Egg quality and safety with an overview of edible coating application for egg preservation

Highlights

• Eggs are inexpensive source of high-quality protein.

• Eggs are susceptible to quality loss and microbial contaminations.

• Edible coatings are able to maintain the quality and safety of eggs.

Abstract

Eggs are staple food in the human diet and are consumed globally. They represent a complete food required for well-being and are recognized by consumers as versatile and wholesome with a balance of essential nutrients. However, eggs are perishable and susceptible to contamination with certain microorganisms. Past studies concluded that edible coatings have been successful to maintain the interior quality and reduce the microbial load on the eggshell surface. This paper provides an overview of the egg quality and safety and discusses the application of various types of lipid-, polysaccharide-, and protein-based edible coating systems on eggs. Edible coatings could be a viable alternative to existing techniques for maintaining the internal quality and safety of fresh eggs during long-term storage.

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.