Starch Agar ( Hydrolysis test)

Brief protocol of Starch Hydrolysis

Day 1:

1. Obtain a Starch agar plate, label, divide into 2 sides ( E.coli & B.subtilis)

2. Sterilize inoculate loop

3. Aseptically transfer each organism to the side

4. Incubate for at least 24hours at 37°

Day 2:

• Add iodine dropwise from the center till cover all surface

• Observe the clearing. Record results

What is starch made of?

glucose subunits

In a mixture of starch, which form dominant?

Amylopectin

What is amylopectin?

Branched starch

What is amylose?

Linear starch

Which kind of enzyme used in starch hydrolysis? Why?

Exoenzyme

Because starch is too big to pass through the membrane, enzymes must be break down starches around the bacteria

What are the products of starch hydrolysis?

• Glucose

• Maltose

Which enzyme breaks down linear polysaccharides?

Amylase

Which enzyme breaks down branched polysaccharides?

Oligo-1,6-glucosidase

What is the substrate in Starch plate?

starch

What is tested for in Starch Agar?

Organisms that possess the enzymes to hydrolyze starch to use

Why is there a clearing around the growth of colony in Starch plate?

Because the enzymes catalyze starch around the bacteria

What is the indicator in Starch Agar?

iodine

reacts with starch → dark brown color, visualize the clearing around growth

What is the positive result of Starch Hydrolysis?

Clearing around growth with iodine indicator (no brown discoloration around growth)

→ Presence of either alpha-amylase or oligo-1,6-glucosidase

What is the negative result of Starch Hydrolysis?

No clearing or brown discoloration with iodine addition 

→ No presence of neither alpha-amylase or oligo-1,6-glucosidase