Flashcards in Properties of Proteins Deck (32)
List the properties of proteins
What is denaturation?
A change in the nature of a protein chain
It involves the unfolding of a protein chain which results in an irreversible change in shape
One this happens the protein often coagulates (sets or becomes hard)
How does denaturation result in coagulation?
Denaturation involves the unfolding of a protein chain which results in an irreversible change in shape which often results in coagulation
What means bring about denaturation?
How does heat bring about denaturation?
Heat causes protein chains to unfold and bond together which causes food to coagulate
How do chemicals bring about denaturation?
By lowering or raising pH levels by the addition of acids or alkalis a protein's structure can be denatured
How does mechanical action bring about denaturation?
Mechanical action such as whipping or beating causes protein chains to unfold and brings about partial coagulation
How do enzymes bring about denaturation?
Enzymes cause a change to the nature of a protein's structure
Give a culinary use of denaturation brought about by heat
Egg whites coagulate and change from translucent to opaque at 60 degrees Celsius and egg yolks coagulate at 68 degrees Celsius
Give a culinary use of denaturation brought about by chemicals
A vinegar-based marinade tenderises meat by denaturising proteins
Give a culinary use of denaturation brought about by mechanical action
Whipping of eggs when making a sponge cake
Give a culinary use of denaturation brought about by enzymes
The enzyme rennin in rennet causes caseinogen in milk to coagulate during the making of cheese
Describe the elastic property of proteins
Some fibrous proteins such as gluten in wheat are quite elastic
Give a culinary use of the elastic property of proteins
Gluten makes yeast dough elastic enough to trap the carbon dioxide gas produced by yeast which helps it rise
Describe the Maillard reaction in proteins
This is the non-enzymic browning of food.
It occurs when an amino acid reacts with a carbohydrate (sugar) under dry heat
What does the Maillard reaction occur between?
An amino acid and a carbohydrate (sugar)
Under what condition does the Maillard reaction occur?
Give a culinary application of the Maillard reaction of proteins
It gives an attractive brown colour to foods such as shortbread biscuits and roast potatoes
Describe the solubility property of the Maillard reaction
Most proteins are insoluble in water, apart from collagen in meat (soluble in hot water) and egg albumin (soluble in cold water)
Give a culinary use of the solubility property of the Maillard reaction
Moist heat tenderises meat by converting collagen to gelatine
Describe the gel formation property of a protein
When collagen (protein present in the bones and skin of meat) is heated it is converted to gelatine
Gelatine can absorb large amounts of water when heated as protein chains uncoil and water becomes trapped
This forms a sol and on cooling it forms a gel which is a semi-solid viscous solution with a three dimensional protein matrix in which water molecules become trapped
What happens to collagen when it is heated?
It is converted into gelatine
What protein is converted to gelatine when it is heated?
What property does gelatine have that is used in the setting of jam?
Gelatine can absorb large amounts of water when it is heated
How does gelatine absorb large amounts of water?
When gelatine is heated it's protein chains uncoil and water becomes trapped
What is formed when gelatine absorbs a large quantity is absorbed
A sol is formed
What is formed when a sol is cooled?
What is a gel?
A semi-solid viscous solution
How is a gel formed?
When gelatine is heated it absorbs water to form a sol which when cooled forms a gel which is a semi-solid viscous solution