Results table

Food 1. Starch iodine test

2. Benedict´s test for reducing sugar

3. Biuret test for protein

4. Emulsion test for lipids

1.Egg white

2.Bread

3.Vegetable oil

4.Apple

5.Sweet

6.Milk

7.Sweet biscuit

8.Cheese

Luís Moreira

Chemical Food Testing

Aim

To identify if starch, sugar, protein and fat are present in 8 different types of food.

Introduction

Food tests enable you to find out what kind of food types a food contains.

FOOD TESTS:

FOOD TYPE TESTING REAGENT RESULT

STARCH Iodine solution+ = black

- = yellow/ brown

REDUCING SUGARe.g. glucose Benedict´s solution

+ = orange/ red

+/- = yellow/ green

- = blue

PROTEIN Biuret reagent+ = purple

- = blue

FATS Ethanol & water

+ = cloudy white

- = colourless

(+ = positive; +/- = slightly positive; - = negative)

Luís Moreira

2. Benedict´s test for reducing sugar e.g. glucose

Method

1. With a marker label 8 test tubes with numbers 1-82. Add 1 cm3 of food to each test tube3. Add 1 cm3 of distilled water 4. Add enough Benedict´s solution to cover the food & water.5. Place 4 test tubes in a beaker (x2) with water6. Place the beakers on a hot plate for about 3 minutes7.Observe the colour change and record your results on the results table – orange/red indicates presence of reducing sugar; yellow/ green concentration of reducing sugar low; blue no reducing sugar present

Diagram

Safety

HAZARD CONTROL MEASURES

Benedict´s solution Irritant Wear a lab coat & gogglesWash hands & skin if it spills

Burning Don´t touch hot plate & don´t put your head over it

Luís Moreira

Benedict´s solution

Hot plate

3. Biuret test for protein

Method

1. With a marker label 8 test tubes with numbers 1-82. Place 1 cm3 of food to each test tube3. Add 1 cm3 of distilled water4. Slowly, drip 1 cm3 of Biuret reagent5. Wait 3-5 minutes6. Observe the colour change and record your results on the results table – purple indicates presence of protein; blue no protein present

Diagram

Safety

HAZARD CONTROL MEASURES

Biuret solution Irritant Wear a lab coat & gogglesWash hands & skin if it spills

Luís Moreira

Biuret reagent

4. Emulsion test for lipids

Method

1. With a marker label 8 test tubes with numbers 1A-8A & other 8 test tubes with numbers 1B-8B2. Place 1 cm3 of food to each test tube labelled A3. Add 2 cm3 of ethanol4. Shake test tubes 1A-8A5. Pour 1 cm3 of liquid (not food) gently into test tubes labelled B 6. Add some distilled water & shake again7. Observe and record your results on the results table – cloudy white indicates presence of lipids; colourless no lipids present

Diagram

Test tubes B

Safety

HAZARD CONTROL MEASURESEthanol Flammable Irritant

Wear goggles

Luís Moreira

Ethanol

Distilled water

Test tubes A

Conclusion

Egg white - tested negative for starch, slightly positive for reducing sugar and positive for protein & lipids. Egg white has protein, lipids & a small amount of reducing sugar. It does not have starch.

Bread - tested negative for protein & lipids, slightly positive for reducing sugar and positive for starch. Bread has starch & a small amount of reducing sugar. It does not have protein & lipids.

Vegetable oil - tested negative for starch & protein, slightly positive for reducing sugar and positive for lipids. Vegetable oil has lipids & traces of reducing sugar. It does not have starch & protein.

Apple - tested negative for starch, protein & lipids and positive for reducing sugar. Apple has reducing sugar. It does not have starch, protein & lipids.

Sweet - tested negative for starch, protein & lipids and slightly positive for reducing sugar. Sweet has traces reducing sugar. It does not have starch, protein & lipids.

Milk - tested negative for starch, slightly positive for reducing sugar and positive for protein & lipids. Milk has protein, lipids & a small amount of reducing sugar. It does not have starch.

Sweet biscuit - tested negative for protein, slightly positive for reducing sugar & positive for starch & lipids. Sweet has starch, traces of reducing sugar & lipids. It does not have protein.

Cheese - tested negative for starch & for reducing sugar and positive for protein & lipids. Cheese has protein & lipids. It does not have starch & reducing sugar.

Luís Moreira

1. Starch iodine test

Method

1. Number 1-8 on a spotting tile2. Place a sample of each food in each spot3. Add 2 drops of iodine solution to each sample4. Observe the colour change and record the results on the results table – black indicates presence of starch; yellow/brown no starch present

Diagram

Luís Moreira

1 2 3 4

5 6 7 8

Iodine solution

Safety

HAZARD CONTROL MEASURES

Iodine solution Harmful

Wear a lab coat & gogglesWash hands & skin if it spills

Spotting tile