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11.4 Egg Products 557

11.2.4.4.4 Aroma Substances

The typical aroma substances of egg white and

egg yolk are still unknown. The “fishy” aroma defect

that can occur in eggs is caused by trimethylamine

TMA, which has an odor threshold that

depends on the pH (25 µg/kg, pH 7.9) because

only the undissociated form is odor active. TMA

is formed by the microbial degradation of choline,

e. g., on feeding fish meal or soy meal. Normally,

TMA does not interfere because it is enzymatically

oxidized to odorless TMA oxide. However,

in feed, e. g., soy meal, substances exist which

could inhibit this reaction.

11.2.4.4.5 Colorants

The color of the yolk, which is produced by

carotenoids in the feed, is considered to be

a quality characteristic. Normally, xanthophylls

(cf. 3.8.4.1.2) are absorbed from the feed, preferably

lutein, followed by luteinmono- and diester,

3 ′ -oxolutein and zeaxanthin. The color of the

yolk can be intensified by the appropriate feed

composition. The substances available dissolved

in an oil are, e. g., β-apo-8 ′ -carotene ethyl ester,

citranaxanthin (5 ′ ,6 ′ -dihydro-5 ′ -apo-β-carotene-

6 ′ -one, Formula 11.5) and canthaxanthin.

11.3 Storage of Eggs

(11.5)

A series of changes occurs in eggs during

storage. The diffusion of CO 2 through the pores

of the shell, which starts soon after the egg is

laid, causes a sharp rise in pH, especially in

egg white. The gradual evaporation of water

through the shell causes a decrease in density

(initially approx. 1.086 g/cm 3 ; the daily reduction

coefficient is about 0.0017 g/cm 3 )andthe

air cell enlarges. The viscosity of the egg white

drops. The yolk is compact and upright in a fresh

egg, but it flattens during storage. After the egg

is cracked and the contents are released onto

a level surface, this flattening is expressed as

yolk index, the ratio of yolk height to diameter.

Furthermore, the vitellin membrane of the yolk

becomes rigid and tears readily once the egg is

opened. Of importance for egg processing is the

fact that several properties change, such as egg

white whipping behavior and foam stability. In

addition, a “stale” flavor develops.

These changes are used for determination of the

age of an egg, e. g., in the floating test (change in

egg density), flash candling (egg yolk form and

position), egg white viscosity test, measurement

of air cell size, refractive index, and sensory

assay of the “stale” flavor (performed mostly

with softboiled eggs). The lower the storage

temperature and the lower the losses of CO 2 and

water, the lower the quality loss during storage

of eggs. Therefore, cold storage is an important

part of egg preservation. A temperature of 0 to

−1.5 ◦ C (common chilled storage or subcooling

at −1.5 ◦ C) and a relative humidity of 85–90%

are generally used. A coating (oiling) of the shell

surface with light paraffin-base mineral oil quite

efficiently retards CO 2 and vapor escape, but

a tangible benefit is derived only if oil is applied

soon (1 h) after laying, since at this time the CO 2

loss is the highest. Controlled atmosphere storage

of eggs (air or nitrogen with up to 45% CO 2 )

has been shown to be a beneficial form of egg

preservation. Cold storage preserves eggs for 6–9

months, with a particularly increased shelf life

with subcooled storage at −1.5 ◦ C. Egg weight

loss is 3.0–6.5% during storage.

Microbial spoilage is indicated by an increase

in lactic acid and succinic acid to values above

1g/kg and 25 mg/kg of dry matter respectively.

3-Hydroxybutyric acid serves as an indicator of

fertilized eggs (>10 mg/kg of egg mass).

11.4 Egg Products

11.4.1 General Outline

Egg products, in liquid, frozen or dried forms,

are made from whole eggs, white or yolk. They

are utilized further as semi-end products in

the manufacturing of baked goods, noodles,

confectionery, pastry products, mayonnaise and

other salad dressings, soup powders, margarine,

meat products, ice creams and egg liqueurs.

Figure 11.5 gives an overview of the main

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