3.3.2.1.1 Protein denaturation and coagulation Quiz: AQA Food Preparation and Nutrition, Unit 2

The 20 questions

1. What is meant by protein denaturation during cooking?

   • Protein molecules join onto starch granules, thickening the liquid around them
   • Protein molecules are broken into their individual amino acids by contact with water
   • Protein molecules change shape and unfold, often when heated, acidified or whisked
   • Protein molecules dissolve completely into fat, which makes the food look glossy

2. Which term describes denatured protein molecules linking together to form a firm, set structure?

   • Coagulation
   • Caramelisation
   • Emulsification
   • Gelatinisation

3. A cook marinates chicken in lemon juice. What does the acid most likely do to the chicken protein?

   • It caramelises the protein, so the surface turns brown and bitter before cooking
   • It gelatinises the protein, so the surface thickens into a glossy starch coating
   • It denatures the protein, which tenderises the surface and helps it take up flavour
   • It hydrolyses the protein into sugars, which makes the meat taste sweet and syrupy once it is cooked

4. Approximately what temperature does egg white begin to set when heated gently?

   • About 100°C
   • About 180°C
   • About 60°C
   • About 15°C

5. Which cooking method is the clearest example of protein coagulation?

   • Rubbing cold fat into flour to make a crumb texture for a crumble
   • Poaching an egg in simmering water until the white turns firm and opaque
   • Sieving flour to remove lumps before it is weighed out for a cake
   • Dissolving sugar in hot water to make a clear sugar syrup

6. A chicken breast is cooked through to 75°C. What has happened to most of its protein?

   • It has gelatinised and trapped water in starch, so the juices thicken
   • It has denatured and coagulated, so the meat becomes firm and opaque
   • It has hydrolysed into sugars, so the meat turns sweet and golden brown
   • It has emulsified with fat, so the juices separate into a stable layer

7. An egg custard is baked too hot and turns grainy and watery. What has most likely happened?

   • The fat separated from the custard and pooled on the surface
   • The sugar caramelised on the base and turned the custard bitter
   • The proteins coagulated too quickly and squeezed out liquid as they tightened
   • The starch gelatinised too fast, making the custard gluey and heavy

8. Which change to protein helps a cooked meatball hold its shape?

   • Its sugar dissolves and draws water into the mince as it cooks
   • Its starch swells and glues the mince into a stiff paste
   • Its fat melts and caramelises around the outside of each meatball as it cooks in the oven
   • Its protein coagulates into a network that binds the mince together

9. Which factor denatures protein in a cooking context?

   • Adding lemon juice or vinegar to the food
   • Leaving bread dough to rest in a cool place
   • Adding caster sugar to a fruit compote
   • Rubbing cold butter into flour for pastry

10. Which of these is a sign that egg proteins in a quiche have coagulated fully?

    • The surface is glossy with a thin layer of liquid fat
    • The filling tastes sweet and has a caramelised top layer
    • The filling is set and holds a clean slice when cut
    • The filling is runny and pours away when the tin is tilted

11. What happens to the amino acids in a protein during denaturation?

    • They are split apart and released as free sugars into the cooking liquid
    • They dissolve into the fat and are removed when the food is drained
    • They are replaced by starch molecules taken from the flour in the mixture during baking
    • They stay joined in the same chain, but the chain folds into a different shape

12. Which temperature range is most associated with egg yolk setting?

    • About 65°C to 70°C
    • About 120°C to 130°C
    • About 40°C to 45°C
    • About 20°C to 25°C

13. A cook heats milk with beaten egg to make a sauce that must not curdle. Which action is most sensible?

    • Bring the mixture to a fast boil so the egg sets quickly and firmly
    • Add cold water to the mixture at boiling point to stop it from setting and make it smooth again
    • Leave the pan on high heat, uncovered, and do not stir for ten minutes
    • Heat gently and stir constantly so the egg sets smoothly without curdling

14. Which statement about protein denaturation is correct?

    • It makes proteins larger and heavier by adding water to the chain
    • It is the same process as the gelatinisation of starch in sauces
    • It only happens when food is frozen to below -18°C for long periods of storage in a home freezer
    • It can be caused by heat, acid or mechanical action such as whisking

15. Which fish texture change is typical when fillets are cooked in a hot pan?

    • The flesh turns brown and crisp as its sugars caramelise on the skin
    • The flesh turns opaque and flakes apart as its proteins coagulate
    • The flesh turns creamy as its fat emulsifies with the water it contains
    • The flesh turns clear and syrupy as its starch dissolves in the juices

16. What is the difference between denaturation and coagulation?

    • Denaturation is the unfolding of protein; coagulation is denatured proteins joining to set
    • Denaturation turns starch into dextrins; coagulation turns starch into sugars
    • Denaturation happens only in cold food; coagulation happens only in hot food
    • Denaturation is the joining of proteins; coagulation is the unfolding of protein

17. Why does a coagulated protein network usually not return to its original state after cooking?

    • The starch has swollen around the protein and locked the structure in place
    • The denatured molecules have bonded into a network that does not easily unfold back
    • The protein has been broken into amino acids that cannot re-form a chain
    • A coat of fat around each protein molecule stops the structure ever unfolding

18. A cook heats egg white only to 40°C and then cools it. What will the white be like?

    • Browned on the surface, because the sugars in the white have caramelised
    • Firmly set, because the protein has already coagulated fully and cannot change any further at this heat
    • Still runny, because denaturation and coagulation have not yet taken place
    • Thick and smooth, because the starch in the white has gelatinised

19. Which two changes accompany the protein denaturation in a cooked egg?

    • The clear white becomes opaque and the mixture becomes firm
    • The mixture becomes more liquid and the colour turns golden brown
    • The white becomes glossy and the yolk becomes emulsified with fat
    • The yolk turns sweet and the white becomes starchy and thick

20. Why does acid alone change the texture of raw fish in some dishes without heat?

    • Citrus juice gelatinises the fish fat, so the flesh becomes soft and moist
    • Citrus oils emulsify into the flesh, so the texture becomes creamy and smooth
    • Acid denatures and coagulates the fish protein, so it turns opaque and firm
    • Citrus sugars caramelise on the flesh, so the outside becomes brown and set

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