Biological tests and PAGs

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Food tests

Test for sugar: Benedict's solution

Benedict's solution is used to detect the presence of a reducing sugar. The copper ion (Cu+2) contained within the Benedict's reagent is reduced to Cu+ if it reacts with the free aldehyde or ketone group present in all monosaccharides and some disaccharides. In order for the reactions to take place, the reagents must be heated (roughly 5 minutes at 85°C).

A positive test is noted by a color change to green, orange, brick red or brown. Green indicates a small amount of reducing sugar present, orange and brick red indicate increasingly larger amounts of the reducing sugar is present, and dark brown indicates the most reducing sugar present. A negative result is seen as blue (no color change). Sucrose is the most common non-reducing sugar.

Test for protein: Biuret reagent

The Biuret Test is used to determine the presence of peptide bonds in protein. The Biuret test for proteins may also be extended to quantitatively measure the concentration of total protein using spectrometric methods.

Test for lipids: Emulsion test

The Ethanol Emulsion Test determines the presence of a broad group of naturally occurring compounds known as lipids. Lipids consist of fats and oils. Other lipid tests include the Grease Spot Test and the Sudan Stain Test which will stain lipid cells red. The Grease spot test is performed on fats - lipids which are solid at room temperature. Sudan stain colours lipids red, but is a less common bench reagent than ethanol. The Ethanol Emulsion Test is the most common test amongst the three.

Test for carbohydrates: iodine solution

There are many tests for carbohydrates including Molisch’s Test and reduction tests. but the most commonly used of these is iodine solution. In this, iodine solution is used to detect the presence of starch by turning a blue-black colour. Iodine intercalates into the helical structure of starch polymers resulting in a colour change from yellow to bluish-black. It can also be used to detect the presence of carbohydrates.

key words:

Reducing sugar: 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

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Chromatography

Chromatography is used to separate compounds in a mixture. there are at least three different types of chromatography, simple paper, e one in a tube and thin layer chromatography.

Separating amino acids using thin layer chromatography

Thin layer chromatography (TLC) is a technique used to separate the individual components of a mixture. The technique can be used to separate and identify a mixture of amino acids in solution. There are two phases, the stationary phase and the mobile phase which involves an organic solvent. The mobile phase picks up the amino acids and moves through the stationary phase and the amino acids are separated.

In the stationary phase a thin layer of silica gel (or another adhesive substance) is applied to a rigid surface, for example a sheet of glass or metal. Amino acids are then added to one end of the gel. This end is then submerged in organic solvent. The organic solvent then moves through the silica gel, this is known as the mobile phase.

The rate at which the different amino acids in the organic solvent move through the silica gel depends on the interactions (hydrogen bonds) they have with the silica in the stationary phase, and their solubility in the mobile phase. This results in different amino acids moving different distances in the same time period resulting in them separating out from each other.