What is benedict's test for monosaccharides

Benedict's test for monosaccharides is an analytical chemistry test used to identify monosaccharides, which is produced by a mixture of hydrochloric acid and sulfuric acid. Hydrochloric acid reacts with the monosaccharide to form hydrogen chloride and the corresponding alcohol; for example, glucose forms gluconaldehyde. The concentration of hydrogen ion in the solution is measured with a pH meter or colorimeter. At acidic pH values above 2, molecules containing an aldehyde group are deprotonated to their corresponding acids that can react with sulfuric acid to produce sulfonic acids; for example, gluconaldehyde reacts with sulfuric acid to form glucono-1,5-lactone.

Uses of monosaccharides 

1. Vitamins

Carbohydrate is a substance compound of carbon, hydrogen, and oxygen. Two important carbohydrate are monosaccharides and disaccharides. Monosaccharides are the smallest units of carbohydrates. Monosaccharides contains an aldehyde or ketone group. Yeast extract contains monosaccharide yet with other elements like protein, minerals and vitamins. Monosaccharide is part of glycolysis which is involved in production of energy in living organisms from glucose . Caramel and corn syrup also contain monosaccharide as sweetening agent for food recipes.

2.Sweeteners

Monosaccharides are widely used in the food industry in gourmet food, bakery and pastry products, canned fruit and jelly. Some of these products are: jams, jellies and fruit spreads, canned fruits and tomatoes, cereal products, milk drinks and yogurt. It also acts as a sweetener of drinks like beer. Monosaccharide is also added to infant formula to support growth of infants.

3.Preservatives

Monosaccharides are used as preservatives in breads or other baked product to prevent mold growth on the product; for example fructose can be used for preservation of bread.

4.Pharmaceuticals

Monosaccharide is used as a sweetening agent of medicinal tablets. It can be traced in cough drops, throat lozenges and cough syrup.

5.Cleaning agent and disinfectants

Diluted monosaccharides are popular cleaning agents to clean stains in clothes and kitchen utensils; however it is not effective to remove tough stains like cream or butter. Monosaccharide is an element of some disinfectants as well; for example quassin is a monosaccharide that can be used in hair tonic, shampoo or lotion to prevent dandruff and strengthen hair follicles.

6.Sparkling wines

Monosaccharides like saccaromyces cerevisiae is a yeast used to produce sparkling wines. It is responsible for carbon dioxide production in the wine. Saccharomyces cerevisiae is also used to produce beer and cider. Beer contains some saccharomyces cerevisiae strains that are a source of monosaccharide as well.

7.Bread and baked items

Monosaccharides is used as a yeast in baking, in order to produce carbon dioxide to leaven the product. Monosaccharide is also used in supplement to make bread more nutritious; it can be added to bread dough or added into sugar syrup while baked.

8.Fruit juices and beverages

Monosaccharide is added to fruit juices and various sodas to make them more sweet; for example, aspartame is a monosaccharide used as a synthetic sweetener in many diet drinks. It has lower calories compared to sucralose or sugar which makes it ideal for diet food.

Preparation of monosaccharide solution

The first step in preparing the Benedict's test is to dissolve the monosaccharides that you have into a solution. A strong alkali or strong acid is added into a solution with a monosaccharide until no solid remains. Strong alkali is added if the monosaccharide has an aldehyde group while strong acid is used on ketone group containing monosaccharides. In this experiment, Benedict's test for monosaccharides. will be prepared using glucose and hydrochloric acid.

Preparation of solution

Glucose is dissolved in water to make a 100 ml Benedict's test. Add hydrochloric acid into 50 ml to dissolve the glucose.

Procedure of the Benedicts' test

Locate the colorimeter's pH range on the container. Check whether or not it is in the correct range before starting the test. Remove both drops of Benedict's solution and sample monosaccharides into each of them. Record the results on graph paper for later understanding. Record readings to show any change in pH value over time (usually after half an hour). Repeat step 3 and 4 with another drop from each container until all samples have been taken from both containers.

Observation of results

Both forms of Benedicts' test will produce different results. In this experiment, the sample monosaccharide solution that was produced by hydrochloric acid and glucose will produce a pH change within the range of 1-2. The result is acidic and the Benedict's test is meant to identify an aldehyde group as it produces a reaction that gives off hydrogen chloride and water. The result of glucose, which is a monosaccharide containing an aldehyde group is acidic. Whereas, the monosaccharide solution that was produced by sulfuric acid and glucose has a pH near 14 which is alkali and will be neutral in nature. This explains Benedict's test for monosaccharides.