EGGS AND EGG PRODUCTSCHAPTER 4

INTRODUCTION

Eggs provide a complete diet for the developing chick embryo and serves as the principal source of food for the first few days of the baby chicks

It contains all the nutrients for a complete individual - the most complete food in the human diet

Eggs are sterile when laid, ready-packaged in a shell, and afford protection from contamination

PROPERTIES OF EGG

COMPOSITION OF EGG

The % of several parts of the egg of chicken, duck, turkey and quail are in following table

% composition of egg contents varies among different species of birds. Yolk size and amount of albumen have been shown to vary with season and age of layer

NUTRITIVE VALUE OF EGG

Eggs are composed of proteins, fats, carbohydrates, minerals and vitamins

These are distributed among the egg component structures in a very specific manner

PROTEIN

The chief source of protein is albumen and yolk

Only a small amount is present in the shell membrane. The various parts of the average chicken egg contains the following amounts of protein

9. Ovalbuminoid

9 different proteins in egg

About 18 amino acids have been found in the egg proteins – more remain to be discovered

The proportional amount of these amino acids in chicken and duck egg is as below:

FATS

The presence of a variety of fats and fat like substances provide high energy value

4 main types of egg fats:1) True fat (glycerides) 3.8 g (62.3%)2) Phospholipids 2.0 g (32.8%)

a) Ovolecithinb) Ovocephalinc) Ovosphingomyelin

3) Sterols (cholesterol) 0.3 g (4.9%)4) Cerebrosides (traces)

a) Ovophrenosinb) Ovokerasin

Of the 6.2 g of fat in eggs, about 99% is present in the yolk!

CARBOHYDRATES

The egg contains only 1% of carbohydrate of the total egg content

The energy values of the egg varies because of the species and egg size

MINERALS

Minerals are essential and needed in small quantity

Eggs offer excellent source of many major and trace minerals:

Major minerals – calcium, phosphorus, magnesium, potassium, chlorine, sodium, sulphur, iron

Trace minerals – zinc, copper, bromine, manganese, iodine (↓ amount found)

VITAMINS

Vitamins in eggs are grouped as:a) Fat soluble vitamins: vit A, D, E, Kb) Water soluble vitamins: thiamine,

riboflavin, niacin, pantothenic acid, inositol, pyridoxine, folic acid, choline

PRESERVATION EGG PRODUCTS

Salted duck egg The simplest method to preserve an egg is to treat

it with salt. Salt draws water out of bacteria and molds, which prevents their growth. The Chinese salted duck egg is made by immersing duck eggs in brine, or coating them individually with a paste of salt and mud or clay. The eggs stop absorbing salt after about a month, having reached osmotic equilibrium.Their yolks take on an orange-red color and solidify, but the white remains liquid. They are boiled before consumption, and are often served with rice congee.

PICKLED EGGS

Another method is to make pickled eggs, by boiling them first and immersing them in a mixture of vinegar, salt, and spices, such as ginger or allspice. Frequently, beetroot juice is added to impart a red colour to the eggs. If the eggs are immersed in it for a few hours, the distinct red, white, and yellow colours can be seen when the eggs are sliced. If marinated for several days or more, the red colour will reach the yolk. If the eggs are marinated in the mixture for several weeks or more, the vinegar will dissolve much of the shell's calcium carbonate and penetrate the egg, making it acidic enough to inhibit the growth of bacteria and molds. Pickled eggs made this way will generally keep for a year or more without refrigeration.

Century egg

A century egg or hundred-year-old egg is preserved by coating an egg in a mixture of clay, wood ash, salt, lime, and rice straw for several weeks to several months, depending on the method of processing. After the process is completed, the yolk becomes a dark green, cream-like substance with a strong odor of sulfur and ammonia, while the white becomes a dark brown, transparent jelly with a comparatively mild, distinct flavor. The transforming agent in a century egg is its alkaline material, which gradually raises the pH of the egg from around 9 to 12 or more. This chemical process breaks down some of the complex, flavorless proteins and fats of the yolk into simpler, flavorful ones, which in some way may be thought of as an "inorganic" version of fermentation.

EGGS STORAGE

1. Temperature -1oC and 80% relative humidity is ideal for egg. It could last for 6 months storage. After some time the egg lose carbon dioxide through porous shell, making the egg more alkaline

2. The loss of CO2 also associated with staling process

3. Storing egg under CO2 could minimize the problem

FREEZING EGGS1. Frozen liquid egg one of suitable

preservation technique. At temperature -30oC freezing may take from about 48-72 hours. Addition of 5% glycerin to egg yolk is one way to avoid gelation to egg yolk during freezing. Sugar and salt may be added respectively

2. Drying of egg : whole, white or yolk after pasteurization may be dried by any of several methods, including spray drying, tray drying, foam drying or freeze drying

3. Maillard browning reaction – between glucose and protein in egg white. Desugaring process is practiced prior to drying in order to avoid browning of egg white