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Post harvest management practices


Post harvest management practices

Parboiled rice:

It is produced by process of soaking, pressure steaming and drying prior to milling. This helps the grain to absorb most of the vital nutrients from the husk.

  • Parboiling rice drives nutrients, especially thiamine, from the bran into the grain, so that parboiled white rice is 80% nutritionally similar to brown rice.
  • The starches in parboiled rice become gelatinized, making it harder and glassier than other rice. Parboiled rice takes less time to cook, and the cooked rice is firmer and less sticky.

Plate 1. Parboiled rice

Parboiling is a hydrothermal treatment of paddy. Parboiled rice is "par"-tially "boiled" (i.e. partially cooked rice). In other words parboiling means precooking of rice within the husk. Paddy is first hydrated, then heated to cook the rice and finally dried.

  • Cleanin             
  • Soaking
  • Steaming
  • Drying
  • Milling
  • Grading
  • Sorting

In general, three major steps in parboiling i.e., soaking, steaming and drying have a great influence on the final characteristics and quality of the parboiled rice.

1. Raw rice (paddy)

2. The vitamins and minerals in the outside husk.

3. In a vacuum the rice loses all theair contained in it. In the followingwarm water bath the nutrients start to become soluble and move out of the husk.

4. To move the nutrients out of the husk, but inside of the rice, the hot steam and air pressure is used (other way the nutrients would just get washed out into the water).

Parboiled rice vs boiled rice?

            Both are same. Boiled or Parboiled. Both the process is same. Once the harvesting is over, the grain with the husk is brought to the Rice Mill. Rice grains were dumped in a big cement slots and fill water. Then the slot is set to boil (electric) until the husk splits into two. After that, it is spread on the floor to get dried. Then they are processed in a machine which separates the husk / skin from the rice. Then the rice is sent to another machine for polishing. This is what is called parboiled / boiled rice.

TABLE 1 - Effect of parboiling method on thiamine content and protein

Treatment

Number of Samples

Degree of milling (%)

Thiamine (µg/g)

Protein (%)


Raw

Treated

Raw

brown

Treated

brown

Raw

milled

Treated

milled

Raw

milled

Treated

milled

Modified traditional(hot soak)

2

11.0

10.6

3.2

2.5

0.4

1.9

8.3

7.3

Lab. Method(hot soak) 121°C 10 min

2

11.6

12.0

3.8

3.2

0.6

2.9

9.0

8.6

US commercial parboiling

3

12.2

12.6

3.9

2.8

0.5

2.1

6.6

6.2

Heated-sand drying

2

10.5

10.2

3.7

3.6

0.6

1.8

8.2

7.8

LSD (%)

 

0.8

 

 

0.3

 

0.5

 

0.9

 

TABLE 2 - Nutritional properties of two milled rice, raw and parboiled

Rice type

Crude

protein

(%NX6.25)

Lysine

(g/16 8 N)

Balance data in five growing rats

 

 

 

True

digestibility

(% of N

intake)

Biological

value

(% of digested N)

Net protein

utilization

(% of N

intake)

Digestible

Energy (% of

intake)

IR480-5-9b

Raw

11.2

3.4

100.4

66.8

67.1

97.0

Parboiled 10 min

10.4

3.6

94.7

70.4

66.7

 

IR8 c

Rawd

7.7

3.6

96.2

73.1

70.3

96.6

Parboiled 20 min

7.2

3.7

89.7

78.1

70.0

95.2

Parboiled 60 min

7.4

3.5

88.6

79.5

70.4

94.7

LSD (5%)b

0.2

0.2

0.9

1.1

1.4

0.5

LSD (5%)b

0.2

0.2

0.9

1.1

1.4

0.5

  • Parboiling done at 121°C, properties at 14% moisture content
  • Eggum, Resumcci6n & Juliano, 1977.
  • Eggum et al., 1984.
  • Eggum & Juliano, 1973; Eggum, Alabata & Juliano, 1981

Storage

  • After-harvest ripening during storage is accompanied by a higher yield of total and head milled rice.
  • Stored rice expands more in volume and yields more flaky cooked rice with less dissolved solids in the cooking water than freshly harvested rice.
  • The exact mechanism of storage changes is not fully understood, but such changes occur in all starchy foods. In rice they occur mainly above 15°C.
  • The rice grain is very hygroscopic because of its starch content and equilibrates with the ambient relative humidity.
  • The safe storage moisture content is generally considered to be 14 percent in the tropics. Storage pests (insects and micro-organisms) and rodents cause losses in both quantity and quality of the grains. Gross composition is not affected by storage, but vitamin content decreases progressively.
  • Dehulling with rubber rollers minimizes bruising of the brown rice surface and improves the shelf-life of the dehulled grain.

Common Storage Pests of Rice

A. Insects

Insects in stored rice can be classified into four groups according to their feeding habits namely internal feeders, external feeders and scavengers.

1. Internal Feeders

These are insects whose larvae feed entirely within the kernels of the grain. These include rice weevil, angoumois grain moth and lesser grain borer.

1)      Rice Weevil : Sitophilos oryzae (Linnaeus)

Optimum conditions:

  • Temperature: 28°C
  • Relative humidity: 70%
  • Number of eggs:150
  • Life cycle: 35 days

Damage:

  • Adults and larvae feed on a wide variety of grains.
  • Female deposits a single egg in the grain by boring a hole inside.
  • The egg stays in the grain until it becomes an adult thus making the grain completely damaged.

 

 Angoumois Grain Moth: Sitatroga cerealella (Olivier) 

  • Eggs are laid on or near grain.
  • The white larvae bore into the kernels of the grain and feed on the inside.
  • When mature, the larvae eat its way to the outer portion of the grain, leaving only a thin layer of the outer seed coat intact.
  • Pupation takes place just under the seed coat.
  • They infest only the surface layer of bulk-stored grain, adults are unable to penetrate deeply.
 

Lesser Grain Borer : Rhyzopertha dominica (Fabricus)

Optimum conditions:

  • Temperature: 34°C
  • Relative humidity: 60-70%
  • No of eggs: 300-500
  • Life cycle: 20-84 days

Damage:

The eggs are laid in the grain mass and larvae may enter the kernels and develop within or, they may feed externally in the flour-like dust that accumulates from the feeding of the adults and their fellow larvae.

 

2. External Feeders

 External feeders are insects that feed from the outside of the grain even though they may chew through the outer coat and devour the inside.

1) Cigarette or Tobacco Beetle: Lasioderma serricorne (Fabricius)

 Life cycle: 6 to 8 weeks

Damage:
Feeds on books, flax tow, cottonseed meal, rice, ginger, pepper, dried fish, crude drugs, seeds, pyrethrum powder, and dried plants.

2)      Flat Grain Beetle :Cryptolestes pusillus (Schonherr)

The female places her eggs loosely in the grain mass. The larvae and adults are able to penetrate the seed coat of the undamaged grain.

 

3. Scavengers

Scavengers feed on the grain only after the seed coat has been broken either mechanically or by some other insect.

1)Saw-toothed Grain Beetle : Oryzaephilus surinamensis (Linnaeus)

Optimum Conditions:

  • Temperature 30-35°C
  • Relative humidity: 70-90%
  • Number of eggs: 150
  • Life cycle 20 days

Damage:

Eggs are usually laid, either singly or in small masses, in a crevice in the food supply but in items like flour, they are laid freely.

Management of storage insects

The management of stored grain pests should be done in a sequential and integrated manner. An effective pest control system involves

Harvesting, drying and storage

  • Grain must be dried to at least 14% moisture (wet basis) and seed grain should be dried to12% moisture before storage.
  • Harvesting and threshing at the correct stage of maturity (20-25% moisture content)
  • When sun drying, the grain should be spread in thin layers, 2-5cm, and turned every 1-2 hours and not exposed to temperatures above 42oC.
  • Grain stores must have a damp proof floor and have waterproof walls and roof.
  • Where grain is to be stored in bags, the bags should be stacked on pallets at least 50cm away from the walls.
  • Hermetic storage systems have proved to be an effective means of storing grain.

Disinfesting the storage system

Storage containers, structures, bags and equipment can be treated with

  1. Malathion (50EC) at 5ml/20l of water @20ml/m2
  2. Fenitrothion (50EC) at 5ml/l water @20ml/m2
  3. Deltamethrin (2.5% WP) at 1.5g/l water @20ml/m2
  4. If thorough cleaning of containers is not possible, the containers may need to be sealed and fumigated with phosphine.

Controlling infestations within the grain

  • All storage should be checked, preferably every fortnight, and at least monthly.
  • Random samples need to taken from all grain and tested for infestation.
  • If there are more than 4 insects per kg some form of treatment is required.
  • A simple rule of thumb for the number of bags to be sampled is to use the square root of the lot size. For example if there are 100 bags in the lot, samples should be taken from 10 bags.

Grain treatments

  • Malathion is a widely used chemical and is toxic to insects if it comes into direct contact with the pest.
  • It is considered one of the safest organophosphate insecticides .
  • As a grain treatment Malathion is applied at the time grain is stored.
  •  Treated grain should not be sold for at least 7 days nor eaten within 60 days of treatment.

Fumigation

Fumigants are effective against storage pests because as gases they can reach the pests in the most remote hiding place. The range of safe fumigant chemicals that can be used is now restricted to phosphine and carbon dioxide.

Phosphine fumigation

  • Phosphine fumigation is undertaken using tablets and pellets. These tablets and pellets release phosphine gas when they come into contact with humid air.
  • Phosphine is toxic to all insects. When insects are exposed to fumigation in a sealed environment all stages of development from the eggs, larvae, pupae to adults are killed.
  • Care must be taken when using phosphine as a gas as it is very toxic to humans.
  • Fumigation must take place in an enclosure that can be tightly sealed. Once the exposure time is ended, the grain must be aerated and the bin checked for residual phosphine gas before entry.

Table 1: Minimum Exposure times at 60% Relative Humidity

Temperature (oC)

Tablets (days)

Pellets (days)

Under 5

No fumigation

No fumigation

5-10

10

8

11-15

5

4

16-25

4

3

Over 25

3

3

Example:  at 25oC, the minimum exposure time for tablets and/or pellets is 3 days

Carbon dioxide fumigation

  • With carbon dioxide fumigation, much of the oxygen in the storage bin is replaced by carbon dioxide that suffocates, dehydrates and also produces toxic chemicals in the blood of the insects. 
  • To be effective, elevated carbon dioxide levels must be maintained until all insects die.
  • The required exposure time depends on the percentage of carbon dioxide and the temperature of the grain. The cost of CO2 fumigation is high.

Table 2: Guidelines for Carbon Dioxide Application

Grain Temperature (oC)

Minimum CO2 Levels (%)

Days for control

25-30

80

8.5

25-30

60

11

25-30

40

17

25-30

20

Weeks to months

Physical conditions

Temperature

  • The ideal temperature for stored product insect growth is 25-30oC.
  • Aerating the grain immediately after harvest so the grain is cooled will significantly reduce insect infestation.
  • At 15oC the insects stop laying eggs and development stops. At lower temperatures insects will die.
  • High temperatures will also kill all stages of insects (eggs, pupae, larvae and adult) if exposed for a sufficient period of time.
  • Generally insects need to be exposed to temperatures of 50-55oC for at least 15 minutes.

Diatomaceous earth

Control of some insects (e.g. rusty grain beetle) can be achieved by using a non-toxic dust made from prehistoric diatoms. When the insect comes in contact with this dust, the waxy covering on the exoskeleton is absorbed, leaving them prone to dehydration and death. The product is applied as the grain is loaded into the bin and is most effective when applied to dry grain at harvest. Control can take up to 5-6 weeks.

Fungi in stored rice

Contamination of seed and grain with fungal organisms may result in poor germination, seedling vigor or grain quality. The most common storage fungi are species of Aspergillus and Penicillium. Contamination occurs through small quantities of spores contaminating the grain as it is going into storage from the harvest, in handling and storage equipment or from spores already in the storage structures. Under high temperatures and moisture this small amount of inoculum can increase rapidly. The development of fungi is influenced by the:

  • Moisture content of the stored grain
  • Temperature
  • Condition of the grain going into storage
  • Length of time the is grain stored and
  • Amount of insect and mite activity in the grain.

Fungi cause two distinct problems in storage grains. These are grain spoilage from fungal growth or molds and the production of poisonous mycotoxins. Grain spoilage causes poor germination, loss of weight, loss of nutritive value, poor milling quality and deterioration in flavor and color of the rice.

Management Options

Safe Storage Conditions

  • Grain damage by fungi will be reduced when grain and seed is:
  • Stored at moisture contents below 13-14%. It is important to be aware that there is variation in moisture content through a grain mass and fungi will grow where moisture is suitable and not according to the average moisture content of the grain stack
  • Stored at temperatures below 20oC and above 40ooC.
  • Not cracked and broken kernels or contain large amount of foreign material - broken or cracked kernels are more likely to be contaminated going into storage and more likely to be invaded once they are in storage than whole kernels.
  • Free from fungi coming into store. Grains moderately invaded by storage fungi develop damage at lower moisture content, at a lower temperature and in a shorter time period than grain free or almost free of storage fungi.
  • Stored for a shorter period. Grain that is to be stored for only a few weeks before processing can be stored safely with a higher moisture content and more extensive invasion by storage fungi and can be kept at a higher temperature than grain that is to be stored for months or years.
  • Free from insect and mites. Insects and mites can carry fungal spores on their bodies thus introducing storage fungi into the grain mass. Insect activity in a grain mass leads to an increase in both the temperature and moisture content of the grain surrounding the insect infestation. In these 'hot spots' conditions may be favorable for mold growth.

Grain treatment

  • Infected seeds can be treated by either physical or chemical treatments, or a combination of both methods.
  • Seed borne bacteria can be treated by dry heat at 65oC for 6 days or dipping in hot water treatment at 52-55oC.
  • Seeds can also be treatment with fungicides such as Dithane M-45 and Benlate at the rate of 3 grams kg-1.
  • The most effective method of treating mycotoxin problems is avoidance. This is possible by drying the grain to safe moisture content before storage, reducing physical damage to the grain during harvesting and storage and ensuring clean, dry insect-proof storage conditions.

Minimize Damage

Little can be done to prevent or reduce the invasion of crops in the field by fungi. However, the following recommendations should help prevent storage fungi problems or minimize damage from storage fungi in stored grains.

  1. Harvest as soon as the moisture content allows for minimum grain damage.
  2. Adjust the harvesting equipment for minimum kernel or seed damage and maximum cleaning.
  3. Clean all grain harvesting and handling equipment thoroughly before beginning to harvest. Clean bins or storage facilities thoroughly to remove dirt, dust and other foreign material, crop debris, chaff and grain debris.
  4. Clean grain going into storage to remove lightweight and broken kernels or seeds as well as foreign material and fines.
  5. Moisture content is by far the most important factor affecting the growth of fungi in stored grain. After harvest, grain should be dried to safe moisture contents as quickly as possible.
  6. Aerate grain to safe and equalized temperatures through the grain mass.
  7. Protect grain from insect and mite damage.
  8. Check stored grain on a regular basis and aerate as needed to maintain low moisture and proper temperature.

Rodents in storage

Rats have been estimated to damage more than 1% of the world cereal crops and, in developing countries, estimates of 3-5% have commonly been reported. There are around 50 diseases which can be transferred to humans by rodents, including typhoid, paratyphoid, and scabies. In addition, rodents may be vectors of a large number of diseases affecting domestic animals. As rodents prefer food rich in proteins and vitamins and feed mainly on the embryo, they cause particular damage to the nutritional value and germination ability of seeds.

The three most important rodent species are:

  • Black rat or House rat (Rattus rattus)
  • Norway rat or Common rat (Rattus norvegicus)
  • House mouse (Mus musculus)

There are also a number of species that are of great importance in specific regions:

  • Multi-mammate rat (Mastomys natalensis) in Africa and the Middle East;
  • Bandicoot rat (Bandicota bengalensis) in Southern and South East Asia;
  • Pacific rat (Rattus exulans) in South East Asia, also occurring in Southern Asia

1. Feeding on stored produce

Rats consume about 25 gm of food per day and mice eat approximately 3-4 gm per day.  Besides eating stored produce, rodents contaminate a lot of the stored produce with urine, feces, hair and pathogenic agents. As it is extremely difficult to remove contamination, infested batches often have to be declared unfit for human consumption.

2. Damage to material and equipment

(e.g. tarpaulins, bags, pallets, sprayers) and to the store itself (cables, doors).

These often lead to subsequent damage:

  • Produce leaking out of damaged bags or storage containers
  • Bag stacks collapsing due to damage to the lower layers
  • Short circuits leading to sparks or fire from cables being chewed
  • Silos and warehouses may subside or even collapse as a result of being undermined
  • Drainage canals around a store may be damaged.

Signs of rodent infestation

When there are signs of rodent infestation, it is necessary to conduct a thorough investigation of the store, its immediate surrounding area and neighboring land. There are a large number of clear signs of rodent infestation:

  1. Live animals: Rodents are mainly active at night. If animals are nonetheless seen during the daytime, this is a sign of an already advanced stage of infestation.
  2. Droppings: The shape, size and appearance of droppings can provide information as to the species of rodent and the degree of infestation. The droppings of Norway rats are around 20mm in length and are found along their runs. The droppings of Black rats are around 15mm long and are shaped like a banana. Mouse droppings are between 3 and 8mm in length and irregular in shape. Droppings are soft and shiny when fresh, becoming crumbly and matt black or gray in color after 2 - 3 days.
  3. Runs and tracks:  Runs, such as those of Norway rats, are to be found along the foot of walls, fences or across rubble. They virtually never cross open areas of land, but always pass through overgrown territory, often being concealed by long grass. Runs inside buildings can be recognized by the fact that they are free of dust. The animal's fur coming into contact with the wall leaves dark, greasy stains. Even Black rats, which do not have any fixed runs, can leave similar greasy stains at points which they pass regularly, e.g. when climbing over roof beams.
  4. Footprints and tail marks:  Rats and mice leave footprints and tail marks in the dust. If you suspect there might be rodent infestation, scatter some sort of powder (talcum powder or flour) on the door at several places in the store and later check for traces. The size of the back feet serves as an indication of the species of rodent:
  • Back feet larger than 30mm: Black rat, Norway rat, Bandicoot rat.
  • Back feet smaller than 30mm: House mouse, Multi-mammate rat, and Pacific rat.
  1. Tell-tale damage:  Rats leave relatively large fragments of grain they have nibbled at (gnaw marks). They generally only eat the embryo of maize. Sharp and small leftovers are typical for mice. Damaged sacks where grain is spilled and scattered can be a further sign of rodent attack. Small heaps of grain beneath bag stacks are a clear sign. These should be checked for using a torch on regular controls. Attention should be paid to damaged doors, cables and other material.
  2. Burrows and nests: Depending on their habits, rodents either build nests inside the store in corners as well as in the roof area or in burrows outside the store. Rat holes have a diameter of between 6 and 8cm, whereas mice holes are around 2cm in diameter. These holes can be found particularly in overgrown areas or close to the foundations of a store.
  3. Urine: Urine traces are fluorescent in ultraviolet light. Where available, ultraviolet lamps can be used to look for traces of urine.

Preventive measures

The most essential factors for the occurrence of rodents are:

  • Sufficient supplies of food
  • Protected places in which to build burrows and nests
  • Hiding places
  • Access to produce

Good store management and preventive measures taken as part of an integrated control program can help to deal with these factors.

Storage Hygiene and Technical Measures

  • Keep the store absolutely clean! Remove any spilt grain immediately as it attracts rodents!
  • Store bags in tidy stacks set up on pallets, ensuring that there is a space of Im all round the stack!
  • Store any empty or old bags and fumigation sheets on pallets, and if possible in separate stores!
  • Keep the store free of rubbish in order not to provide the animals with any places to hide or nest! Bum or bury it!
  • Keeps the area surrounding the store free of tall weeds so as not to give the animals any cover! They have an aversion to crossing open spaces.
  • Keep the area in the vicinity of the store free of any stagnant water and ensure that rainwater is drained away, as it can be used as source of drinking water.

Sourc: IRRI

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