I am doing starch-iodine assay for measure the enzyme activity. I use starch as substrate. I add the soluble starch to the form of a paste and slowly add it into the hot water. When I start measuring process, starch concentration starts to decrease over time and this happens in a very short time. What should I do to keep the starch concentration the same?
When starch & water are subjected to heat (within temperature range 51- 78 oC depending on source...corn, rice, etc) , the starch will swell and the process is called gelatinization. The heat causes breakdown of starch first into dextrins and eventually to glucose.
Please do not reveal you research to me. However, I wonder if you can avoid adding the paste "or gelatinized starch" to "hot" water -as you said- and to try "cold" water if possible.
Dear Leyla Yılmaz,
Solving starch in hot water or heating the water cause starch gelatinization in which the intermolecular bonds of starch molecules break down and allow the hydrogen bonding sites to engage more water.
The optimum temperature of water for solving starch is 4-5˚C. The optimum time depends on the size and concentration of starch. It is better to mix the solution during adding water to the starch. The starch solution concentration which it disolves competely is (10 mg/ml).
Also check https://www.exilva.com/blog/a-way-to-reach-prolonged-stability-of-starch-adhesives?hs_amp=true
Dear Nizar Matar ,
Thank you for your answer. I mean hot water about 90 degrees (not boiling).
When I try it in cold water, there is no clear view. The color of the solution turns white. Doesn't that mean starch is insoluble?
Dear Mina Karimi-Avargani ,
Thank you for your answer. When I try it in cold water, there is no clear view. The color of the solution turns white. Doesn't that mean starch is insoluble?
Yes, starch as a whole is insoluble in cold water & only the amylose part of it is water-soluble.
Anyhow, please see this article which discusses how starch solution is made:
https://www.techknow.org.uk/wiki/index.php?title=Making_up_starch_solution#:~:text=In%20general%2C%20starch%20is%20insoluble,then%20dissolved%20in%20boiling%20water.
- Badges
- Science topic
- Similar topics
- Biological Science
- Molecular Biology
- Molecular Methods
- Cloning