Practical 7: Identification of biological molecules in Foods

Why do we use water as a control in biochemical tests?

Water does not contain biological molecules- its a negative control

How can you determine which food has the highest lipid content?

By performing the Sudan III test and observing the most intense orange stain.

Why does Biuret reagent react with proteins but not free amino acids?

It detects peptide bonds, which are absent in free amino acids.

Match: Potato

Starch

Match: Chicken soup

Peptide bonds

Match: Dates

Reducing sugars

Match: Coconut

Lipids

Enzymes are:

Proteins

When an enzyme is exposed to high temperature or pH, what happens?

It becomes denatured

testing for reducing sugars, add how much mL of ?

2mL of benedicts reagent

red/brown signifies?

Prescence of reducing sugars

green signifies?

Prescence of a small amount of reducing sugars

testing for starch, add how much drops of?

5 drops of concentrated iodine solution

blue/black signifies?

positive result

red/orange/yellow signifies?

negative result

testing for fat, add what on what using a pipette?

sudan III dye on filter paper

soak the filter paper for?

3 mins

Why have the lipid extracts been made in 95% ethanol?

because they are not soluble in water

testing for protein, add how much drops of?

2 drops of biuret's reagent

color changes from to?

from blue to violet because of the Cu2+ ions reacting with the protein peptide bonds