Potato starch grains (pink)

The pink oval structures are potato starch grains. One of the easiest and fastest way to observe starch grains is to scratch some sample off the surface of a potato with a sharp object and then adding some diluted iodine solution.

Further Reading

• Starch grains of a Potato

Method:

1. Cut the potato in half and scrape a little of the potato onto the microscope glass slide. This can be done either with a knife or with the fingernails. There should not be any large potato pieces on the glass.
2. Place a small drop of water on the “potato juice” and then place the glass cover slip on top.
3. Observe using the microscope. The starch grains will be visible as oval structures.
4. Now dilute a small amount of iodine in some water. The water should only turn slightly yellow. Place a drop of the dilute iodine next to the glass cover glass, so that some of the solution is able to flow between the cover glass and the slide.
5. You should be able to see how the starch grains change color. The iodine will react with the starch and turn it blue-black.
6. Alternatively, you can observe the starch grains in dark field or in polarized light (without adding iodine): Darkfield Microscopy | Simple Polarization Microscopy | Potato Starch Grains

Potato starch grains in dark field

Potato starch grains in bright field.

Here I would like to show you two images of potato starch grains taken with different optical contrasting methods. The top image was taken in dark field, the bottom one in bright field. The purple or red structures are the starch grains of the potato (Solanum tuberosum). This is a nice example on how the addition of a simple field-stop filter can result in drastically different images. The contrast of the images was adjusted and both images were sharpened slightly. Image stacking was not necessary. The starch grains of potatoes are also called amyloplasts, they are found inside the cells of the potato tuber. Starch is a polysaccaride, made of long chains of glucose molecules. The glucose was originally produced by the leaves of the potato plant. Starch can be present in the form of either amylose or amylopectin. It is not water soluble and therefore suitable for storage.