Egg processing is a huge segment of food processing industry where eggs are processed into various convenient form, for consumption. Eggs are most common reproductive form of different species but their high nutritive value in terms of protein, carbohydrate, lipids, and other minerals has always made it suitable for human consumption.
Processing of eggs vary with the intended use. Egg processing includes processing of whole egg, or separate processing of albumin (egg white), yolk (yellow part). Also type of processing involves freezing, dehydration, spray drying to powder etc. Egg products can be classified into refrigerated liquid product, frozen product, dried and dehydrated product, or speciality product such as pre-cooked products such as egg patties, egg pizza, freeze dried scrambled eggs etc. But with all the nutritive values, come risk contamination, and high susceptibility to microbial spoilage.
- Structure of Egg
An egg structurally composed of-
- Shell: It is hard outer layer of egg with function of protection to outer environmental stress and harmful contamination.
- Shell membrane: There are two shell membrane, outer and inner, which are fibres and porous in nature. They provide extra strength to outer eggshell
- Albumin: Also known as the egg white is rich source of protein and an indicating parameter for quality of egg. In good grade of eggs, when broken, two distinguish layer of thin and thick albumin is there with thick albumin layer spreading less, while in low grade eggs, both thin and thick layer of albumin are indistinguishable.
- Chalaza- It is a cord like structure that helps keeping the yolk at centre of the egg.
- Vitelline (Yolk)- Also known as Egg yellow, is major source of fat and vitamins of egg.
- Air Cell- They are found in the larger end of egg, which is formed due to the cooling of egg after it is laid. It increases in size with the age hence, smaller air pocket indicates freshness of eggs.
- Functional Properties
Coagulation, emulsification, and foam formation are key functional attribute of eggs that makes it highly desirable as a food ingredient.
- Coagulation- Coagulating property of egg helps it to eb used as thickening agents. Eggs are good source of protein and when subjected to heat, protein coagulate forming a network. Coagulation time of both egg white (62-65 Deg. C.) and yellow (65-70 Deg. C.) differs as both differ in the protein content.
- Emulsification- Few protein and phospholipids content in eggs provides it a emulsifying property.
- Foam Formation- Foaming in egg is evident, when it is whisked at high intensity. When whisked/beaten, it entraps the air and generates foam like functional characteristics.
- Processing of Egg
Egg processing involves following steps in general-
- Receiving Shelled Eggs-
Receiving of eggs can be either
- In-line process- Where eggs are received directly from farm and farm is near egg processing facility.
- Off-line process- Eggs are received from contractors, and receiving time is more compared to in-line receiving process. Eggs reaching the egg processing factory are packed, palletize, and transported.
- Washing and Sanitizing- Eggs received in egg processing factory from farm are dirty with dust from farm, feathers and birds dropping on the egg. Washing process includes jet water spray to remove loose dirt and rotating brush to clean off hard to remove dirt.
- Quality Check- Candling is one of the most used quality checking mechanism where the eggs are rotated over several time over bright light to check eth internal quality of egg. Depending upon quality check they are categorized into different grade class and processed separately. All the dirty, leaker and damaged eggs are removed from the processing conveyor.
- Egg Breaking- All the acceptable quality eggs, free from any sort of Internal and external defects are moved forward for egg breaking process. In this process, eggs are sucked up via vacuum and are broken into two halves to get the internal egg liquid. Liquid moves forward for processing while eggshell is taken to the shell collection area for being disposed/or transported to farm, where it is used as animal feed.
- Separation- Extracted egg liquid go under separation process where it is subjected to liquid white and yolk separation. The separated liquids are cooled down and transferred to respective storage tanks.
- Pasteurization- Eggs high nutritive value attracts microbial contamination and hence to prevent microbial growth, they are subjected to high temperature treatment and then rapidly cooling it to low temperature. After pasteurization they are, either directly packed, or processed further as per the requirement like freezing, drying for powder formation.
- Storage- Storage condition is preferred to be as low temperature as possible. Egg products can have shelf life up to 3-4 months if kept at -1-2 Deg. C. Liquid eggs before pasteurization is also kept at temperature of below 4 Deg. C so maintain the quality of the product.
There are high opportunities in egg processing industries to improve food safety as there is still a significant risk to consumers, microbiological, specifically Salmonella sp.