Unit 4 : Food Chemistry - Protein Flashcards
Describe the structure of a protein
- Chains of amino acids linked with peptide bonds
Describe the structure of an amino acid
- Amino acids are linked by peptide bonds formed between amino and carboxylic acid groups of neighbouring amino acids in the polypeptide sequence
What are the four levels of protein structure ?
- Primary
- Secondary
- Tertiary
- Quaternary
Describe the primary protein structure
- Linear structure and indicates the sequence of amino acids in the chain
Describe the secondary structure
- 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
Describe the tertiary structure
- 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.
Describe the quaternary structure
- Many proteins are formed from multiple polypeptide chains .
What is denaturation of proteins mean ?
- It is reversible or irreversible change in the protein shape
How does pH denature proteins ?
- Hydrochloric acid is produced in our stomach primarily to denature the food proteins
How does heat denature proteins ?
- Heating an egg denatures its proteins leading to solidification of the egg.
How does alcohol denature proteins ?
- When alcohol is consumed, it penetrates our cells and denatures cell proteins
How does UV radiations denature proteins ?
- Exposure to strong UV radiations causes denaturation of some of the proteins in our skin cells
How does heavy metals denature proteins ?
- Mercury can denature our cell proteins and thus ingesting mercury by accident leads to mercury poisoning
What are the water holding capacity and solubility of proteins ?
- 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
Where are actin and myosin found ?
they are major proteins found in myofibrils
Where are collagen and elastin found ?
- Connective tissues
How does proteins affect the texture ?
- They provide the fibrous texture of meat
How does proteins affect gelation?
- Some proteins solublize when heated with water, upon cooling they form a gel
How does proteins affect color in food ?
- Some proteins impart color to the food
- oxymyogloblin which is bright red in color
- Metmyoglobin is brown in color
How does proteins affect emulsification and fat holding capacities?
- Milk protein casein is an emulsifier that is often added to processed meat products such that fat doesn’t separate from the food
What are some foaming properties of protein ?
- 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
how is gluten made?
- Wheat Proteins called gliadins and glutenins together from a viscoelastic structure called gluten
