4: Chemical Food Tests

Question 1

Test for starch

Answer 1

Iodine

Question 2

test for starch method (2p)

Answer 2

• Crush the food sample if it’s solid
• Add a few drops of iodine

Question 3

Colour is starch present

Answer 3

blue/black

Question 4

Colour if starch isn’t present

Answer 4

brown/orange

Question 5

Iodine risk assessment (2p)

Answer 5

– iodine is an irritant
wear safety goggles and avoid contact with skin/eyes

Question 6

Possible sources of error (2p)

Answer 6

• colour is subjective
• possible cross-contamination

Question 7

Test for sugars

Answer 7

Benedicts solution

Question 8

Test for sugars method (2p)

Answer 8

• Add benedicts solution and the crushed food to a boiling tube
• Heat in a water bath

Question 9

colour if sugar present (2p)

Answer 9

• red to green
• red is the strongest and green the weakest

Question 10

colour if sugar not present

Answer 10

blue

Question 11

Test for protein

Answer 11

biuret solution

Question 12

test for protein method (3p)

Answer 12

• add food sample to test tube
• add biuret regent and mix
• place white card behind the test tube to make the colour more visible

Question 13

Biuret risk assessment

Answer 13

• it is corrosive and an irritant
• wear goggles and avoid contact with skin

Question 14

colour if protein present

Answer 14

purple

Question 15

colour if protein not present

Answer 15

blue

Question 16

Tests for lipids (2p)

Answer 16

Sudan III and ethanol

Question 17

Test for lipids using Sudan III method (2p)

Answer 17

• the food and water are added to a test tube
• drops of Sudan III are added to the test tube and it is shaken

Question 18

Test for lipids using ethanol (2p)

Answer 18

• ethanol is added to crushed food in a test tube
• the liquid is poured into a separate test tube containing water, leaving any food residue behind

Question 19

Sudan III and ethanol hazard (2p)

Answer 19

• they are both flammable
• wear safety goggles and avoid contact with skin or eyes

Question 20

colour if lipids present Sudan III

Answer 20

red layer

Question 21

colour of lipids not present in Sudan III

Answer 21

pink

Question 22

colour if lipid present in ethanol

Answer 22

emulsified/cloudy

Question 23

colour if lipid not present in ethanol

Answer 23

not emulsified

Question 24

How lipids in food samples can be measured (when using ethanol-emulsion) (2p)

Answer 24

• Could measure how much light can get through the sample
• The less light the more lipid

Question 25

How to avoid cross-contamination

Answer 25

Use a different pipette for each sample and don't reuse them