Respiration of grains

1. LECT. No. 3
RESPIRATION OF GRAINS

2. • Introduction
• Chemical Reaction
• Respiration Process
• Heating
• Control Methods

3. Introduction
• The process whereby organisms convert matter into
energy.
• Basic process of life
• In plant material, it principally involves oxidation of
sugar to CO2 and water accompanied by release of
energy.

4. Introduction
• Grain is biological material.
It is living thing.
It breathes.
• Each kernel gets oxygen from the air and
burns food from its endosperm.
• Process gives off heat, water, and carbon
dioxide.

5. • Important is
 Loss of principal food reserves
 Need for O2
 Disposition of CO2
 Disposition of energy
Plant or plant parts provide substrate
Air furnishes O2
Air receives CO2 & energy

6. • Respiration in plants, animals and fungi involves
1. the absorption of oxygen,
2. the disappearance of food substances within the
cells,
3. excretion of CO2. and
4. the liberation of heat energy.

8. Chemical Reaction
• During respiration sugars of the grain or of the food
are oxidised to carbon dioxide and water according
to following equation:
Food material + Oxygen  Carbon dioxide + Water + Heat 
(energy)
kcal
O
H
CO
O
O
H
C 677
6
6 2
2
2
6
12
6 




9. Respiration of grain produces heat, water and
carbon dioxide.
1% dry matter loss in 1 tonne grain produces:
• 6 kg of water increases m.c. by 0.6%.
• 37.600 kcal increasing temperature by 6.5°C,
(if heat is not transmitted).

10. Respiration: Process of Life activity
– consumes dry matter from the grain.
– Besides grain respiration, Heat and carbon
dioxide are also formed by the activity of
bacteria, fungi and insects.
– Heat and water resulting from the respiration of
the grain as well as the activity of bacteria, fungi
and insects cause an increase in moisture content
and temperature, which again increases the life
activity.

11. Heating
– Cereal grains have low thermal conductivity of
about 0.15 W/m0C.
– This is due to porosity present in grains.
– 45 – 60% of grain mass consists of inter-granular
air.
– Hence, grain mass is a good insulator of heat.

12. Thermal conductivity
• Thermal conductivity is the quantity of heat
transmitted through a unit thickness in a
direction normal to a surface of unit area,
due to a unit temperature gradient under
steady state conditions.
• 1 W/(m.K) = 1 W/(m.oC)

13. Thermal Conductivity
No. Material Thermal Conductivity
W/m-K
1 Copper 401
2 Gold 310
3 Aluminum 250
4 Brass 109
5 Iron 80
6 Carbon Steel 54
7 Stainless Steel 16
8 Brickwork, common 1
9 Water 0.58
10 Alcohol 0.17

14. Thermal Conductivity
No. Material Thermal Conductivity
W/m-K
11 Hydrogen (gas) 0.168
12 Grain 0.15
14 Straw slab insulation, compressed 0.09
15 Freon (liquid) 0.07
16 Cork 0.07
17 Cotton Wool insulation 0.029
18 Oxygen (gas) 0.024
19 Nitrogen (gas) 0.024
20 Air, athmosphere (gas) 0.024
21 Carbon dioxide (gas) 0.0146

15. Heating
– As a result the generation of even small quantity
of heat within a mass of grain can cause a
serious increase in localized temperatures.
– Similarly, cold ambient surround a mass of warm
grain will not cause useful cooling
– unless the grain is ventilated.

16. • It is well known that inadequately dried and
cooled grain causes grain heating resulting in
respiration rates which render the mass
thermally unstable.
• Insects respire and produce heat. Consequently,
if a nucleus of insects find an area within a grain
mass which is suitable for reproduction localized
heating will occur.
• As the temperature rises, insects breed more
rapidly generating more heat. The process is
therefore self-accelerating.

17. • Eventually the grain gets so hot that the adult
insects move into cooler areas around the
periphery of the hot spot.
• The immobile immature stages of the insects
remain in the hot spot where they are killed
by temperatures which may rise to 400C.

18. • Equilibrium relative humidity of warm air is higher than that
of cold air.
• In order that equilibrium can be maintained, the warm air
must, therefore, absorb moisture from the grain mass.
• If temperature gradient exists within the grain mass,
‘Convention Currents will be created’.
• They will cause the warm air to rise from the hot spots.
• On reaching the cooler upper layer of grain, the air will be
cooled to a temperature which is below its dew point.
• This will cause condensation which may result in sprouting
of the grain and the development of mould.

23. Control Methods
• Control methods for fungi, insects and other
associated organisms in stored grain include
1. Lowering temperature
2. Lowering moisture content,
3. Limiting the O2 content or
4. Increasing the CO2 content of the atmosphere and
5. Treating with chemicals.
• Time is an important factor because the control
becomes more complicated as the length of storage
period increases.

24. • Moist grain with a high life activity, producing
water and heat, form ideal conditions for
fungi, insects and mites, and
• leads to a fast deterioration if it is not kept
under powerful ventilation or dried
immediately.

26. • Respiration:
• The process whereby organisms convert
matter into energy.
• Basic process of life
• In plants, respiration principally involves
oxidation of sugar to CO2 and water
accompanied by release of energy. However,
other substances, such as organic acids and
proteins, also outer the respiratory chain.

27. • In standard storage conditions,
• If RH – 14%, & Temp. < 200
a quintal of wheat breathes very little and
expels less than 150 mg of CO2/day
But in the presence of O2 if RH is increased by 4 to
5%
Release of CO2 may becomes 100 times greater

28. • Respiration increases at an accelerating rate when
the grain moisture content rises above 10 to 12%.
• It also rises as the temperature rises. Rate of
respiration of wheat (15% M.C.) at 55 0C is 25 times
higher than that at 35 0C.