Explain why two of the carbohydrates failed to give positive tests. (The reasons

Question

Explain why two of the carbohydrates failed to give positive tests. (The reasons for the failure are different for the two carbohydrates.) Hydrolysis of Disaccharides and Polysaccharides What was the color of the initial iodine test on the starch solution? After the starch solution was heated in the water bath for 10 minutes, did the iodine test indicate that hydrolysis has occurred? Did the Fehling test confirm this? Give the evidence for both of your answers. Did Fehling's test indicate that hydrolysis of sucrose has occurred after 10 minutes? What is your evidence? Give the names of the products that were formed upon hydrolysis of sucrose and starch. Sucrose: Starch: The Molisch Test: A General Carbohydrate Test Give the name of each carbohydrate and the exact color obtained for each in the test. What type of reaction occurs with each carbohydrate in the Molisch test? What organic product is formed? Is the same organic product formed for each carbohydrate? Explain on the basis of your observations. Draw a segment of the structure of a typical molecule of the carbohydrate in flour. Test for Starch in Food Products Which of the food products gave a positive test for starch?

Explanation / Answer

Hydrolysis of Disaccharides and polysaccharides:

Solution,

The answers have to be based on the experimental observation of the analyst. But I have tried to explain normal trend or common observation for a positive result experiment.

2. If starch is totally has been hydrolyzed there should not be blue –black coloration after iodine test. After hydrolysis starch breaks into smaller molecules like glucose, etc. If it is formed then Fehlings test should show positive result. That is addition of Fehlings solution should give change of color to orange.

3. Depending upon the starting solution prepared of sucrose and type of reagent and hydrolysis used for experiment, if sucrose hydrolysis has occurred then colour change of solution to orange after Fehlings test, is the evidence for it.

4. Products after hydrolysis:

Depending upon the enzyme used for starch hydrolysis experiment , the products vary. I have noted list of common enzymes and respective products.

Starch:

a) Use of -Amylase as enzyme à Disaccharide maltose and Trisaccharide maltotriose

b) -Amylase as enzyme à Disaccharide maltose

c) -Amylase as enzyme à Glucose

Sucrose:

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