What are reducing sugars? Describe any one method for estimation of reducing sugars.
Answers
the substance that breakdown sugar is called reducing sugars
A reducing sugar is any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group. All monosaccharides are reducing sugars, along with some disaccharides, oligosaccharides, and polysaccharides. The monosaccharides can be divided into two groups: the aldoses, which have an aldehyde group, and the ketoses, which have a ketone group. Ketoses must first tautomerize to aldoses before they can act as reducing sugars. The common dietary monosaccharides galactose, glucose and fructose are all reducing sugars.
There are many methods by which we can determine the reducing sugar. Several colorimetric methods are phenol-sulfuric acid, anthrone-sulfuric acid, 3,5-dinitrosalicylic acid (DNS), potassium ferric hexacyanide reagent (Prussian blue), and the Nelson-Somogyi (molybdenum blue) methods. According to me the DNSA method is more suitable and easy for reducing sugar determination and widely accepted too.
DNSA METHOD :--
3,5-Dinitrosalicylic acid (DNSA, IUPAC name 2-hydroxy-3,5-dinitrobenzoic acid) is an aromatic compound that reacts with reducing sugars and other reducing molecules to form 3-amino-5-nitrosalicylic acid, which absorbs light strongly at 540 nm (In case of glucose). This method tests for the presence of free carbonyl group (C=O), the so-called reducing sugars. This involves the oxidation of the aldehyde functional group present in, for example, glucose and the ketone functional group in fructose. Simultaneously, 3,5-dinitrosalicylic acid (DNS) is reduced to 3-amino,5-nitrosalicylic acid under alkaline conditions
Requirements:
DNSA
Sodium potassium tartarate
2 N sodium hydroxide (2N NaOH)
Dinitro salicylic acid (DNSA)
Distilled water
Sample
Procedure:
Prepare 20 mL of 2N NaOH.
Weigh 1 g DNSA and dissolve in 20 mL NaOH with the help of a magnetic stirrer
Weigh 30 g of sodium potassium tartarate and dissolve in 50 mL dH2O.
Slowly pour sodium potassium tartarate solution in the DNSA and NaOH solution and made the volume up to 100 mL (Note: Wait for the two to mix properly).
Decant the contents in a brown bottle. Filter if necessary.
Protocol:
Take eight tubes and label them as Blank and 1 to 7.
Make dilutions of glucose standards
Add 3 ml of DNSA reagent to all the eight test tubes. Mix well.
Keep in boiling water bath for 15 minutes.
After cooling to room temperature in a cold water bath, record the absorbance with a spectrophotometer at 540nm.
First, take the absorbance (OD) of Blank and make it zero.
Take the OD of all the tubes (No. 1-7). Wash the cuvettes each time after taking OD.
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