Unit 4 : Food Chemistry - Protein

Question 1

Describe the structure of a protein

Answer 1

• Chains of amino acids linked with peptide bonds

Question 2

Describe the structure of an amino acid

Answer 2

• Amino acids are linked by peptide bonds formed between amino and carboxylic acid groups of neighbouring amino acids in the polypeptide sequence

Question 3

What are the four levels of protein structure ?

Answer 3

• Primary
• Secondary
• Tertiary
• Quaternary

Question 4

Describe the primary protein structure

Answer 4

• Linear structure and indicates the sequence of amino acids in the chain

Question 5

Describe the secondary structure

Answer 5

• The backbones of a amino acids in a polypeptide chain form hydrogen bonds with one another leading to the folding of the chain.
• Two kinds , alpha helix and beta sheets

Question 6

Describe the tertiary structure

Answer 6

• side chains of amino acids in a polypeptide chain interact with one another and lead to the folding of the beta sheets or alpha helixes.

Question 7

Describe the quaternary structure

Answer 7

• Many proteins are formed from multiple polypeptide chains .

Question 8

What is denaturation of proteins mean ?

Answer 8

• It is reversible or irreversible change in the protein shape

Question 9

How does pH denature proteins ?

Answer 9

• Hydrochloric acid is produced in our stomach primarily to denature the food proteins

Question 10

How does heat denature proteins ?

Answer 10

• Heating an egg denatures its proteins leading to solidification of the egg.

Question 11

How does alcohol denature proteins ?

Answer 11

• When alcohol is consumed, it penetrates our cells and denatures cell proteins

Question 12

How does UV radiations denature proteins ?

Answer 12

• Exposure to strong UV radiations causes denaturation of some of the proteins in our skin cells

Question 13

How does heavy metals denature proteins ?

Answer 13

• Mercury can denature our cell proteins and thus ingesting mercury by accident leads to mercury poisoning

Question 14

What are the water holding capacity and solubility of proteins ?

Answer 14

• depends on the pH of the medium and the type of amino acids
• when the protein has a net charge of 0 , the pH is called isoelectric point and it is least soluble and has the lowest water holding capacity, because at his pH proteins shrink and start losing their water

Question 15

Where are actin and myosin found ?

Answer 15

they are major proteins found in myofibrils

Question 16

Where are collagen and elastin found ?

Answer 16

• Connective tissues

Question 17

How does proteins affect the texture ?

Answer 17

• They provide the fibrous texture of meat

Question 18

How does proteins affect gelation?

Answer 18

• Some proteins solublize when heated with water, upon cooling they form a gel

Question 19

How does proteins affect color in food ?

Answer 19

• Some proteins impart color to the food
• oxymyogloblin which is bright red in color
• Metmyoglobin is brown in color

Question 20

How does proteins affect emulsification and fat holding capacities?

Answer 20

• Milk protein casein is an emulsifier that is often added to processed meat products such that fat doesn’t separate from the food

Question 21

What are some foaming properties of protein ?

Answer 21

• Main protein in egg white is ovalbumin which has the higher foaming capacity, which is why eggs are added in cakes, meringue and several other baked goods when a spongy product is desirable

Question 22

how is gluten made?

Answer 22

• Wheat Proteins called gliadins and glutenins together from a viscoelastic structure called gluten