2009_Book_FoodChemistry

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