Reducing sugar by DNS method | 3, 5 Dinitrosalicylic acid (DNSA) method

Summary

This video explains the concept of reducing and non-reducing sugars, focusing on the chemistry behind them. It highlights that reducing sugars, like glucose and fructose, have free aldehyde or ketone groups, while sucrose, a disaccharide, is a non-reducing sugar due to the involvement of its functional groups in glycosidic bond formation. The video also details the DNS (3,5-dinitrosalicylic acid) method, which is used to estimate reducing sugar concentrations by measuring the color change in a reaction. The intensity of the color correlates with sugar concentration, allowing for accurate estimation using a standard curve.

Takeaways

• 😀 Reducing sugars have a free aldehyde or ketone group, which allows them to be oxidized.
• 😀 Glucose and fructose are examples of reducing sugars, with glucose containing a free aldehyde group and fructose containing a free keto group.
• 😀 Sucrose is a non-reducing sugar because both glucose and fructose in sucrose are involved in glycosidic bond formation, leaving no free aldehyde or ketone group.
• 😀 Reducing sugars are typically monosaccharides, while disaccharides like sucrose are not considered reducing sugars.
• 😀 The DNS method (Dinitrosalicylic Acid method) is used to estimate the concentration of reducing sugars.
• 😀 When reducing sugars are treated with DNS in a boiling water bath, DNS is reduced to 3-amino-5-nitrosalicylic acid, which forms an orange or brown color.
• 😀 The intensity of the orange color produced in the DNS reaction is directly proportional to the concentration of reducing sugars.
• 😀 The optical density (OD) of the orange color can be measured at 540 nm to estimate the reducing sugar concentration.
• 😀 A standard curve can be created by plotting the optical density against known concentrations of reducing sugars.
• 😀 The concentration of an unknown reducing sugar can be determined by comparing its optical density to the standard curve.

Q & A

What is the defining characteristic of a reducing sugar?

A reducing sugar contains a free aldehyde or ketone group that can participate in reactions, such as reducing other substances. Examples include glucose and fructose.

Why is sucrose not considered a reducing sugar?

Sucrose is not a reducing sugar because the aldehyde group of glucose and the keto group of fructose are involved in a glycosidic bond, leaving no free functional groups.

How do glucose and fructose differ in terms of their reducing properties?

Glucose has a free aldehyde group on its first carbon, making it a reducing sugar, while fructose has a free keto group on its second carbon, also making it a reducing sugar.

What happens when reducing sugars are treated with DNS in a boiling water bath?

When reducing sugars are treated with DNS (3,5-dinitrosalicylic acid) in a boiling water bath, the DNS is converted into 3-amino-5-nitrosalicylic acid, which exhibits an orange or brown color.

How does the concentration of reducing sugar affect the color intensity in the DNS method?

The intensity of the orange or brown color increases with the concentration of reducing sugar, providing a visual indicator of the sugar’s concentration.

What role does optical density play in estimating reducing sugar concentration?

The optical density (OD) of the color formed by the DNS reaction is measured at 540 nm. This OD is proportional to the concentration of reducing sugars in the sample.

How is a standard curve used in the DNS method?

A standard curve is created by plotting the optical density values of known concentrations of reducing sugars. This curve is then used to estimate the concentration of unknown samples based on their optical density.

What does the standard curve in the DNS method represent?

The standard curve represents the relationship between the optical density at 540 nm and the known concentrations of reducing sugars, allowing for the estimation of unknown sugar concentrations.

What is the importance of using DNS in the determination of reducing sugars?

DNS is important because it reacts with reducing sugars to produce a color change, which can be quantitatively measured to estimate the sugar concentration in a sample.

Why is the measurement taken at 540 nm in the DNS method?

The measurement is taken at 540 nm because this is the wavelength at which the orange or brown color formed during the DNS reaction absorbs light, allowing for accurate optical density readings.