2.1. Functional properties of proteins in foods

Question 1

What are proteins?

Answer 1

-Long chains of amino acids

Question 2

describe the structure of protein

Answer 2

-Consist of amino acids which are made up of carbon (C), hydrogen (H), oxygen (O) and nitrogen, (N)
-The radical (R) group is the part of the amino acid that makes it different from other amino acids.

Question 3

Difference between peptide/dipeptide and polypeptide bonds

Answer 3

peptide-when the amino group of one amino acid can link with the acid group of another amino acid group to form a chain of amino acids
dipeptide- when two amino acids are joined together
polypeptide- When many amino acids are joined together

Question 4

Draw the general structure of an amino acid?

Answer 4

on RC

Question 5

Draw the formation of a peptide bond?

Answer 5

on RC

Question 6

What are the 2 structures of protein (give examples)

Answer 6

• fibrous protein (meat, chicken, fish, wheat and baked products)
• globular protein (eggs, milk, yoghurt, cheese, cream)

Question 7

Describe fibrous proteins?

Answer 7

-straight and elongated
- coiled or spring like (elastic proteins eg,gluten-can be pulled out of shape but will return to original shape) or straight (inelastic proteins eg. Gristle’ in meat)

Question 8

Describe globular proteins?

Answer 8

-have a 3 three dimensional shape. –rounded in shape and examples include: ovalbumin in eggs. Caseinogen in milk and haemoglobin in meat.

Question 9

when do denaturation and coagulation occur?

Answer 9

when protein is altered by: heat, mechanical agitation, acids or salts and enzymic action.

Question 10

What happens during denaturation and what is it caused by?

Answer 10

-Strands of protein arrange themselves in a helix shape.
-Denaturation occurs when
the bonds that hold the helix structure break down
- causes the strands to separate and unravel.
This separation is caused by 5 factors:
-The application of temperature e.g. frying beef steak
-Mechanical agitation e.g. whisking egg white
-Acidity e.g. making sour cream and yoghurt
-Enzymes e.g. marinating meats
-Salt e.g. poaching eggs with salted water

Question 11

Difference of denaturation for globular and fibrous protiens?

Answer 11

-occurs in globular proteins more easily and is more easily visible
-Denaturation in fibrous proteins will occur over time

Question 12

Describe what coagulation is what happens during the process

Answer 12

-is when a denatured protein separates from other nutrients and turns from a liquid to a solid.
-occurs after denaturation
- the bonds holding the helix shape break apart and coagulation of protein occurs.
-The denatured proteins start to rejoin, forming a different structure and a solid mass.

Question 13

What is the consequences of coagulation?

Answer 13

-It’s irreversible as the proteins cannot be turned back into their liquid form
-if it continues for too long overcoagulation will occur where the proteins shrink and toughen forcing liquid out from inside the proteins

Question 14

What is the gelation of proteins and give examples?

Answer 14

the process of gel formation and it occurs after coagulation.
-can occur in both proteins and carbohydrates however the gelation of proteins occurs when tiny droplets of liquids become trapped within coagulated proteins, this forms soft elastic foods such as custard, junket and cheese. Gelation is reversible

Question 15

What are gels ad what must be present for them to form by gelation

Answer 15

-an elastic solid
-Either heat, acids and enzymes must be present

Question 16

what is gelatine and what happens when it’s mixed with warm water and then cooled?

Answer 16

-is a protein extracted from connective the tissues present in meat,
-When gelatin is mixed with warm water the protein molecules start to unwind. When the gelatine mixture is cooled a stable network is formed

Question 17

what are colloid structures?

Answer 17

-formed when different ingredients are mixed together

Question 18

how is a gel an example of a colloid structure?

Answer 18

eg.jams and jellies
-is formed when a liquid is mixed into a solid (water/juice in fruit)

Question 19

globular proteins in milk and dairy?

Answer 19

-caseinogen, lactalbumin and lactoglobulin
-denature very easily as when in a pH less than 7 proteins will denature because the acid breaks down the the salt bridges between the amino acid strands.

Question 20

Effects of cooking and heat on the proteins in milk and dairy examples ?

Answer 20

making soured cream or yoghurt- a bacterial culture creates acidic conditions by producing lactic acid which causes milk the protein caseinogen to coagulate and develop a slightly sour taste.
-coagulation of milk protein-when milk is heated to just below boiling point a skin forms and this is due to the coagulation of milk protein.
-cheese-making- involves coagulation of protein by the addition of enzymes. The enzyme used in cheesemaking is rennin which is used in the form of rennet.

Question 21

How is the desired texture and flavour produced in cheesemaking?

Answer 21

-through the use of enzymes, agitation, heat and salt

Question 22

What effect does cooking have on eggs, in particular the protein in eggs?

Answer 22

-Eggs contain globular proteins. When egg is heated the egg white (albumen) and egg yolk (vitellin and vitellenin) which is the major source of protein) turn solid.
-The proteins start to thicken, by coagulation. Egg whites coagulate at 60°C, egg yolks 65°C, with full coagulation occurring at 70°C.

Question 23

What factors can the process of egg whites forming foams be affected by?

Answer 23

• Temperature: more aerated foams are formed from room temperature eggs.
• Acids: acids such as cream of tartar slows the formation of foam but increases foam stability
  -Agitation: the faster the whisking the finer the final foam
  -Addition of other ingredients eg.
  fat (egg yolk) prevents foam forming
  water increases volume but decreases stability
  sugar added towards the end of whisking makes the foam shinier, finer and more stable

Question 24

What is the effect of marinating on the proteins in meat?

Answer 24

-Meat proteins are fibrous proteins and the denaturation of protein is less visible, however given time the fibrous protein denature by marinating meat in an acid overnight to tenderise it.
-The addition of an acid such as lemon juice or vinegar before cooking denature the protein collagen.

Question 25

What effect does enzymes have on meat?

Answer 25

-Can be used to tenderise meat
-found naturally in meat and can denature tough protein chains and this aging process can take a few days. Bromelain, an enzyme found in pineapple juice denatures the proteins myosin, collagen and elastin when meat is marinated.

Question 26

What effect does adding heat to meat have on the proteins?

Answer 26

• leads to meat proteins coagulating and shrinking.
  -The heat causes the muscles fibres to lose water, and solidifying At around 60°C meat protein begins to denature and the muscle fibres become firmer.
• At above 60°C the meat protein shrinks and the meat juices are squeezed out and if meat is cooked for too long the meat can become chewy.

Question 27

When does the Maillard reaction occur?

Answer 27

-when dry heat is applied to a food that contains both protein and sugar
-eg. Cooking processes including baking, roasting, grilling, barbecuing and frying foods that contain a protein and sugar

Question 28

What is the Maillard reaction characterised by and what does it do?

Answer 28

-a dark yellow to brown crust on cooked food e.g. roast meat, bread, cake, cereals and french fries.
-adds to the sensory appeal of these foods e.g. the crust of bread or the crispy outside skin on roast chicken.

Question 29

What is gluten and how is it formed?

Answer 29

-a protein found in grains such as wheat, rye and barley. - is composed of glutenin and gliadin.
- when water is added to flour the glutenin and gliadin form gluten

Question 30

What is bread dough made up of

Answer 30

a mixture of flour (usually wheat which can be mixed with other grains such as rye), yeast, salt and a liquid (often this is water).

Question 31

What is the role of gluten in bread making?

Answer 31

-When dough is mixed and kneaded is becomes more elastic and stretchy. Kneading strengthens the gluten strands and the network of gluten strands get stronger and longer.
- if too much gluten is formed by over kneading the bread to become tough and chewy because
-When bread dough rests or relaxes the elasticity of the dough is reduced which makes it easier to roll out and shape.