Topic 1: Food tests

Question 1

Describe the tests for lipids.

Answer 1

-Emulsion test
-Add ethanol and shake, then add water.
-Positive results would show a milky white emulsion

Question 2

Describe the test for proteins

Answer 2

Add biuret reagent and shake
Negative results: Remains pale blue
Positive: Turns into a purple colour

Question 3

How would you test for starch?

Answer 3

Add iodine
Negative: Brown/orange
Positive: Blue-black

Question 4

What are the reducing sugars?

Answer 4

-Glucose
-Fructose
-Galactose
(All monosaccharides)
-Maltose
-Lactose
(Some disaccharides)

Question 5

What is the non-reducing sugar

Answer 5

Sucrose

Question 6

How can you test for reducing sugar?

Answer 6

-Add benedict’s solution (Blue)
-Heat in a boiling water bath
-Positive: Green-Little sugar to Red-A lot of sugar

Question 7

How can you test for a non-reducing sugar?

Answer 7

Do benedict’s test, and if it remains blue then do this:
-Add dilute HCL acid and heat in a boiling water bath
-Add an alkali to neutralise
-Add benedict’s reagent again and heat.

Question 8

Why do you add an acid when testing for non-reducing sugars?

Answer 8

To break the glycosidic bonds to produce monosaccharides.