1. Chapter 3. Factor that contribute to grain post-
harvest losses
 A complex interplay of various factors contributes to the losses that occur in the
post-production grain loss.
 These elements can be classified as follows:
1. Biological and microbiological
2. Biochemical and chemical
3. Environmental and climatic or physical factors
4. Mechanical and technical
5. Socio-economic.
 As these factors impact one another, they ought not be treated or analyzed
separately.
 For example, climatic conditions (rain, temperature, humidity level, etc.) affect
 the physiological conditions of plants in the field or of the grain stored,
 As well as the degree of infestation by fungi, molds and other pests.

2.  These comprise all losses due to pests of any sort which are capable of attacking
undamaged grain (primary pests) as well as damaged grain (secondary pests).
 Insects, mites, rodents and birds fall in this category.
 Losses can be of both qualitative and quantitative nature,
 As food is consumed, damaged or contaminated by pests, especially during the storage
period.
 Several species of fungi (moulds, yeasts) also attack grains, some of them producing
mycotoxins that can be detrimental to humans and animals (such as aflatoxin in
groundnuts and maize).
3.1. Biological and microbiological factors

3. 3.1.1. Insect
 Insects are the major causes of post harvest grain losses.
 They penetrate the kernels and feeding on the surfaces and the endosperm.
 They remove selectively the nutritious part of the food and encourage the
development of bacteria and increase the moisture content of the food.
 Insect infestation will eventually lead to other storage problems.
 They give off moisture which can cause grain moisture contents to increase
enough to create a mold problem.
 Mold activity will in turn raise temperatures and result in an increased rate of
insect reproduction.
 Greater numbers of insects create more moisture, and the cycle is repeated at an
ever increasing rate.
 Insects also cause quality deterioration through their excreta as they consume.
 Insects are generally not a problem in grain stored for less than 10 months or a
year if the grain is at its safe moisture and low temperature of storage.

4. 3.1.1. Insect….
 Insects are usually the most serious storage pests.
 However, grain attacked by insects may still be eaten, unlike mould damaged grain,
which may be completely unusable.
 Nevertheless, insect damage reduces the quality of the grain and therefore the market
price.
 Storage insect pests are mainly beetles or moths.
 Beetle adults are usually found crawling over the surface of grains while adult moths,
if not resting on surfaces, are often found flying close to the store.
 Most damage is caused by immature (larval) stages, which mostly develop inside the
grain.
 Among all insects that attack stored products, weevils are very important:
 Sitophilus oryzae L. (Rice weevil).
 They attack cereals like rice and cereal products such as paste, flour and biscuits
 Sitophilus zeamais (Maize weevil).
 They attack maize, sorghum and other cereals

5. 3.1.1. insect
 Insect pests that attack stored grains can be divided into two types:
 primary pests, capable of attacking and breeding in previously undamaged
grains; and
 secondary pests that can only attack and breed in grains that have already
been damaged or
 grain that has been processed into flour or a similar product.
 Primary pests are very common in farm stores soon after harvest.
 In fact, they can occur in the plant once it has reached maturity in the field.
 Secondary pests tend to be most common once the grain has been damaged by
primary pests and
 Therefore are found after grain has been stored for several months.

6. 3.1.1. Insect…
 The most common primary insect pests of cereals are the weevils, Sitophilus
species.
 However, throughout much of Africa the larger grain borer, Prostephanus
truncatus, has become the most important pest of stored maize in recent years.
 Smaller grains, such as rice, millet and wheat, are commonly attacked by the
lesser grain borer, Rhyzopertha dominica.
 Only one moth is found commonly in grain stores, Sitotroga cerealella, the
Angoumois grain moth.
 It is frequently found in stores of cob maize, especially soon after harvest.
 The most common secondary pests of cereals and cereal products are Tribolium
species;
 T. castaneum, the red flour beetle is most prevalent in tropical and subtropical
areas, and
 T. confusum, the confused flour beetle is most common in more temperate
climates.

7. 3.1.1. Insect…
 Pulses are attacked by a family of primary pests, the Bruchidae or bruchids.
There are three common species:
 Acanthoscelides obtectus, the bean beetle, Zabrotes subfasciatus, the bean
weevil and Callosobruchus maculatus, the cowpea beetle.
 The first two mostly attack beans, particularly of the Phaseolus family, such
as common beans, haricot beans and lima beans,
 whereas Callosobruchus attacks small grain pulses such as lentils, grams and
cowpeas.

8. 3.1.2. Rodent
Three species of rodents are major pest of stored products:
 Rattus rattus (Black rat)
 Rattus norvegieus (Brown rat)
 Mus musculus (House mouse)
 Rats and mice damage storage containers, eat some of the stored produce, carry some
away to their nests and spoil much more with droppings, urine and hairs.
 They usually spoil more than they actually eat.
 They chew through bags allowing produce to spill out.
 It is important to remember that rodents are also carriers of disease, like plague, rat-
bite fever, and Lassa fever.
 Rodents are very good climbers, they can swim and can jump very effectively.
 They can easily gain access to most traditional grain stores because the materials
used for store construction provide little or no barrier.
 Rodents can chew holes in baskets and woodwork of stores and burrow through mud
floors and walls to get at stored produce.
 Only stores constructed from metal, brick or concrete are likely to protect stored
produce against rodents.

9. 3.1.2. Rodent…
Rat climbing

10. 3.1.3. Bird
 Some species of birds commonly feed on stored grain.
 Birds can consume large amounts of grain.
 They also contaminate the grain with their droppings and feathers.
 Damage and loss of stored grain can be reduced by preventing birds from
entering the store.
 The store should be kept in good condition and the entrance or door to the
store kept closed.
 The area around the store and compound should be kept clean as birds are
attracted by spilled grain.
 Losses caused by birds can be avoided by preventing their access to the stored
commodities.

11. 3.1.4. Fungi (Molds )
 Molds are growths that develop inside and on the surface of grains that have not been
dried properly or become wet during storage.
 They can be recognized as white, grey, black or green discoloration on the grain
surface.
 Other signs of the presence of mold are:
dustiness of grain;
caking of grain;
feed refusal by animals for no apparent reason;
a bad musty (mouldy) smell;
darkening of feed grain.
 Eating moldy grain has led to severe illness and even to death in several countries.
 Poisoning can cause cancers and can affect most of the organs of the body but
especially the stomach, kidneys, liver, and brain.
 Consumption of moldy grain may also make illnesses such as HIV/AIDS worse.

12. 3.1.4. Fungi (Mold)…
 There are two important types of storage molds,
 Aspergillus and Penicillium.
 Another common mould is Fusarium, which attacks
the plant in the field
 but, if the moisture content of the grain remains
high, may be carried over into the store after
harvest.
 All of these moulds produce harmful mycotoxins.
 The most common mycotoxin includes
 Aflatoxin
 Ochratoxin
 Fumonisin

Fusarium ear rot
Aspergillus ear rot

13. Factors that affect mold growth
 Moisture content of the grain; molds require water for growth, so if the crop is well dried
(below 13% for cereals and 7% for groundnuts), molds will not be able to grow.
 Climatic conditions; hot and humid conditions promote mold growth.
 Under such conditions, extra attention must be paid to drying the crop well.
 Field damage caused by insects, birds, rodents, and poultry (molds can quickly infect
grain through holes and cracks made by pests);
 Plant stress caused by drought, infertile soil and even untimely or excessive fertilizer
application (allows plants and seed to crack and become exposed to invading molds and
insects);
 Repeated planting of a crop in the same field may increase the risk of infection by mold;
 poor handling at harvest, during drying, threshing and transportation can cause damage to
grain, rendering it susceptible to attack by mold spores; and
 insect infestation in store (insect respiration produces water, which raises the moisture
content of the grain allowing molds to develop).

14. 3.1.5. Bacteria
 Bacteria prevalence to the stored durable crops may be low.
 They may, however, invade already damaged portion of the crop products
during storage and their multiplications.

15. 3.1.6. Metabolic activities
• Cereal grains are living materials and their normal chemical reactions produce heat
and chemical reactions by products.
• Heat is also generated by insects, mites and micro organisms, which if presented in
large number may lead to a significant rise in temperature of stored products.
• Under aerobic condition the complete combustion of a typical carbohydrate can be
represented by the following equation:
C6H12O6 + 6O2 6CO2+6H2O + 677.2Kcal
• There are two types of losses during metabolic processes:
a. The loss due to grain being converted by micro organism to carbon dioxide and
water.
b. The other loss occurs when the grain (entirely or as individual kernels) rejected.

16. 3. 2. Biochemical and chemical factors:
 Some of the chemical elements naturally present in stored commodities
provide the bases for loss of
Nutritional value,
Flavor,
Texture and
Color, for example through enzyme-activated reactions.

17.  Physical factors or abiotic factor such as
 oxygen,
 moisture,
 relative humidity, and
 temperature.
 Initial Grain Condition have a major impact on the storability of grain
 Physical factors influence the conditions for insect multiplication and mold
growth during grain storage, which eventually affects the storability of the grain.
 High humidity levels and temperatures can trigger an alteration of certain
biochemical processes such as oxidation and fermentation that can lead to a
deterioration of the grain in storage.
 These processes can also be altered by the concentration of certain substances
contained in the air surrounding the grain, such as oxygen, carbon dioxide or
nitrogen.
3.3. Environmental and climate (physical) factors:

18. ⚫ Temperature and moisture (store and grain) are responsible for the accelerating or
delaying biochemical processes within grain (especially the "breathing" of the
grain) which exhibits the origin of grain degradation
⚫ Different biochemical changes of grain due to infestation will also induce excessive
heating.
⚫ Furthermore, they have a direct influence on the speed of development of insects
and microorganisms (moulds, yeasts and bacteria).
⚫ Stored products pests breed within the temperature range of about 15-42°C but the
most important pest species breed within 18-38°C.
⚫ Within this range the optimum temperature range falls between 25-33°C.
⚫ The conditions beyond the minimum and maximum will either result in cold or
heat stress.
3.3.1. Temperature and moisture

19. ⚫ Temperature and humidity both are inter-related (higher the temperature, the
lower must be the moisture of the grain).
⚫ Most of the stored grain pest species breed faster under the humid condition,
typically 60-80 % which in term of grain moisture content is roughly
equivalent to 13-15 %.
⚫ At higher humidity, the mould growth will result.
⚫ Generally drier the condition (grain and store), less will be the pest
infestation.
⚫ If grain moisture content is too high, even the best aeration equipment and
monitoring management will not keep the grain from spoiling - it only delays
the inevitable.
⚫ All micro-organisms, including molds, require moisture to survive and multiply.
⚫ If the moisture content in a product going in to store is too low, microorganisms
will be unable to grow provided that the moisture in the store is also kept low.
3.3.1. Temperature and moisture…..

20. 3.3.2. Initial Grain Condition
 Grain quality will not improve during storage. At best, initial quality can only
be maintained.
 To help assure that only high quality grain goes into storage, the following is
recommended:
 Clean around the storage site. Remove any old grain, grass, weeds, and
other debris.
 Remove all traces of old grain from the storage and harvesting and
handling equipment.
 Properly adjust the combine (harvesting, threshing and handling
equipment) to minimize grain damage.
 Clean the grain as it is put into the storage, preferably using a rotating grain
cleaner.
 Cool the grain to the prevailing outside air temperature (that most usually
occurs) as soon as it is put into the storage.

21. 3.3.3. Low oxygen content
⚫ Like grain and micro-organisms, insects are living organisms that need oxygen.
⚫ Storage of grain in places that are low in oxygen causes
 the death of insects,
 cessation of development of micro-organisms, and
 blockage, or slowing down, of the biochemical processes of grain degradation.
⚫ This favours the conservation of grain, but may affect its germinating power.

22. 3.4. Mechanical factors
 The different farm operations that are carried out manually or
mechanically
 harvesting,
 drying,
 shelling,
 threshing,
 cleaning,
 bagging,
 transportation, etc.)
 can cause damage to the grain, which then becomes more
vulnerable to enzyme-mediated chemical changes and to attack
by insects and other pests.

23. 3.4.1. Effect of Harvesting on grain post harvest loss
 Harvesting timing and method (mechanical vs. manual) are two critical factors dictating
the losses during the harvesting operations.
 A large amount of losses occurs before or during the harvesting operations, if it is not
performed at adequate crop maturity and moisture content.
 Too early harvesting of crop at high moisture content increases the drying cost, making
it susceptible to
 Mold growth, and Insect infestation, resulting in a high amount of broken grains and
low milling yields.
 Leaving the matured crop un-harvested results in high shattering losses, exposure to
birds and rodents attack, and losses due to natural calamities (rain, hailstorms)
 Most of the harvesting is performed manually in the developing countries, which is a
highly labor intensive and slow process.
 Labor shortages, results in delays in the harvesting and subsequently large losses.

24. 3.4.1. Effect of Harvesting on grain post harvest loss..
 African producers harvest grain crops once the grain reaches physiological maturity
(moisture content is 20-30%) (FAO, World Bank, 2011).
 At this stage the grain is very susceptible to pest attacks. Poor farmers sometimes
harvest crops too early due to food deficiency or the desperate need for cash.
 In this way, the food incurs a loss in nutritional and economic value, and may get
wasted if it is not suitable for consumption.
 Quality cannot be improved after harvest, only maintained; therefore, it is important
to harvest at the proper maturity stage and at peak quality.
 Clearly, the higher the moisture contents of the grain at harvest time, the greater the
risks of losses from molds, insects and germination.
 On the other hand, the longer the grain remains in the field (to further the drying of
the product), the greater the risks of losses from spontaneous fall of grain or
 From attacks by birds, rodents and other pests.

25. 3.4.2. Effect of Threshing and shelling on grain post
harvest loss
 The purpose of the threshing process is to detach the grain from the panicles.
 The process is achieved through rubbing, stripping, or impact action, or using a
combination of these actions.
 The operation can be performed manually (trampling, beating), using animal power,
or mechanical threshers.
 Manual threshing is the most common practice in the developing countries.
 Grain spillage, incomplete separation of the grain from chaff, grain breakage due of
excessive striking, are some of the major reasons for losses during the threshing
process.
 Delay in threshing after harvesting of crop results in significant quantity and quality
loss, as the crop is exposed to atmosphere, and is susceptible to rodents, birds, and
insect attack
 As in the case of harvesting, lack of mechanization is the major reason for this delay
that causes significant losses.
 High moisture accumulations in the crop lying in the field may even lead to start
mold growth in the field.

26. • Losses during threshing may occur due to:
a) Incomplete threshing (grain remains on the straw);
b) Direct damage (breakage) to the grain or weakening of the seed coat, which leads to
grain that will be more susceptible to pests in storage; or spillage and scattering during
the process; and
c) consumption of grains by animals used for trampling purposes.
 Qualitative losses due to grain contamination with soil, animal droppings, and urine are
equally as important as quantitative losses.
 Threshing loss of cereals is minimized by
 Preparing a good (smooth and adequately wide) threshing ground,
 Using muzzles for trampling animals to avoid eating of the crop,
 Collecting the droppings of animals before they fall on the threshing ground,
 Making sure that all grains are separated from the straw (a well-dried crop will
thresh well), and threshing as promptly as possible.
3.4.2. Effect of Grain Threshing and shelling on grain
post harvest loss..

27. 3.4.3. Effect Grain Cleaning on post harvest loss
 The cleaning process is performed after the threshing to separate whole grains
from broken grains and other foreign materials, such as straw, stones, sand,
chaff, and weed seed.
 Winnowing is the most common method used for cleaning in the developing
countries.
 Screening/sifting is another common method of cleaning, which can be
performed either manually or mechanically.
 Inadequate cleaned grains can increase the insect infestation and mold growth
during storage, add unwanted taste and color, and can damage the processing
equipment.
 A large amount of grains are lost as spillage during this operation, and grain
losses during winnowing can be as high as 4% of the total production.

28. 3.4.4. Effect of On-farm drying on grain post harvest loss
 Drying is often necessary to bring the moisture content of the grain to the
recommended level for storage, selling or consumption.
 The drying methods and climatic conditions during drying are main factors
which affects losses.
 If the grain is traditionally dried in the open air (yard, road, etc),
 The crop is exposed to proliferation of fungi, moulds and bacteria and soil
reducing its quality.
 The crop is also exposed to attacks of domestic animals and birds causing
qualitative and quantitative losses.
 Grains should be dried in such a manner that damage to the grain is minimized
and
 moisture levels are lower than those required to support mold growth during
storage (usually below 13-15%).

29. 3.4.5. Effect of transportation on grain post harvest loss
 During post-harvest operations, transport is involved on several occasions:
 harvested crop may need to be moved from the field to the threshing floor,
and
 from there to the farm storage area, and finally from the storage area to the
processing facilities and collecting markets.
 From those markets, crops may be transported by retailers to their shops or
transported by wholesalers over long distances to distant or foreign markets by
train, trucks, ships, etc.
 During these operations, which require multiple loading and unloading, spillage
or grain losses may occurred.
 In addition, transit losses may also occur because of damage to grain in trains,
trucks, or ships caused by time-bound deterioration.
 In long-distance transport, grain may also be attacked by insects, fungi and other
pests, similarly to what usually happens during normal storage.

30. 3.5. Socio-economic factors:
 These include the nature of the equipment and facilities used at the different
points of the chain,
 The way the different operations are carried out by the actors (production
practices),
 As well as the conditions in which production takes place. Regarding material
and equipment,
 Inadequate (or absent) storage infrastructure or the use of low-efficiency
technology
 Such as threshing equipment leading to a high percentage of damaged
grain) are examples of equipment-driven losses.
 Inadequate harvesting, packaging and handling skills are production practices
that have a bearing on losses

31.  Regarding production conditions, the legal environment through its imposition
of quality standards that can affect the retention or
 Rejection of food for human consumption is another socio-economic factor that
may explain losses.
 In addition, the economic environment such as low commodity prices may push
farmers to divert their production from food to feed markets or
 simply to increase storage time to wait for better market conditions, thereby
increasing the risk of pest infestation and related damages and losses.
3.5. Socio-economic factors…