The quality of shell eggs is described by external and internal factors. External factors refer to the strength, texture, porosity, shape, cleanliness, soundness, and color of the shell, whereas internal factors refer to the presence of inclusions (blood and meat spots, and chalazae), the quality of the albumen, the color and uniformity of the yolk, and the odor and taste of the egg. Extrinsic factors affecting shell quality include temperature, hen age, and nutrition. Loss of shell egg quality begins immediately after the egg is laid, due to water loss, which leads to thinning of the albumen and an increase in the size of the air cell. Furthermore, due to migration of carbon dioxide from the egg, an increase in albumen pH occurs as well as a decrease in the strength of the vitelline (yolk) membrane. Off-flavors and odors associated with eggs may be caused by the ration fed to the hens.
Loss of shell egg quality may also occur as a result of microbial growth (i.e., spoilage). Freshly laid eggs may be contaminated through two primary routes: transovarian or trans-shell infection. Transovarial transmission occurs when bacteria infect the hen's ovaries or oviducts, resulting in contamination of the egg during its formation. The more common route of microbial contamination of eggs, however, is via trans-shell infection. This occurs when the physical (e.g., the cuticle, shell, and shell membranes) and chemical (e.g., lysozyme) antimicrobial barriers of the egg are compromised, resulting in contamination of the internal contents of the egg.[2,5] Microorganisms contaminating the egg after laying originate from the intestines when the egg passes through the cloaca, as well as from nest materials, litter, or incubator surfaces. The rate at which microorganisms penetrate the egg depends on factors such as storage temperature, age of the eggs, and level of contamination.1-3-1
The most common form of bacterial spoilage of eggs is rotting, caused primarily by Gram-negative bacteria; the type of rot depends on the bacterial species/strain(s) present. For example, fluorescent green rots are caused by Pseudomonas putida; fluorescent blue rots by Pseudomonas aeruginosa; pink rots by Pseudomonas fluores-cens; colorless rots by Acinetobacter/Moraxella spp.; black rots by Proteus vulgaris, Aeromonas liquefaciens, and species of Pseudomonas, Alcaligenes, and Enter-obacter; and red rots by Serratia marcescens.[2,3,5] Mold spoilage of eggs may also occur during refrigerated storage when the humidity is high. Growth of molds on the egg surface is referred to as whiskers and is often associated with Cladosporium herbarum, whereas pinspots are caused when fungal (mycelia) growth occurs inside the egg.[2,3-
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