KA8: P6 Chemical food test

Question 1

What are the 4 chemical food tests?

Answer 1

1. Starch
2. Protein
3. Fat & oil
4. sugar

Question 2

Test for starch

Answer 2

Iodine solution test

Question 3

Test for protein

Answer 3

Biuret test

Question 4

Test for Fat & Oil (lipids)

Answer 4

Ethanol Emulsion test

Question 5

Test for sugars (reducing sugars)

Answer 5

Benedict’s solution test

Question 6

What is lipids

Answer 6

Fat & Oil

Question 7

Starch test - how

Answer 7

1. add drops of iodine solution to the food/test sample
   -ve: color stays same
   +ve: color changes blue-black

Question 8

+ve starch

Answer 8

If starch present:
color changes to blue-black

Question 9

-ve starch

Answer 9

No starch present:
colour remains browny-orange

Question 10

Protein test - how

Answer 10

1. add a few drops of potassium hydroxide solution to make solution alkaline
2. add some copper sulfate solution
   OR just add some biuret solution
   -ve: solution stays blue
   +ve: solution turns purple

Question 11

-ve protein

Answer 11

no protein:
solution stays blue

Question 12

+ve protein

Answer 12

protein present:
solution changes to purple

Question 13

What is a biuret

Answer 13

mixture of potassium hydroxide and copper sulfate solutions

Question 14

Fat/Oil test - how

Answer 14

1. Mix sample with ethanol (2ml) and is shaken until it dissolves
2. Pour solution in (cold) water (equal vol)
   -ve: colorless
   +ve: if lipids are present, they’ll precipitate out of the liquid and milky/cloudy emulsion on top (more fat=more milky)

Question 15

Emulsion

Answer 15

When one liquid doesn’t dissolve in another - forms little droplets

Question 16

-ve lipid

Answer 16

is colorless

Question 17

+ve lipid

Answer 17

Cloudy/milky (white) emulsion formed

Question 18

Sugar test - how

Answer 18

1. Add (2ml) Benedict’s solution (blue) to the samples and heat in a water bath at 75C (heated/boiled) for 2-3 min
   -ve: No colour change if no sugar present
   +ve: forms a coloured precipitate (higher concentration of sugar = further the colour change goes

Question 19

reducing sugars

Answer 19

types of sugar molecules, due to their chemical properties
(act as a reducing reagent ) e.g. glucose
(not sucrose)

Question 20

color of precipitate changes from

Answer 20

Blue(none)–>Green(trace)–>Yellow(low)–>Orange(moderate)–> Brick red (high) concentration

Question 21

+Ve sugar

Answer 21

forms a colored precipitate
(higher concentration of sugar = further the color change goes)
(orange/brick-red - definitive result)

Question 22

-Ve sugar

Answer 22

No color change or precipitate formed

Question 23

Benedict’s solution

Answer 23

a chemical solution that changes color in the presence of glucose and other reducing sugars, used in clinical urine tests for diabetes. It is a mixture of sodium or potassium citrate, sodium carbonate, and copper sulphate.

Question 24

Why might theses test not be the best

Answer 24

They are all qualitative tests and are very subjective depending on how people see them.
(except for the benedict’s test - semi-quantitative)

Question 25

basics
the 7 food groups

Answer 25

1. carbohydrates(sugar + starch)
2. fats & oils
3. proteins (form amino acids)
4. fibre
5. vitamin
6. mineral
7. water