Unit 11-DDP- DR. SUSHIL NEUPANE.pdf

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PREPARED BY DR. SUSHIL NEUPANE (B.V.SC. AND A.H., IAAS, TU)
Unit 11: Knowing eggs and its nutritive aspects
11.1. Process of egg formation, nutritive value of egg
11.2. Collection, handling, and storage of egg
11.3. Preservation techniques of egg
Formation of the egg
The egg is formed gradually over a period of about 25 hours. Many organs and systems help
to convert raw materials from the food eaten by the hen into the various substances that
become part of the egg.
The ovary
The hen, unlike most animals, has only one functional ovary - the left one - situated in the
body cavity near the backbone. At the time of hatching, the female chick has up to 4000 tiny
ova (reproductive cells), from some of which full-sized yolks may develop when the hen
matures. Each yolk (ovum) is enclosed in a thin-walled sac, or follicle, attached to the ovary.
This sac is richly supplied with blood.
The oviduct
The mature yolk is released when the sac ruptures, and is received by the funnel of the left
oviduct (the right oviduct is not functional). The left oviduct is a coiled or folded tube about
80 cm in length.

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Proportion of the different egg compartments in the hen’s egg
Proportion of the different egg compartments in domestic bird species
The nutritive value of the egg
The egg is one of the most complete and versatile foods available. It consists of
approximately 10% shell, 58% white and 32% yolk. Neither the colour of the shell nor that
of the yolk affects the egg’s nutritive value. The average egg provides approximately 313
kilojoules of energy, of which 80% comes from the yolk.
The nutritive content of an average large egg (containing 50 g of edible egg) includes:
6.3 g protein
0.6 g carbohydrates
5.0 g fat (this includes 0.21 g cholesterol).
Egg protein is of high quality and is easily digestible. Almost all of the fat in the egg is found
in the yolk and is easily digested.

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Vitamins: Eggs contain every vitamin except vitamin C. They are particularly high in
vitamins A, D, and B12, and also contain B1 and riboflavin. Provided that laying hens are
supplemented according to the Optimum Vitamin Nutrition concept (see chapter ‘Optimum
vitamin nutrition of laying hens’), eggs are an important vehicle to complement the essential
vitamin supply to the human population.
Minerals: Eggs are a good source of iron and phosphorus and also supply calcium, copper,
iodine, magnesium, manganese, potassium, sodium, zinc, chloride and sulphur. All these
minerals are present as organic chelates, highly bioavailable, in the edible part of the egg.
Collection, handling, storage and transport of eggs
Eggs should be collected, handled, stored and transported in a manner that minimizes
contamination and/or damage to the egg or egg shell, and with appropriate attention to time-
temperature considerations, particularly temperature fluctuations.
Appropriate measures should be implemented during disposal of unsafe and unsuitable
eggs to protect other eggs from contamination.
Proper collection, whether using manual or automated methods, handling, storage and
transport of eggs are important elements of the system of controls necessary to produce safe
and suitable eggs and egg products. Contact with unsanitary equipment and foreign materials
or methods that cause damage to the shell, may contribute to egg contamination.
Whether manual or automated methods are used to collect eggs, producers should minimize
the time between egg laying and further handling or processing. In particular, the time
between egg laying and controlled temperature storage should be minimized.
Methods used to collect, handle, store and transport eggs should minimize damage to
the shell, and avoid contamination and practices should reflect the following points:
 Cracked and/or dirty eggs should be excluded from the table egg trade.
 Cracked and/or dirty eggs should be directed to a processing or packing
establishment, as appropriate, as soon as possible after collection
 Hygienic practices, which take into account time and temperature factors, should be
used to protect the egg from surface moisture in order to minimize microbial growth.
 Where appropriate, broken and/or dirty eggs should be segregated from clean and
intact eggs.

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 Broken eggs and incubator eggs should not be used for human consumption and be
disposed of in a safe manner.
 Egg processors should communicate any specific requirements at farm level (i.e.
time/temperature controls) to the egg producer
Egg collection equipment
Collection equipment should be made of materials that are non-toxic and be designed,
constructed, installed, maintained and used in a manner to facilitate good hygiene practices.
It is important to prevent any damage to the eggshells by collecting equipment since such
damage can lead to contamination and consequently adversely affects the safety and
suitability of eggs and egg products. It is also important that the equipment is maintained to
a standard of cleanliness adequate to prevent contamination of the eggs.
 Where used, egg collecting equipment and containers should be cleaned and
disinfected regularly, or if necessary replaced, and with sufficient frequency to
minimize or prevent contamination of eggs.
 Single use containers should not be reused.
 Egg collecting equipment should be maintained in proper working condition and this
should be periodically verified.
STORAGE OF EGGS
The storage of shell eggs during the main laying season, in order to conserve them for
consumption when they are scarce, has been practiced for many centuries.
For the successful storage of eggs, the following conditions must be met.
 The eggs placed in storage must be clean; they must not be washed or wet.
 Packaging material used should be new, clean and odorless.
 Loss of water due to evaporation should be reduced to a minimum.
 The storage room must be free from tainting products and materials and should be
cleaned regularly with odorless detergent sanitizers.
 The storage room must be kept at a constant temperature and humidity must be
checked.
 There should be air circulation in the storage room.
 Eggs should be stored so that they are allowed to breathe.

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 As far as possible, interior quality should be monitored; there should be a good
proportion of thick white, the yolk should stand up well, and the flavour of white and
yolk should be good.
Cold storage of eggs
In the tropics, eggs can deteriorate very quickly unless they are stored at low temperatures.
The ideal temperature for storage in such climates is 13°C or lower (usually between 10°
and 13° C). Here refrigeration is a necessity for successful commercial storage; however, it
may be unavailable or the costs too high.
The most important factors in successful cold storage are as follows.
 The selection and packaging of eggs.
 The equipment and preparation of the cold store.
 Proper temperature, humidity and air circulation.
 Periodic testing for quality.
 The gradual adjustment of eggs to higher temperatures when removed from storage.
The selection and packaging of eggs for storage. Eggs for storage must be clean, of good
interior quality and have a sound shell. The period of time between laying and storage should
not be more than a few days. The eggs should be kept cool during that time.
Packaging materials used for storage should be new, clean, odorless and free from damage.
When packaging material is reused, it is extremely important that it is clean, odorless and
free from damage. It is important that the material used allow the eggs to "breathe" and to
be free from tainting odors.
The equipment and preparation of the cold store. The storage room should have a
concrete floor that is washable. Walls and ceilings must also be washable. Wooden buildings
have been found to be satisfactory, provided they do not impart foreign odors or flavors to
the eggs. The room should be scrubbed thoroughly with hot water and soap or an odorless
detergent sanitizer before being used. A final rinse with a hypochlorite solution will help
greatly in deodorizing the storeroom. A liberal application of freshly slaked lime to
unpainted plaster surfaces will also help. The storage room should be aired and dried out
thoroughly after cleaning, then closed up and the refrigeration turned on. It is best to allow
several days for the temperature and humidity to stabilize before introducing the eggs.

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Proper temperature, humidity and air circulation. Careful and accurate control of the air
condition is essential. A temperature between - 1.5° and - 0° C is recommended. At a
temperature of - 2.5° C eggs freeze. The room should be well constructed and insulated and
the refrigeration should be capable of maintaining an adequate uniform temperature in all
areas. The cases of eggs should be separated by wood-strips and kept well away from the
walls so as not to obstruct air circulation. Periodic ventilation of the storage room is advisable
to promote air exchange.
The relative humidity should be between 80 and 85 percent at a cold storage temperature of
- 1° C. At cold storage temperatures of about 10° C the relative humidity should be between
75 and 80 percent. In such instances, on average, egg weight loss should not exceed 0.5
percent per month. During the early stages of storage when the packaging material is
absorbing moisture at a high rate, the floors should be sprinkled with clean water several
times a day. If forced-air circulation is feasible, a controlled temperature water-spray air
washer may be used. If the humidity becomes excessive, part of the air can be cycled through
a unit containing calcium chloride. Where eggs have been oiled less attention can be paid to
the humidity level.
Periodic testing for quality. Periodic quality checks are essential if the risk of heavy egg
losses is to be avoided. Every month or so a sample of eggs should be selected from the
various lots and tested. Usually a sample of about 1 percent of all eggs in storage may be
sufficient. For example, if 3000 eggs are kept in storage, 30 eggs sampled from various egg
cases will enable a good estimation of the general quality level of the eggs. If there is
evidence of excessive deterioration, it is best to dispose of the eggs quickly, after eliminating
those that are unfit for consumption.
PRESERVATION OF EGGS
In order to preserve eggs only good quality eggs should be produced. Therefore any method
of preservation starts from the point of production itself.
The following practices are recommended as routine for the production of quality eggs on
the farm.
 Collection of eggs at least 3 times daily.

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 Using a clean receptacle with ventilated sides and bottom, preferably filler flats.
 Careful handling of eggs during collection and while keeping in filler flats etc.,
 Cooling the eggs quickly to 50°F or less at 75-85% relative humidity.
 Marketing the eggs at least twice weekly.
Preservation
The shell of an egg normally carries a wide range of microorganisms on its surface which
are mostly responsible for spoilage of eggs.Many methods have been used in the past to
counteract this and extend the shelf life of eggs. These include:
Dry packing
Eggs are kept in an earthen pot with clean dry packing material and the pot is buried in wet
sand.
Immersion in liquids
This is fairly an old method and it primarily prevents the evaporation of moisture from the
egg. Depending on the liquid used it may also inhibit bacterial decomposition by chemicals
action or by physical means such as occlusion of air passages/pores.
Lime water treatment
Lime water is prepared by mixing about 0.5kg of quick lime (calcium oxide) in about 1 litre
of boiling water. The mixture is left to settle overnight and the clean supernatant liquid is
poured out into a jar. Sodium chloride of 112 grams per litre may also be added to increase
the specific gravity of water and will minimize the chance of breakage of eggs.
 In this solution, 2.5 liters of cold water is added and filtered through muslin cloth.
 Keep the eggs to be preserved in a glass jar or earthen pot and pour the lime solution
over the eggs till all the eggs are completely immersed.
 Eggs have to be kept in this solution for 24 hours to get maximum beneficial effect.
 After 24 hours they are taken out, dried and arranged in filler flats.
 Eggs can be kept for 2-3 months in a good edible condition at normal ambient
temperature.
The only disadvantage however, is the taste of lime can be detected in the eggs.

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Water glass method
 A 10% solution of sodium silicate is prepared in hot water and allowed to cool.
 The cooled solution is poured into a jar containing the eggs till they are immersed
completely.
 The jar is covered and kept in a cool place where the temperature should not exceed
above 70°F.
 Eggs preserved by this method are usually punctured before boiling to avoid the
breakage of shell while boiling and it also helps for easy peeling of shell.
Shell - Sealing treatments
When the shell is sealed through this treatment the water vapour and CO2 do not escape and
microorganisms are unable to penetrate the shell.
Coating with oil
 The rate of CO2 escape is considerably reduced.
 This is a fairly successful method of rendering the egg less permeable.
 It can be done by simply dipping the egg in a bowl of tasteless, odorless, colourless
edible oil, having a specific gravity of about 0.855 to 0.870 at 15°C; viscosity should
not be more than 70 to 90 and having a high boiling point so that at lower temperature
it remains in the liquid form.
 The eggs are immersed only for a moment and are then removed and the excess oil
is allowed to drain.
 If oil treatment is to be effective it should be done preferably at the point of
production the day after the egg is laid.
 Oiling is not a substitute for refrigeration.
 These eggs must be held at a low temperature.
 Cotton seed, linseed and groundnut oil are good sealing agents but mineral oils are
preferable since they are less subject to oxidative changes during storage. oil
immersed eggs and these eggs are not likely to absorb foreign odours.
 The oil treatment can also be done by spraying using a hand or electric sprayer.
 Eggs can be sealed under vacuum.
 Oil may be successfully used in vacuum impregnation method.

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 The egg is first immersed in oil and then subjected to reduced atmospheric pressure,
when normal pressure is restored the tendency of the air to enter the pores of the shell
causes the solution also to be drawn in.
 The oil does not penetrate through the egg membranes.
The commercial egg treatment with oils are
 Heavy paraffin oil (Central Food Technology Research Institute
 Myvacet 9-40 (developed at CFTRI - Mysore)
 Myvacet 5
 Myvacet 7
 Petroleum jelly
 Liquid paraffin
 Paraffin wax
 Coconut oil
 Dalda
 Carboxyl methyl cellulose
 Technical white oil.
Thermostabilization
 This method is good for fertile eggs since it kills the embryos and therefore is also
known as 'defertilization' method.
 It essentially consists of immersing shell eggs in hot water at 130oF for 30 minutes
which tend to coagulate the albumin and then the egg is cooled under tap water.
 Treated eggs remain edible for 3 to 4 weeks even during summer months.
 Though this method has many advantages such as stabilizing of the albumin and
sterilization of the egg shell, the egg loses the property of foaming to a remarkable
extent.
 Moreover, embryonic development in fertile eggs is completely arrested.
Over-wrapping
 For over wrapping of eggs polyethylene, cellophane, polyvinylidene and other
transparent, thin but sufficiently strong, films are used.
 These films should be impervious to gases and moisture.
 Over wrapping of eggs in different atmosphere like carbon dioxide, vacuum etc. have
been tried.

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Cold storage
 This is the best and most efficient method for commercial storage.
 Eggs for cold storage must be clean, unbroken, and free from fungus and other
infections.
 A temperature of 0°C or 30-32°F and relative humidity of 85-90% is recommended
for cold storage of eggs to preserve them for 5 to 8 months.
 For short period of preservation of 2 to 3 months, eggs can be stored at 10-12°C or
50-55°F with a relative humidity of 60-70%.
 Intact eggs are held at the lowest possible temperature that will avoid freezing and
bursting of the shells.
 It has been observed that intact eggs do not freeze at temperature between -1.5°C and
-2°C and the relative humidity must not go beyond 90%.
Dried and frozen eggs
 This is another method of preserving egg contents or edible eggs.
 Egg products of commercial utility are prepared by drying or freezing eggs.
 Albumin flakes, yolk and egg white powder can be produced by drying process.
 Frozen yolk or frozen egg white can be produced by freezing.
 For egg white powder production the best known method is spray drying and for
albumin flakes, pan or cabinet drying method is mostly adopted.

Unit 11-DDP- DR. SUSHIL NEUPANE.pdf

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Unit 11-DDP- DR. SUSHIL NEUPANE.pdf