Proteins

Question 1

what is the driving force for hydrophobic attraction?

Answer 1

the driving force is the disruption of water molecules near the exposed surfaces of hydrophobic molecules.

Question 2

why is the transfer of hydrocarbons from non-polar solvents to water not thermodynamically favourable?

Answer 2

the Gibbs free energy is positive.

Question 3

what are the amino acids with hydrophobic groups?

Answer 3

glycine, alanine, proline, valine, phenylalanine, tryptophan, leucine, isoleucine, methionine

Question 4

what is the Gibbs free energy for hydrophilic amino acids?

Answer 4

negative

Question 5

what is the Gibbs free energy for hydrophobic amino acids?

Answer 5

positive

Question 6

What is the shape of hydrophilic proteins?

Answer 6

they have an elongated or rod shape because the shape has a larger surface area to volume ratio, which enables many hydrophilic residues to be placed on the surface.

Question 7

what is the shape of globular proteins?

Answer 7

a globular shape will minimize the surface area to volume ratio, enabling more residues to stay hidden in the protein interior.

Question 8

what is protein solubility?

Answer 8

it is the percentage of the total amount of protein contained in a food material that can be extracted with water or a salt solution.

Question 9

what are the factors that influence protein solubility?

Answer 9

hydrophobic interaction (protein-protein interactions)
ionic interactions (protein-water)

Question 10

what is ionic strength?

Answer 10

it is a measure of the total concentration of charge contributed by ions present in a solution.

Question 11

what is salting in?

Answer 11

as the salt concentration in a protein solution increases, the additional counter ions more effectively shield the ionic charges of the protein molecule. this increased protein solubility with an increase in ionic strength.

Question 12

what is salting-out?

Answer 12

at high salt concentration, the bulk of the solvent molecules solvate the ion in solution. therefore, there is not enough solvent to dissolve the protein molecules. the protein molecules will clump together and precipitate out of the solution.

Question 13

what is the isoelectric point?

Answer 13

it is the point at which the protein have no charge.

Question 14

why is there minimum solubility at the isoelectric pH?

Answer 14

this is mainly due to the lack of electrostatic repulsion, which promotes aggregation and precipitation via hydrophobic interaction.

Question 15

at what pH are protein extractions carried out?

Answer 15

at pH 8-9 since most proteins are highly soluble at an alkaline pH.

Question 16

what is water-binding capacity?

Answer 16

it is the number of grams of water-bound per gram of protein when a dry protein powder is equilibrated with water vapour at 90-95% relative humidity.

Question 17

what are the factors influencing WBC?

Answer 17

pH, ionic strength, type of salts, temperature, protein conformation, amino acid composition, surface hydrophobicity.

Question 18

why is WBC important?

Answer 18

the ability of proteins to entrap water is associated with the juiciness and tenderness of comminuted meat products and desirable texture of bakery and gel products.