Topic 6: Eggs Flashcards
at what speed does water vapor move in room temp
500 ms-1
Composition of an egg includes
Shell (CaCO3), shell membrane, chalazae (twisted strands that hold the yolk centered), albumen (egg white, water and protein, 60% of egg weight) Yolk (nutrient rich, fats proteins vitamins and minerals 30% of egg weight)
what are the 3 main proteins found in egg whites?
ovalbumin (quality of egg), conalbumin (protects against bacterial contamination), ovomucoid (resistant to denaturation)
egg yolk composition
water, protein, lipids (lecithin are surface active agents that help with the emulsion), nutrients
temperature of coagulation in eggs?
57.8-61.1 C: egg white is in liquid form but starts to whiten
62.2 C : conalbumin denatures and egg white starts to form a loose gel
64.4 C : the protein livetin denatures and egg yolk starts to form tender gel
protein denaturation in eggs?
disrupts the normal alpha helix and beta sheets and uncoils the proteins. this denaturation also plays a role in causing coagulation to occur in the eggs
heat denatures proteins when frying an egg (weakens hydrogen bonds among polypeptide chains) egg white hardens and new bonds are formed
What happens to egg whites proteins when whipped?
foams up with bubbles and cause the egg whites to look opaque.
During the whipping process proteins will also denature when air s introduced, where the hydrophobic amino acids stick to air and the hydrophilic stick to water. This forms a mesh network that holds air bubbles in a sea of water
Stages of whipped egg whites?
foamy – still liquidy but has some bubbles and starts to become an opaque white
soft peaks – the egg whites are fully white and hold it shape
stiff peaks – when the whisk is lifted out of the egg whites, the peak stands erect and doesn’t bend
dry peaks – the matrix of proteins begins to break down, and foam collapses and turns white, grainy, water and flat (overbeaten and can’t be salvaged)
what are some examples of stabilizers for whipped egg whites?
stabilizers help delay the collapse of air bubbles examples are sugar, and cream of tartar
sugar slows drainage of water from the air bubbles, sugar is best added during the soft peak stage
Cream of tartar - acid alters the electric charge of egg white proteins reduces interaction of protein molecules. It may delay foaming but results in stable foam
Examples where protein is denatured by acids, bases or salts
century eggs - proteins denatured by bases, duck egg coated in rice bran and calcium oxide
eggs, pig trotters in ginger and sweetened vinegar - protein denatured by acidic medium, hardens eggs
salted egg - duck eggs denatured with salt ions
others: tea eggs, Chinese marinade egg, iron eggs or Tiedan
what happens when an egg is immersed in vinegar?
Calcium carbonate reacts with acetic acid to create calcium ethanoate and carbon dioxide, eggshell dissolves, and egg protein is denatured and rubbery
CaCO3 + 2CH3COOH –> 2CH3COOC + CO2 + H2O
