Eggs are an important nutrient in the diet of people of all ages. The food prepared using eggs attract consumers due to properties imparted by the constituents in eggs. The properties of the eggs are used in imparting characteristics to cakes among Western food, and to Watalappan among Sri Lankan food. The import of eggs due to the failure of the poultry industry to meet the demand in the country has led to a public discussion and concern on the safety of imported eggs as a food.
Nutritional quality and production
An egg is a safe, healthy food. The consumption of up to three eggs per day is considered healthy scientifically. Eggs consist of the yolk (yellow), albumen (white) and the shell, in addition to membranes in between them. They are characterised by the high protein content, and a variety of vitamins. The nutritional quality of eggs is further improved by introducing omega-three-fatty acids and iodine through the feed of the hens in Japan.
The quality of eggs depends on the feed provided to hens and the way in which the birds are maintained in the poultry industry. The safety of eggs as a food depends on conditions during the growth of the egg inside the hen and the environmental conditions. The climate, the feed, clean water, the cleanliness of the surroundings, the exposure of the hens to sunlight, and breathing fresh air contributes to the healthy composition of eggs. However, the way that the eggs are handled from the farm to the table may render the eggs unsuitable for consumption.
An egg contains about six grams of proteins and six grams of fats, on average. The hens should be provided with a meal containing 16–18 % protein, 3.5% calcium along with carbohydrates, vitamins and minerals in adequate quantities. As an egg contains about 50% water, the hens should be provided with clean water continuously. An egg contains other nutrients including phosphorus, zinc, vitamins A, B6, B12, D, folic acid and thiamine. An imbalance among these constituents affects the nutritional quality and properties that contribute value to the egg as an ingredient in preparing food.
Poultry farmers are aware that the composition of an egg could be changed with the types of feed and chemicals added to the feed. They add various permitted chemicals to the feed in order to achieve a better appearance and to improve the longevity-related qualities of eggs. Baking soda and ammonium chloride are used to improve the properties of the eggshell. Potassium chloride is used to make the hens thirsty so that they would consume more water. In some countries, antibiotics are added to chicken feed. It is not an acceptable practice.
Eggs produced by hens living in the natural environment, feeding on natural ingredients such as insects, grains and earthworms are preferred by consumers as the yolk is an intense yellow. In commercial egg production, hens are maintained in limited spaces at a low cost, aiming at better profits. Under commercial conditions, scientifically designed feed, a controlled supply of water and exposure of hens to artificial light throughout the day and night are done, aimed at increased egg yields.
Food safety and quality of eggs
There are instances where the eggs lose value as a food, due to food safety issues. Poultry farmers, the industries using eggs as an ingredient in their recipes, and the consumers need to be aware of these undesirable situations. Deviations from the guidelines stipulated for the production, transport and storage of eggs, make eggs unsafe as a food. The major problems affecting the quality and safety of eggs occur due to the entry of disease causing microorganisms and unpermitted chemicals into eggs. The lack of basic nutrients in the chicken feed and the diseases occurring in hens, threaten the safety of eggs and deteriorate egg quality.
A thick egg white, a wholesome yolk and a thick shell are characteristics of good eggs. Thin, discoloured eggshells indicate the poor health of the hens. The egg white in poor quality eggs tends to flow easily, and the yolk tends to be discoloured. The shells of poor quality eggs may give a powdery appearance on the surface. The eggshell produced by hens living in warm climates tends to be thin. The eggshell, made of calcium carbonate, contains fine pores to allow respiration. Bacteria and viruses may contaminate the albumen and yolk of the eggs through these pores at times.
In warm environments, the hens consume less feed. Low feed consumption causes the reduction of the calcium intake, and imbalances in the ratio of phosphorus to calcium, resulting in weak eggshells. The imbalance also reduces the zinc to magnesium ratio in the yolk, thus reducing their nutritional value. When the hens live in cages, they produce more fat due to inadequate exercise, resulting in increased fat in eggs, thus reducing their nutritional quality. The chlorine in tap water reduces the protective effects of the eggshell. Similarly, the composition of the chicken feed influences the quality of the eggs. Feeding hens on cheap diets instead of scientifically designed feed, results in poor quality eggs.
Adding antibiotics and growth hormones into the feed provides the avenues for the entry of bacteria resistant to antibiotics, into the human body. Antibiotic resistant bacteria are harmful to human health as they cannot be controlled by common drugs. At times, the antibiotics and the growth hormones tend to survive boiling and other cooking methods applied to eggs. Natural ingredients such as chillies and ginger are reported to increase the hunger of the chicken.
The eggs get exposed to undesirable conditions during transport from the farm to the consumer. About 5% of the shells crack during transport and handling. The oozing of the yolk and the albumen of the damaged eggs, provides the opportunity for pathogenic bacteria to grow on other eggshells contaminated by the yolk and albumen. The damaged or weak eggshells allow easy entry of bacteria into the eggs. To reduce the access of bacteria on eggshells, there are guidelines for the dry cleaning of eggshells, and maintaining the temperature and relative humidity during storage and the transport of eggs. The eggs should be maintained at a temperature of 5-7 oCelsius and a relative humidity of 70-75% during transport and storage. The life processes in the eggs causing biochemical reactions tend to continue during storage, thus reducing the egg quality. Eggs could be kept safely and hygienically in a refrigerator for three weeks, and for a week after boiling and storing with the shell. In marketing eggs in developed countries, information on the egg producer is expected to be on the labels. The information on the labels help to trace the origins of the problems arising due to chemical and microbiological contaminants in eggs, and to apply corrective action in the future. There are specifications and guidelines by the Codex Alimentarius (Food Code) system, which are to be maintained in poultry farms. Importers insist on the maintenance of these conditions in farms and when handling eggs. It is the responsibility of the importers and the importing Governments to check on the application of Codex guidelines and to avoid the import of unsafe eggs.
The eggs are viewed against light in order to assess the characteristics of the yolk, the albumen and the air in recognising the quality. In the United States of America, eggs are classified as AA, A, and B based on the internal characteristics of eggs. The eggs are graded by weight as small (28-36 grams), medium (37- 44 grams), large (45-54 grams) and extra large (55-65 grams) in commerce.
The disease causing bacteria Salmonella exists on the outer shell of eggs, generally on 50% of the occasions. The presence of Salmonella inside the eggs is rare, though not impossible. It is essential to prevent the entry of Salmonella into food through eggs. The presence of faecal matter or bloodstains on the shell of eggs is an indication of the probable presence of Salmonella and other bacteria causing health problems. Selling such eggs is illegal. The eggs laid by sick hens may cause diseases in humans. It is illegal to use eggs from bird flu prevalent regions of countries. There are regions in countries around Sri Lanka with the prevalence of bird flu. Importing eggs from such areas may severely affect the poultry industry and the consumers in Sri Lanka.
India is a major producer with an annual production of 47 billion eggs. However, some of the reports on egg production in India do not attract consumers. Reports describe the hens sitting on their own faecal matter, ill fed hens, cobwebs in the cages, the presence of lice and insects, cannibalism, the consumption of cardboard and the consumption of feed containing antibiotics and pesticide residues in some instances. These setbacks affect the quality and safety of eggs. The lack of sanitation in poultry farms and the absence of quality control measures, allow for the contamination of eggs by pathogenic bacteria. Eggs produced in some areas of India have failed to attract the export market due to these poor practices.
Most reports on toxic metals in eggs do not indicate unsafe levels of toxic metals in eggs. Though the amounts of toxic metals in eggshells are higher than in the internal content, they remain within permitted levels for food. Past literature shows instances where toxic metals such as cadmium and lead, and unpermitted pesticide residues of Dichlorodiphenyltrichloroethane and Hexachlorocyclohexane in eggs from India. The presence of pesticide residues in eggs is reported from Jordan and Kenya too. The use of these pesticides, whose residues appeared in eggs, are not permitted for use in Sri Lanka. It is unacceptable to use chicken feed containing pesticide residues contravening international quality standards.
There is a fear among Sri Lankans of the possible spread of the bird flu virus through eggs. The virus gets inactivated on boiling or cooking the eggs. There are no reports anywhere indicating the transfer of bird flu through cooked eggs in the diet to humans. However, the globally accepted preventive measures on bird flu, recommend avoiding the purchase of eggs from farms in the radius of 10 kilometres from a place where bird flu was reported, and the prevention should be effective for 30 days from the day of the report. There were reports of bird flu virus from several locations in South India. There was a report on bird flu virus in the same area on 12 March,2023. There was a report on 15 March 2023, indicating that large numbers of poultry were destroyed so as to control the bird flu spread. It is the responsibility of the regulatory authorities in Sri Lanka to prevent the exposure of the consumers and the industry to hazardous situations that may arise through the import of eggs from regions already reported to be affected.
The safety of a food due to chemicals and disease causing microorganisms is decided by a scientific method in order to minimise the risk to humans. From this aspect, it is important to find the extent to which the principles of the “Hazard Analysis and Critical Control Points” concept is applied in the manufacture of chicken feed and egg production in the farms, and during storage and transport, before the import of eggs. In developed countries, strict regulatory measures are implemented at the entry points in seaports and airports, in order to prevent the entry of unhealthy food or diseases to the countries. Suspicious products are rejected. There are instances where the authorities in Sri Lanka prevented the entry of meat carrying microorganisms foreign to Sri Lanka, in order to safeguard the country from undesirable microorganisms. It is known that the heat processing of eggs destroys the bacteria and viruses on the outer surface of the eggs. It is also not a secret that the Sri Lankans on pilgrimage fall sick with upset stomachs when in neighbouring countries, due to the exposure to microorganisms unfamiliar to their bodies. Preventing the entry of pathogenic bacteria and disease causing viruses foreign to Sri Lanka is a national protective need.
(The writer is an Emeritus Professor in Food Science and Technology from the University of Peradeniya. He can be contacted at smrjee@gmail.com.)