mucic and barfoeds test

BARFOED’S TEST

Knowing who’s Lonely ;)

A biochemical test to detect monosaccharide

(reducing) sugars in solution

Disaccharides will also respond to the test

with prolonged heating and under proper

conditions of acidity leading to hydrolysis of

the disaccharides

NOTE:

: Sugars are less reactive in acid than

in alkaline media

: Disaccharides are less reactive than

monosaccharides

MONOSACCHARIDE

(from Greek monos: single, sacchar: sugar)

are the most basic units of biologically

important carbohydrates.

They are the simplest form of sugar and are

usually colorless,water-

soluble, crystalline solids

Some monosaccharides have a sweet taste

PROCEDURE

add 10 drops of solution to 3 ml Barfoed’s

Reagnet,

place in a boiling bath for 5 min

Remove and allow to cool

• Observe the results at once after 15

minutes of boiling.

• NOTE: To ensure correct reading inspect

carefully the presence of small amount of

brick red precipitate.

Negative result Positive Result

RESULTS

Barfoeds

Test

Test solutions (1% W/V)

Galactose Glucose Fructose Maltose Sucrose Xylose

:first 5

minutes

+ Low

precipitate

+ Low

precipitate

+low

precipitate

- No

precipiate

+low

precipitate

+ low

precipitate

:next

15

minutes

+High

precipitate

+High

precipitate

+High

precipitate

+High

precipitate

+High

precipitate

+High

precipitate

DISCUSSIONS

Barfoed's Test is a chemical test used for

detecting the presence of monosaccharides.

It is based on the reduction of copper(II)

acetate to copper(I) oxide (Cu2O), which

forms a brick-red precipitate

The Barfoed’s Test is a

chemical test carbohydrate that can be

used to identify the existence of

monosaccharides in the sample.

Heating the tubes beyond 10 minutes can

result in hydrolysis of disaccharides to

monosaccharides, thus producing a “false-

positive” reaction.

Barfoed's reagent consists of a

0.33 molar solution of neutral copper acetate

in 1% acetic acid solution.

The reagent does not keep well and it is

therefore advisable to make it up when it is

actually required.

RCHO +2Cu2+ → RCOOH +

4H+ +2H2O

+Cu2O↓

APPLICATION

Lactose Intolerance- Congenital disorder

consisting of an inability to digest milk and

milk products; absence or deficiency of

lactase results in an inability to hydrolyse

lactose

MUCIC TESTHear the sound of the Galactose

A test specifically useful in the identification

of GALACTOSE

Mucic acid is another name of galactaric

acid.

Mucic acid test is named for the product of

the reaction.

GALACTOSE

(from Greek γάλακτος galaktos "milk"),

sometimes abbreviated Gal

is a type of sugar that is

less sweet than glucose. It is considered a

nutritive sweetener because it has food

energy. It is a C-4 epimer of glucose.

Galactose is a monosaccharide. When

combined with glucose, through

a dehydration reaction, the result is

the disaccharide lactose.

Galactose and glucose are the

two monosaccharide sugar components that

make up the disaccharide sugar, lactose

THREE principal derivatives of Aldoses

Aldonic Acids(alcohol Acids)- the aldehyde is

oxidized

Uronic Acid- those in which the primary alcohol

group is oxidized

Saccharic acids- both the aldehyde and primary

alcohol groups are oxidized

PROCEDURE

Place 2ml of the test solution in a large test

tube

Add to 5ml of concentrated Nitric Acid

Place the tube in the boiling water bath for

one Hour

Scratch the inner wall of the tube with glass

rod

Let it stand for 30-45 min or overnight if no

crystals were formed.

Examine the crystals on the microscope

RESULTS

Test solutions (1% W/V)

Galactose Glucose Fructose Maltose Sucrose Xylose

Mucic

Test

Positive

-presence

of crystals

None None None None None

DISCUSSIONS

The aldehyde and primary alcohol groups

are oxidized to CARBOXYL groups in the

reaction of galactose with HNO3 forming

Saccharic Acid

The saccharic acid formed from the free or

combined glucose is insoluble and seperates

out as colourless crystals in the cold

HC=O-(CHOH)4-COOH (aq) + 2 HNO3 (aq)

------>

HOC=O-(CHOH)4-COOH (s) + H2O (l) + 2 NO2

OHCH2OH

O

OHOH

OH

HNO3

OHCOOH

OH

OHOH

COOH

APPLICATION

Galactose is a component of the antigens

present on blood cells that determine blood

type within the ABO blood group system

Determining Galactose present on urine

Galactosemia- A genetic in which an enzyme needed to metabolize galactose is deficient or absent; typically develops shortly after birth

A galactosemia test is a blood test (from the heel of the infant) or urine test that checks for three enzymes that are needed to change galactose sugar that is found in milk and milk products-into glucose, a sugar that your body uses for energy

A person with galactosemia doesn't have one

of these enzymes. This causes high levels of

galactose in the blood or urine.