3.3.2.4 Enzymic browning and oxidation in fruit and vegetables Quiz: AQA Food Preparation and Nutrition, Unit 2

The 20 questions

1. What is enzymic browning in cut fruit?

   • Starch in the fruit gelatinises and turns the cut surface a brown colour
   • Sugars in the fruit heat up and caramelise into a dark brown syrup
   • Proteins in the fruit denature and set into a brown coating on the flesh
   • Enzymes react with oxygen once cells are damaged, producing brown pigments on the flesh

2. Why is lemon juice squeezed over sliced apples?

   • The acid denatures the apple fat so that it cannot oxidise
   • The acid slows the enzyme action that causes browning
   • The acid gelatinises the apple starch into a protective film
   • The acid caramelises the apple sugars and seals the surface

3. What is oxidation in fruit and vegetables?

   • Melting of fat in vegetables during gentle heating in a pan
   • Setting of plant protein into a firm gel during steaming for a short time in the pan
   • Loss of water-soluble vitamins such as vitamin C when food is exposed to air
   • Gain of water-soluble vitamins from the cooking water during boiling

4. Why are vegetables best cut shortly before they are cooked?

   • Cut surfaces set protein, so the vegetables turn firm and opaque as they wait
   • Cut surfaces expose more area to oxygen, which speeds vitamin loss and browning
   • Cut surfaces trap more water, which thickens the vegetables and softens them
   • Cut surfaces dissolve more fat, which makes the vegetables greasy to the touch and slippery in the pan

5. Which vitamin is most easily lost by oxidation during the preparation of vegetables?

   • Vitamin K
   • Vitamin A
   • Vitamin C
   • Vitamin D

6. Which method most reduces water-soluble vitamin loss when cooking vegetables?

   • Boiling them in a large volume of water for thirty minutes or more
   • Cutting them into very small pieces and leaving them to stand exposed
   • Cooking them quickly in a small amount of water or steaming them
   • Soaking them in cold water for several hours before they are cooked

7. A cook wants to stop avocado browning before serving a dip. Which action is most effective?

   • Whisking the flesh with cream to emulsify the surface of the dip
   • Heating the flesh in a pan until it caramelises on the surface
   • Squeezing lemon or lime juice over the flesh and covering it closely
   • Leaving the flesh uncovered in a warm room for several hours overnight

8. Why is washing vegetables quickly better than soaking them for a long time?

   • Long soaking gelatinises the starch and makes the vegetables gluey
   • Long soaking caramelises the vegetable sugars so they taste bitter
   • Long soaking emulsifies the fat in the skin into the water
   • Long soaking lets water-soluble vitamins leach out into the water

9. A cook steams broccoli rather than boiling it. Why does this keep more vitamin C?

   • Steam caramelises the vitamin, locking it into the florets of the broccoli
   • Less vitamin C leaches into cooking water and less is exposed to oxygen
   • Steam gelatinises the vitamin, trapping it inside a starch coating
   • Steam emulsifies the vitamin with the natural fats in the broccoli

10. Why should cooking water from vegetables be reused in a soup or sauce?

    • It contains sugar that caramelises into a rich, brown flavour
    • It contains water-soluble vitamins and minerals that leached out during cooking
    • It contains fat that emulsifies with the vegetables to make a sauce
    • It contains starch that gelatinises to thicken the soup slightly

11. Mashed potato left exposed turns grey. Which chemical process is most likely?

    • Dextrinisation, caused by dry heat browning the starch on the surface
    • Emulsification of the milk and fat in the potato as it cools
    • Coagulation of the milk protein in the mash as it stands at room temperature for a while
    • Enzymic browning, caused by enzymes reacting with oxygen in the damaged potato

12. Why does acid help preserve the colour of cut fruit?

    • Acid raises the pH, which makes fruit pigments darker and more stable over the day
    • Acid dries the surface, so the fruit cannot caramelise and turn brown
    • Acid lowers the pH, which reduces the enzyme activity that causes browning
    • Acid dissolves oxygen, so the fruit has no oxygen left to react with

13. Which preparation step is most likely to lead to enzymic browning?

    • Peeling and slicing apples and leaving them uncovered on a board
    • Sealing whole, unpeeled melons in a cool fridge overnight
    • Roasting whole, unpeeled potatoes in a dry oven at a high heat
    • Dicing firm carrots and storing them in a sealed bag in the fridge

14. Which technique is used to remove the skin from tomatoes before further preparation?

    • Scoring the skin and plunging the tomatoes briefly into boiling water
    • Soaking the tomatoes overnight in cold, salted water to loosen the skin
    • Freezing the tomatoes whole and then steaming them to soften the skin
    • Grating the tomatoes while raw and leaving them to ripen in a bowl

15. What is the main reason for cutting vegetables into uniform pieces?

    • So that their enzymes are destroyed at the same moment
    • So that they cook evenly and at the same rate
    • So that their vitamin content is fully preserved during the cooking
    • So that they caramelise on all sides at the same time

16. Why are vegetables blanched before freezing rather than frozen raw?

    • To destroy enzymes that would otherwise cause loss of colour, flavour and texture in the freezer
    • To caramelise the sugars so they stay sweet and keep their colour through the freezing period
    • To gelatinise the starch so the vegetables freeze together into a solid block for easy storage
    • To emulsify the water so that only very small ice crystals form inside the cells of the food

17. Which statement about the oxidation of water-soluble vitamins is correct?

    • Losses decrease with longer soaking, because the vitamins are stored in the water
    • Losses increase with longer cutting-to-cooking times, higher heat and more water
    • Losses are fully prevented by sealing vegetables in a tin before cooking
    • Losses are unaffected by cooking, because vitamins are fat-soluble

18. Which two factors most promote enzymic browning in cut fruit?

    • Exposure to cold water and a high starch content in the flesh
    • Exposure to light and a high sugar content in the flesh
    • Exposure to fat and a high protein content in the flesh
    • Exposure to oxygen and enzyme activity in the damaged flesh

19. Sliced peppers left in a bowl lose vitamin C. Which cause is most likely?

    • Starch in the peppers gelatinising in the cold water of the bowl
    • Vitamin C reacting with oxygen as the cut surfaces are exposed to air
    • Fat in the peppers emulsifying with the juices and separating
    • Sugar in the peppers caramelising under the heat of the kitchen light

20. Why does cold storage slow the browning of a cut apple?

    • Cold gelatinises the apple starch into a protective skin over the flesh
    • Cold speeds up caramelisation of the apple sugars and darkens them
    • Cold slows enzyme activity, so browning happens more slowly
    • Cold denatures the apple protein and sets it firm over the cut surface

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