DEVELOP COUNTRIES
Commodity production Estimated
loss
In “000 tones in %
Potatoes
26,909 5-40
Sweet potato 17,630 35-95
Carrot 577 44
Cassava 103,486 10
Yam 20,000
10-60
Onion
6,474 16-35
Tomatoes
12,755 20-50
Plantain
18,301 35-90
Cabbage
3,036 37
Banana 36,898 20-80
Papaya 931
40-98
Citrus 22,040
23-33
Avocado 1,020
43
Apples 3,677
14 .
Source: Adapted from National Academy of Science
(1978).
2.6
STRORAGE STRUCTURE AND MATERIALS.
1.
Sacks and nets: Sacks and nets are of various sizes, description, and materials
are in wide spread use for the domestic and regional marketing of any root
crops such as sweet potato, yam, carrot, pumpkins and fruits, including citrus.
Cheapness is the only advantage that sack as over other forms of packaging. It
occupies very little space itself; this gives some advantage to the shippers in
the regional trades. The lack of rigidity of sacks means that they offer no
support for produce and when stacked do not prevent compression of the produce.
2.
Basket: These are relatively cheap and are made from locally
available and readily renewable resources. Due to there spherical shape they
may be rolled around if they are too heavy to lift. The basket offers extremely
little protection to the protection to the produce when several baskets or
other containers are stacked on top of each other.
3.
Wooden crates: Widely used by the hawkers and traffickers in the
inter-island trade in fresh produce. There is no standard size and designs in
current use. Untreated wood easily become contaminated with decay organisms and
may be difficult to wash effectively. Rough surfaces of the wood may injure the
produce unless it is lined.
4.
Fiber board cartons: These are made of solid or comigated fiber board construction of various thickness and resilience
depending on the produce to be contained and the market to be supplied. Fiber
board cartons are not re-usable; they are easily damaged by water and rough
handling unless impregnated with wax.
5.
Plastic crates: These are manufactured to a wide variety of specifications.
They have a long life span allowing there use on a return for many journeys.
Storage of fruits and vegetables using evaporative cooling systems.
Ceramics pot fired at 600ºC have been used to evaporatively cool water
to about 15ºC below ambient temperature. The pot is a double walled container,
with the outer shell filled with water which cools the container and its content
by an evaporative process (see fig.1). Also local and cheap but effective
method of storage called “Portable evaporator coolant structure” developed by
Natural Stored product research institute (NSPRI) Lagos (see fig 2) Kuku 1985
as helped tremendously in keeping post harvest indices at a lower rate.
Picture s
Evaporative storage system
3.0 CONCLUSION
Nigeria has ample rainfall for the cultivation of all kinds of fruits
and vegetables, such as plantains, citrus fruits, sweet potato, cashew,
pumpkin, amaranths e.t.c. The country is
also blessed with water bodies to ensure all year round availability of these
crops.
We might as a consequence of all
these indices, be inclined to conclude that the basic ingredients for
achievement of self sufficiency of food production are in place. But factors of
post harvest loss among others prove this wrong.
Although, it is very difficult to quantitatively describe the actual
magnitude of loss due to post harvest wastages. It is however very clear that,
losses recorded especially during the season of production of the various
fruits and vegetables are considerablely high, well above 50%. A number of
authors (Hall, 1968, Agboola, 1980, Ene & Okoye,1981, Ene 1986) drew
attention to the urgent necessity to match every effort at increasing crop
production with equal effort to save harvested crops from deterioration and
other post harvest losses. As such, the much desired increase in food availability
in Nigeria will be achieved.
