ReviewEgg quality and safety with an overview of edible coating application for egg preservation
Introduction
The United States is the world’s third-largest producer of table eggs and the production of table eggs in the United States has remained dynamic during the past decade compared to Europe or China (Food and Agriculture Organization of the United Nations – FAO, 2013). According to United States Department of Agriculture (USDA), estimated egg consumption in the United States was 278.8 eggs per capita in 2018 and it was predicted to reach 279.8 eggs per capita in 2019 (USDA, 2019). Over the past two decades, the production and consumption of table eggs have increased all over the world. The FAO predicts production of 89 million tons of eggs in 2030 (Magdelaine, Braine, Gonnier, & Spiess, 2010).
The popularity of egg is rooted from its nutritional value. The water content of a hen’s egg is almost 74.4%, while the content of proteins and lipids are 12.3% and 11.6%, respectively (Tahergorabi & Jaczynski, 2016). The hen’s egg is also a rich dietary source of easily digestible fats. The easily digestible fats that are isolated from the hen’s egg include choline, unsaturated fats, cholesterol and cephalin-rich phospholipids. Such lipids are essential for ensuring the structural integrity of the cell membrane. Moreover, the digestible fats found in hens’ eggs are essential for the development of the nerve cells. Hens’ eggs are usually considered to be a low energy source of proteins. Approximately 148 kcal are obtained from 100 g of the hen’s egg (Mann, Maček, & Olsen, 2006). The protein quality of eggs is considered as standard for evaluating other foods since it is high (91%) if cooked. Hens’ eggs are also a rich dietary source of lysine and sulfur-containing amino acids. Hence, hens’ eggs provide essential amino acids for human consumption (Sparks, 2006). Apart from proteins and lipids, hens’ eggs are also rich dietary sources of different vitamins including A, D, E, and K and water-soluble B vitamins. It also contains minerals such as iron, calcium, magnesium, selenium, sodium, zinc and phosphorous (Watson, 2008). However, eggs are highly perishable and can rapidly lose their quality due to loss of moisture and carbon dioxide through nearly 10,000 tiny pores. These pores in the eggshell also facilitate the penetration of certain microorganisms into the interior of eggs and contaminate the internal content (Van Immerseel, Nys, & Bain, 2011).
Currently in food industry variety of methods are used for decontaminating the surface of eggs, such as dry cleaning or washing with water which usually containing a sanitizing agent (e.g., sodium hypochlorite). Washing of shell eggs for retail sale is a common practice with on-line systems in the United States, Canada, Australia, and Japan. However, this method is a matter of continuous debate. Eggshell washing is usually followed by chilled storage. This method could damage the cuticle which may favor moisture loss and transmission of bacteria through the shell. On the other hand, thermal pasteurization is not applicable to the whole shell egg because the heat would simply cook the egg (Caudill et al., 2010). This is why non-thermal processing methods such as electron beam has been suggested as an alternative method of preservation for the whole shell egg quality and safety. However, irradiation under aerobic conditions caused the development of off-flavor and undesirable radiation-induced oxidative changes in whole egg powder and egg yolk solids at >3 kGy (Tahergorabi, Matak, & Jaczynski, 2012).
To overcome the aforementioned problems, considerable attention has been given to the development of edible coating materials for preservation of eggs, from polysaccharides, proteins, or lipids, or their blends (Rhim et al., 2004, Xie et al., 2002, Knight et al., 1972, Yüceer and Caner, 2014, Waimaleongora-Ek et al., 2009). An edible coating has been defined as a harmless (edible) thin layer of food materials that is directly formed on food surfaces (Ananey-Obiri et al., 2018). Therefore, the edible coating is recognized as Generally Recommended as Safe (GRAS). Such coatings prevent the penetration of micro-organisms into shell eggs. As a result, they extend their storage time and reduce economic losses. Earlier studies concluded that the coatings helped maintain interior quality, add strength to shell, and reduce microbial load on the shell surface (Falguera, Quintero, Jiménez, Muñoz, & Ibarz, 2011). To the best of our knowledge, no literature information is available that comprehensively reviews the edible coating materials used for improving shelf life of eggs. This review article discusses the quality and safety of eggs and summarizes research findings on the effectiveness of and the problems associated with various types of coatings.
Section snippets
External structure of hens’ eggs
The shape of an avian egg is usually oval and is represented as shape index. Shape index is the ratio between the diameter and the length of an egg. The shape index of an avian egg usually ranges from 0.65% to 0.85% (Li-Chan & Kim, 2008). The structures of avian eggs are similar across various species. Birds are oviparous and produce cleidoic eggs. The contents inside the egg are isolated from the external environment. The eggs contain all the essential nutrients for the developing embryo and
Internal structure of hens’ eggs
Hens’ eggs are comprised of 59% egg white and 31% egg yolk by weight. The eggshell makes up the remaining 10% of a hen’s egg. The egg yolk is released from the ovary into the oviduct during ovulation. The oviduct secretes various components that help to form the vitelline membrane, egg white and shell membranes that surround the mature egg yolk (Li-Chan & Kim, 2008). The pituitary gland interacts with the ovary and controls different steps in egg formation. Domestic hens produce almost 300 eggs
Assessment of the quality of hens’ eggs
Avian eggs are an important food staple around the world. The nutritional value of a hen’s egg is well acknowledged by scientists and nutritionists. However, avian eggs have to compete with other food items for sales and marketing in the modern food industry (Roberts, 2004). The nutritional quality and viability of avian eggs are areas of major concern in the food processing and food packaging industry. The major disadvantages of avian eggs include high fragility and loss of essential nutrients
Grade of eggs
Grade requirements are set for table eggs in order to protect consumers from health risks. In grading eggs, factors like interior quality, weight, cleanliness and shell integrity are determined. Table eggs are graded across registered egg stations in order to ensure the safety of packaged eggs. Eggs that are graded as “A” are clean and free from cracks. Moreover, they do not impose an additional risk to consumers. The gradation of eggs deteriorates with the presence of cracks and leaks. In an
Safety and microbiology of eggs
Microbial contamination is a key concern that limits the consumption of table eggs. Hence, table eggs should be appropriately decontaminated before they are used as food items. The regulatory guidelines aim to reduce exogenic and endogenic contamination of table eggs.
Various microorganisms are responsible for the contamination of eggs and egg products. Contamination of eggs and egg products with microorganisms predisposes the risk of various infectious diseases in humans. In Europe, Salmonella
Edible coatings
Edible coatings are often used to extend the shelf-life and quality of foods during storage. The major edible coatings that are used in the food processing industry are protein-based, lipid-based, and polysaccharide-based. Polysaccharide-based coatings are preferred due to their low-thickness, high flexibility, and greater transparency (Pavlath & Orts, 2009). Summary of application of different types of edible-coatings that were used for the egg quality and safety preservation are given in
Challenges associated with industrial application of edible coatings
Although edible coatings have been successfully used on eggs at lab-scale level. However, there are still some challenges to upscaling the edible coatings for industrial applications. According to USDA and European regulations, edible coatings are considered as food ingredients and food additives. Therefore, the materials used for this purpose must be non-toxic, food grade and the whole process of coating should be conducted under high standard hygiene. Also, many materials used for edible
Conclusions
Eggs are nutritious food commodity that are consumed all around the world. However, they are susceptible to quality losses and bacterial contaminations from different routes. Therefore, it is logical to devise a strategy to maintain the quality and safety of eggs during storage time. Various types of edible coating have been used for this purpose. Most of the developed edible coatings have been used at the lab-scale level. Further research is needed to present the numerous benefits that edible
Declaration of Competing Interest
The authors declare no conflict of interest.
Acknowledgment
This work did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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