LPT 321: Meat Science (1+1)

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.
  • 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^oF 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 minimise 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.
• 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^oF.
• 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^oC; 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.
  • 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
    1. Heavy paraffin oil (Central Food Technology Research Institute
    2. Myvacet 9-40 (developed at CFTRI - Mysore)
    3. Myvacet 5
    4. Myvacet 7
    5. Petroleum jelly
    6. Liquid paraffin
    7. Paraffin wax
    8. Coconut oil
    9. Dalda
    10. Carboxyl methyl cellulose
    11. 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 130^oF 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 looses 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.

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^oC or 30-32^oF 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^oC or 50-55^oF 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^oC and -2^oC 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.