Food tests

Question 1

Give examples of reducing sugars

Answer 1

All monosaccharides e.g. glucose

Some disaccharides e.g. maltose and lactose

Question 2

Examples of non-reducing sugars

Answer 2

no monosaccharide

some disaccharides e.g. sucrose

Question 3

How do you carry out a test to test reducing sugars

Answer 3

Benedict’s test:

1. Add benedict’s reagent to food sample
2. heat using water bath
3. If it is positive colour change=green/yellow/orange/red precipitate

Question 4

Non-reducing sugars test

Answer 4

Benedict’s:

1. Add equal volume of HCL to hydrolyse the sugar
2. Heat in water bath
3. Carry out normal benedict’s test
4. if non-reducing sugar present colour change= green/yellow/orange / red precipitate

Question 5

How do you determine a glucose concentration of a solution

Answer 5

1. Produce a dilution series of glucose solutions of known concentrations
2. Perform Benedict’s test on each sample and remove the precipitate e.g. by centrifuge
3. Using colorimeter measure the absorbance to establish calibration curve
4. repeat with unknown sample and compare the absorbance to calibration curve.

Question 6

Test for starch

Answer 6

1. add iodine dissolved in potassium iodide to solution and shake
2. Blue black= starch present

Question 7

Test for lipids

Answer 7

Emulsion test

1. Add ethanol and shake
2. add water
3. Milky/cloudy white emulsion if present

Question 8

Test for proteins

Answer 8

Biuret test for proteins

1. Add biuret solution (sodium hydroxide+ copper ll sulphate)
2. Shake
3. protein present if purple colour present (if no present=stay blue)