BIOCHEM: CARBOHYDRATES (PART 2)

All reducing sugars must have a _________.

free aldehyde/ketone group

All _____ and _______ reduce oxidizing agents except ______.

1.) monosaccharides
2.) Disaccharides
3.) Sucrose

What are the oxidizing agents used in carbohydrate test part 2?

1.) Cupric ion
2.) Dinitro salicylic acid
3.) Picric acid
4.) Silver Ions

Test that is very sensitive under mildly alkaline conditions. 

Benedict’s Test

Copper (II) to Copper (I) means Cu²⁺ ions in Benedict’s solution are __________, forming a ___ precipitate when a reducing sugar is present.

1.) reduced to Cu⁺ ions
2.) red

What are benedict’s reagents?

1.) CuSO₄ (Copper II sulfate)
2.) Na₂CO₃ (Sodium carbonate)
3.) Na₃C₆H₅O₇ (Sodium citrate)

Color of Cu²⁺ ions in Benedict’s Test

Blue

Color of Cu⁺ ions in Benedict’s Test

Brick red

Indicator of positive result in Benedict’s Test

Brick red precipitate

What is the reducing substance/positive compounds in Benedict’s Test?

1.) Mostly aldehyde
2.) Phenylhydrazine
3.) Hydrazo benzene
4.) Formic acid 
5.) Phenols 
6.) Uric acid 
7.) Pyrogallol

Measurment of juice in Benedict’s Test

1mL

Sugar used in Benedict’s test

3% Sucrose

Measurement of Benedict’s reagent used

3mL

Minutes of boiling in Benedict’s Test

2-3 min

Benedict’s Test Result: 

1.) Juice

Result: Yellow precipitate (positive)

Benedict’s Test Result:

1.) 3% Sucrose

Result: Blue (negative)

Why is 3% sucrose tested negative for Benedict’s Test?

The anomeric carbons of glucose are joined together by a glycosidic bond, which locks the reactive group so they can’t reduce the copper II ions in Benedict’s reagent. (No free reducing group) 

Reagent used for Tollen’s Test

Ammoniacal solution of silver

Tollen’s Test, test for presence of?

Aldehyde

Appearance of a positive Tollen’s test

gray-black (silver mirror)

How many drops of sugar was used in Tollen’s Test?

5 drops

Measurement of Tollens reagent

2mL

Boiling time of Tollens Test

5 min

Chemical reaction of Tollens Test

Chemical symbol of silver

Ag

Sugars used in Tollen’s Test

1.) 3% Fructose
2.) 3% Sucrose 
3.) 3% Glucose

Tollen’s Test results

Fructose and glucose are positive except sucrose.

Why sucrose is negative? in Tollen’s Test?

Because is a non reducing sugar. It’s anomeric carbons are tied up by glycosidic bonds which locks the reactive group.

Tollen’s Test Final color change interpretation:

1.) No color change (blue)

No reducing sugars present

Tollen’s Test Final color change interpretation:

1.) Green

Trace amounts of reducing sugars present

Tollen’s Test Final color change interpretation:

1.) Yellow

Low amounts of reducing sugars present

Tollen’s Test Final color change interpretation:

1.) Orange

Moderate amounts of reducing sugars present

Tollen’s Test Final color change interpretation:

1.) Brick-red

Large amounts of reducing sugars present

Will disaccharides and polysaccharides give positive result for Molisch Test?

Yes all carbohydrates and polysaccharides give positive result for Molish test because they all form furfural derivatives in the presence of acid 

Which of different carbohydrate test would give a positive result for maltose? Describe color change

Maltose gives positive results in Benedict’s, Fehling’s, and Tollens’ tests, showing brick-red or silver mirror color changes — all indicating it is a reducing sugar.

Can Seliwanoff’s test be used to distinguish between fructose?

Yes, Seliwanoff’s test react faster with ketoses like fructose, producing a cherry red color.

Inulin is a polysaccharide composed of fructose units. Which test should be used to identify the presence of fructose?

The Seliwanoff’s test can identify fructose since it’s specific for ketose sugars.

What is the purpose of Bial’s orcinol test? What chemical reaction occurs between Bial’s orcinol reagent  and sugars (pentose and hexose), and what colored products are formed when the sugar is pentose or a hexose?

Bial’s orcinol test detects pentoses by converting them into furfural, which reacts with orcinol and ferric ions to produce a blue-green color.
Hexoses form hydroxymethylfurfural, giving a yellow-brown color instead.

What is the purpose of Barfoed’s test, what is the composition of the Barfoed’s reagent, and what indicates a positive result in this test?

Barfoed’s Test uses Cu(CH₃COO)₂ in acetic acid to detect reducing sugars.
A brick-red precipitate of Cu₂O indicates a positive result, appearing quickly for monosaccharides and slowly for disaccharides.