Estimation of Reducing Sugars by DNS Method

This flashcard set covers the biochemical principles of the DNS method for estimating reducing sugars, including the chemical structures of sugars, the reaction process, and measurement parameters.

Carbohydrates

Molecules consisting of carbon, hydrogen, and oxygen ($C + H + O$) that serve as fuel for storage and energy release, composed of polyhydroxy-aldehydes or ketones.

Glucose

A reducing sugar with the formula $C_6H_{12}O_6$ that contains an aldehyde group ($H-C=O$) and hydroxy or alcohol groups.

Fructose

A reducing sugar with the formula $C_6H_{12}O_6$ that contains a ketose group ($R-C-R$).

Reducing Sugars

Sugars that harbor a free carbonyl ($C=O$) in the form of aldehyde or ketone groups, such as glucose and fructose.

Non-reducing Sugar

A sugar that lacks a free carbonyl ($C=O$) group; for example, sucrose.

DNS Method

A technique for the estimation of reducing sugars where 3,5-dinitro-salicylic acid is reduced to 3-amino-5-nitrosalicylic acid under alkaline conditions.

3,5-dinitro-salicylic acid (DNS)

The reagent used in the DNS method that changes from yellow to orange/red upon reduction by a sugar's free carbonyl group.

3-amino-5-nitrosalicylic acid

The reduced form of DNS produced during the reaction with reducing sugars.

Gluconic Acid

The carboxylic acid produced when glucose is oxidized during the DNS reaction.

540 nm

The specific wavelength (within the range of $510-550\,nm$) used to measure the absorbance of the resulting mixture in the DNS method using a spectrophotometer.

Cysteine

An example of a reducing substance that can cause interference and lead to the overestimation of results in the DNS method.

Specificity of DNS Method

The method detects all reducing sugars, though different sugars produce different color intensities.