Iodine staining to determine the ripeness of a fruit

Today, we had learnt about the iodine staining or iodine test that being used to test the presence of starch.

As the fruit becomes ripen, the burst ethylene production will activate the enzymes such as kinases, amylases, and hydrolases

Basically, the starch is present or have slightly higher content while unripen
when the fruit is ripen, the ethylene initiates the metabolic pathway of the conversion of the starch to sugar (glucose or sucrose)

During iodine test, the fruits that have been stained and turned blue/dark blue color shows the presence of starch
(Iodine is very sensitive to the presence of starch)

However, the results are not pretty convincing
the iodine solution should be at the right concentration

besides that, different varieties of the fruits may affect the result
This is due to varied genotypes present in each varieties

That's all

Have a nice day ^^

Fruit samples for iodine test

left: unripen papaya; right: semi-ripen 

left: ripen banana; right: unripen banana

left: sweet potato; right: radish

Cross section of radish that has been stained with iodine solution

Unripen papaya shows no changes to the surface after being stained.

Sweet potato contains a lot of starch; positive result

No changes

The unripen banana has intense color of blue stain

Comparison between ripen and unripen banana


Staining procedure (stain for 1 min)
Note: Sweet potato is known as storage organ
it contains rich starch content

the sugar (glucose or sucrose; simplest sugar) is used for immediate-use

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