Seliwanoff’s test definition
The Seliwanoff’s test is employed to differentiate between carbohydrates containing an aldehyde group and those containing a ketone group (ketose) (aldoses). This test employs a timed colour reaction peculiar to ketohexoses.
Objectives of Seliwanoff’s test
- to evaluate whether or not a sample contains ketohexoses.
- to separate aldoses from ketoses.
Principle of Seliwanoff’s Test
- Concentrated HCl and resorcinol constitute the test’s reagents.
- By hydrolyzing polysaccharides and oligosaccharides with acid, simpler sugars are produced.
- Aldoses dehydrate more slowly than ketoses do.
- Ketoses dehydrate in the presence of concentrated acid to create 5-hydroxymethyl furfural.
- During a series of condensation reactions, dehydrated ketose reacts with two equivalents of resorcinol to form xanthenoid, a complex (not a precipitate) exhibiting a deep cherry red colour.
- When the test is prolonged, aldoses may have a faint pink to cherry red hue upon reaction.
- The product and response time of the oxidation process make it simpler to differentiate various carbohydrates.
- Due to the fact that sucrose and inulin are digested by acid to produce fructose, these other carbs also produce a favourable outcome for this test.
Requirements
Reagent
- Add 0.05 percent resorcinol (m-hydroxybenzene) to 3 N HCl to get Seliwanoff’s reagent.
- Combine 100 ml of water with 33 ml of concentrated HCl after dissolving 50 mg of resorcinol in it.
- Test sample
- Distilled water
Materials required
- Test tubes
- Test tube stand
- Pipettes
Equipment
- Water bath
Procedure of Seliwanoff’s Test
- Fill one test tube with the test sample and another with distilled water to operate as the blank.
- 2 ml of Seliwanoff’s reagent should be added to each test tube.
- Keep both test tubes submerged in water for one minute.
- Take notice of the colour formation as you watch it happen.
Result and Interpretation of Seliwanoff’s Test
- The formation of the cherry-red complex is an indication of effectiveness, demonstrating that the submitted sample contains ketoses.
- A negative outcome, or one where the colour does not emerge at all or rather follows a considerable amount of time, indicates that the material under examination does not contain ketoses.
Uses of Seliwanoff’s test
- Seliwanoff’s colour reaction is utilised in the colorimetric measurement of fructose in fermentation medium.
- The concentration of ketoses in a particular sample can be determined using a modified version of this technique.
Limitations of Seliwanoff’s test
- High levels of glucose or other sugars may cause Seliwanoff’s reagent to produce similar-colored molecules, which might cause interference.
- Through the catalytic action of acid, prolonged boiling can convert glucose to fructose, causing the production of cherry red complex and hence a false-positive test outcome.
- A different test is needed to identify the specific ketose sugar because this test is generic and cannot discriminate between different types of ketoses.
References and Sources
- Tiwari A. (2015). Practical Biochemistry. LAP Lambert Academic Publishing.
- Sánchez-Viesca, Francisco & Gómez, Reina. (2018). Reactivities Involved in the Seliwanoff Reaction. 10.11648/j.mc.20180601.11.
- 4% – https://en.wikipedia.org/wiki/Seliwanoff%27s_test
- 3% – https://www.researchgate.net/publication/313745155_Practical_Biochemistry_A_Student_Companion
- 2% – https://www.youtube.com/watch?v=vOWoWxEdy0I
- 2% – https://diabetestalk.net/blood-sugar/chemical-test-to-distinguish-between-glucose-and-fructose
- 2% – https://biokamikazi.files.wordpress.com/2013/10/merged_document.pdf
- 1% – https://www.oxfordreference.com/view/10.1093/oi/authority.20110803100453548
- 1% – https://generalchemistrylab.blogspot.com/2011/12/seliwanoffs-test.html
- 1% – http://en.edubio.info/2017/02/seliwanoffs-test-for-ketose-sugars.html
