Question

Identify the disaccharide that fits each of the following descriptions: a. not a reducing sugar b. composed of two glucose units c. also called milk sugar d. hydrolysis gives glucose and fructose

Short answer

a. Sucrose, b. Maltose, c. Lactose, d. Sucrose

Step-by-step solution

Identify the disaccharide that is not a reducing sugar

Sucrose is not a reducing sugar. This is because it does not have a free anomeric carbon atom in its structure, which is required to be a reducing sugar.

Determine the disaccharide composed of two glucose units

The disaccharide that is composed of two glucose units is maltose. Maltose is formed from the condensation of two glucose molecules.

Identify the disaccharide also called milk sugar

Lactose is also called milk sugar. It is found in milk and is composed of glucose and galactose.

Determine the disaccharide that hydrolysis gives glucose and fructose

Sucrose, upon hydrolysis, gives one molecule of glucose and one molecule of fructose. It is commonly known as table sugar.

Key concepts

Not A Reducing Sugar

A sugar is classified as a reducing sugar if it has a free anomeric carbon atom that can act as a reducing agent. In simpler terms, if this atom can donate electrons to another compound, the sugar is termed reducing. An example of a disaccharide that is not a reducing sugar is sucrose. In sucrose, the anomeric carbons of both glucose and fructose are involved in the formation of the glycosidic bond, leaving no free anomeric carbon. This bond arrangement prevents sucrose from participating in redox reactions, making it a non-reducing sugar.
Understanding this concept is crucial in biochemistry and food science, as it affects the behavior of sugars in various reactions.

Two Glucose Units

Disaccharides are sugars formed by the combination of two monosaccharides. Maltose is an example of a disaccharide composed of two glucose units. It is formed through a condensation reaction, where a molecule of water is removed as a glycosidic bond is created between the two glucose molecules.
Maltose can undergo hydrolysis in the presence of enzymes like maltase or acids to re-form the two glucose molecules. This process is important because it helps in digesting starchy foods, breaking them down into simpler sugars that the body can use for energy.
Maltose is less sweet than sucrose, which is why it’s commonly used in brewing and fermentation rather than as a sweetener in foods.

Milk Sugar

Lactose is often referred to as milk sugar because it is the primary carbohydrate found in milk and dairy products. It consists of one unit of glucose and one unit of galactose. In the body, the enzyme lactase is responsible for breaking down lactose into these two simpler sugars for absorption.
Many people, especially adults, are lactose intolerant, meaning they lack sufficient lactase to digest lactose properly. This can lead to gastrointestinal discomfort after consuming dairy. Understanding lactose and its properties is crucial for those dealing with dietary restrictions and for the dairy industry to create lactose-free products.
Despite its less sweetness, lactose plays a vital role in the nutrition derived from milk, particularly in infancy.

Hydrolysis of Disaccharides

Hydrolysis is a chemical process where water breaks down compounds. When disaccharides undergo hydrolysis, they break down into their monosaccharide components. Sucrose hydrolysis, specifically, results in the formation of one molecule of glucose and one molecule of fructose. This process can occur under acidic conditions or with the help of specific enzymes like sucrase.
This reaction is significant in digestion and in the food industry. In digestion, it allows the body to utilize the energy stored in complex sugars. In food industries, it’s used to invert sugar syrup, which is sweeter and often used in confectioneries and beverages for enhanced sweetness and texture.
Sucrose is commonly known as table sugar and is derived mainly from sugarcane or sugar beets.