Preservation and Maintenance of Eggs
A freshly laid egg can be assumed to have a highest quality. Since egg is full of essential nutrients, deteriorative changes soon start taking place which may pose a danger to the excellent sensory attributes of this nourishing and satisfying food item. Cleanliness and soundness of shell is the first step to assure the quality of egg to the consumers. The shell quality deficiencies mostly relate to the production practices adopted at the farm. Proper handling of eggs can delay the decline in the quality. Following precautions should be taken during handling of eggs:
- Eggs should be collected 3 to 4 times per day. This will result in less dirty eggs and fewer breakages.
- After collection, eggs should be shifted to holding room maintained at a temperature of about 15Â°C and 70 to 80% RH atleast for 12 hours.
- Eggs should be properly packed in filler flats with broad end up. Bulk packing should be done in fibre board cartons.
- Eggs should be rapidly moved through the marketing channel so as to reduce the period between production and consumption.
All preservation methods for shell eggs have been designed to retard one or more of the following physico-chemical alterations which lower the quality of egg as it ages:
- As the surface of egg dries, the keratin cuticle shrinks and size of shell pores increases rendering it easier for gases and micro-organisms to pass in and out of the shell.
- As the warm egg cools down, the egg contents also contract, resulting in the formation of air cell.
- The breakdown of carbonic acid causing loss of carbon dioxide from the albumen is rapid during the first few hours after an egg is laid. The alkaline pH acts on the mucin fibres to disturb the thick gel of albumen making it thin or watery.
- As the egg ages, water migrates from the albumen to the yolk which may overstretch, weaken or even rupture the vitelline membrane.
Following preservation methods are employed to maintain the quality of shell eggs:
Earlier, it was a general practice to dry-clean dirty egg shells by abrasive mounting on a mechanical wheel. This practice has now become obsolete because it weakens the shell. These days washing in warm water containing a detergent sanitizer is an effective way of cleaning the eggs with dirty shells. A temperature difference of 10-15Â°C between eggs and wash water is ideal, otherwise there may be problem of crack shells. Besides, eggs should not be immersed in warm water for more than 3-4 minutes. After washing, the eggs should be dried promptly. Wash water should be changed after washing every five to six baskets of eggs. It should be emphasised that only dirty eggs are subjected to washing. It not only reduces the microbial load on the egg shell surface but also improves the appearance and consumer appeal.
Oil coating spray of eggs has become very popular for short term storage of this commodity. Coating oil forms a thin film on the surface of the shell sealing the pores. It should be done as early as possible, preferably within first few hours after laying of eggs because loss of CO2 is more during this period and evaporation of moisture is also more during the first few days. Egg coating oil should be colourless, odourless and conform to food grade. Coating is done by dipping the eggs in the groundnut oil whereas for oil spray, the eggs are arranged in the filler flats with their broad end up. If the eggs need washing, oil coating should be done after washing. It is important to drain out excess oil before packaging. The temperature of oil should be in range of 15 to 30Â°C for ideal results. Oil treatment safeguards the quality of albumen for atleast 7 days because it effectively seals the shell pores.
This method of preservation is suitable for long term storage of clean eggs in the main laying season and abundant availability. The temperature of cold store is maintained at 0Â°C (32Â°F) and relative humidity between 80 to 85 per cent. An anteroom with intermediate temperature is generally provided to check condensation of water vapour on the eggs during removal. Use of new egg packing trays are advised for cold storage. Like all other animal products, eggs also pick up strong odour, so the same cold store cannot be used for storing onion, garlic or any other commodity with strong odour. The quality of shell eggs can be maintained for about 6 months in a cold storage. Oil coating of eggs prior to cold storage can further enhance their keeping quality. Such eggs could keep well at 14oC and 90% RH for a period ot 8 months.
This preservation method involves stabilisation of albumen quality by holding the eggs in an oil bath maintained at 55Â°C for 15 minutes or 58oC for 10 minutes. This process brings about coagulation of thin albumen just below the shell membranes, thereby blocking the passage of air and moisture. In addition, oil coating of shell pores also takes place. Thus keeping quality of eggs is maintained for sometimes and thinning of egg white is retarded. Alternatively, eggs are immersed in hot water at 71Â°C for 2 to 3 seconds. In this flash heat treatment, bacteria present on the surface of the shell are destroyed and a thin film of albumen just below the shell membrane is coagulated sealing the egg shell from inside.
IMMERSION IN LIQUIDS
Under rural conditions, lime-water or water-glass immersion are most useful. In lime-water treatment, a litre of boiling water is added to 1 kg of quick lime and allowed to cool. Now 5 litres of water and 250 g of table salt are added to it. The solution is strained through a fine cloth when the mixture settles down. Eggs are dipped in the clear fluid overnight and then dried at room temperature. In this process, an additional thin film of calcium carbonate is deposited on the egg shell and seals the pores. Such eggs can be stored for a month at ambient temperature. In water-glass treatment, one part of sodium silicate is mixed in 10 parts of water and eggs are dipped overnight. In this process, a thin precipitate of silica is deposited on the egg shell and partially seals the pores.
It is clear from the above discussion that eggs should be collected frequently, held initially at low temperature and then a suitable preservation method be employed to maintain its keeping quality for anticipated consumer acceptance.