I did qualitative assay on agar plates with starch as sole carbon source for checking amylase activity, once I added iodine the clear zone appeared arround the colonies but after some hours and for the next few days the clear zone dissappeared and the plate colour was blue, so why the clear zone dissappeared and what is the correst time to get proper results immediately after pouring iodine or I should wait till next day??
Because of the ongoing enzymatic activity of amylase, which breaks down the starch surrounding the colonies, the clear zone on agar plates that indicates amylase activity gradually fades. Iodine first combines with starch to form a blue-black complex, with the exception of regions where amylase has broken down the starch, leaving a clear zone. But ultimately, the clear zone vanishes and the entire plate turns blue-black as amylase keeps breaking down the starch.
After adding iodine, you should observe the plates at certain intervals to obtain the most precise findings. The ideal way to find the appropriate time to observe the clear zone is to start monitoring the plates as soon as you add iodine and then at regular intervals (e.g., every hour). This can vary depending on the activity of amylase in your samples. If you wait until the following day, the iodine-starch complex's blue-black coloring can cover over the clear zone.
Saif Saad Turki if amylase keeps breaking down the starch, how the clear zone fades and turns blue black again which is indicating that starch is not broken?
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