TitleComparison of chemical composition of various food stuff

IntroductionMacromolecules are in all forms of life.  These organic compounds are carbohydrates, lipids and proteins. The presence of these macromolecules can be tested using different reagents.

Carbohydrates are made up carbon,oxygen and hydrogen.They can be categorized into two groups which are sugar and non-sugars.Sugar consist of monosaccharides and disaccharides while non-sugar consist of polysaccharides. Monosaccharides are the simplest form of sugar,disaccharides compose of two monosaccharides while polysaccharides are compose of long chains of monosaccharides unit that are bound together by glycosidic bonds.

Proteins are the building blocks of life. It is made up of long chains of amino acids linked together by peptide bonds. This composition is tested by using Biuret’s test.

Lipid are molecules that contain hydrocarbon and is the building block for structure of living things. It is a non-polar organic compound which is soluble in organic solvent such as alcohol. It consists of elements such as carbon, hydrogen and oxygen.

The carbohydrate,lipid and protein are tested using their specific reagent which results in specific colour changes.

MethodsIn the experiment for detection of carbohydrate,the materials and apparatus used are potato,iodine solution,microscope,glass slide,scalpel, measuring cylinder, sucker, Benedict’s solution,glucose solution,fruit juice,water bath,timer,dilute hydrochloric acid (HCl) , sodium bicarbonate (NaHCO3❑), fresh milk, sodium hydroxide (NaOH), copper sulphate (CuSO4❑), coconut oil, ethanol. The first experiment for starch, a potato was sliced thinly by using a scalpel.One drop of iodine solution was added to stain the potato.The stained potato was placed under the microscope and was observed using two different magnification which are x10 and x40.The stained cells of potato were observed and recorded in table 1.0

The second experiment of carbohydrate, which is reducing sugar, 1 cm3 of Benedict’s solution and 3cm3 of glucose solution was added into a test tube.The test tube was placed into the boiling water bath which is 90 degrees Celcius for 2 minutes.The test tube was removed from the water bath and the changes in colour of the solution were recorded in table 1.1

For the third experiment for carbohydrates, which is non-reducing sugar, 1 cm3 of Benedict’s solution and 3cm3 of fruit juice was added into a test tube. The solution was observed and the colour changes were recorded in Table 1.2. Then, 3 cm3 of fruit juice and 1cm3 of dilute hydrochloric acid (HCl) was added into a

another clean test tube. The solution was boiled in a water bath at 90 degrees Celcius for 3 minutes. The test tube was removed from the water bath and left to cool at room temperature for 5 minutes. After cooling, sodium bicarbonate was added into the solution to neutralize the mixture until the foaming stops. Then, the Benedict’s test was repeated on the mixture. The colour changes were observed and recorded in Table 1.2.

The next group of test was protein. 2cm3 of sodium hydroxide (NaOH) was added into 2cm3 of fresh milk in a test tube followed by four drops of copper(II) sulfate (CuSO4 ¿. The mixture was shaken gently. The colour changes were observed and recorded in table 1.3.

For the next experiment which is detection of lipid, a measuring cylinder is used to measure 2cm3 of ethanol. The ethanol is then poured into a test tube. A few drops of coconut oil is then added to the test tube using a sucker. The test tube is shaken gently and the changes is observed. A few drops of sodium hydroxide (NaOH) is added into the solution. Then the changes is observed again.

Results

Table 1.0 Iodine test for the presence of starch

Magnification of potato cells image observed under microscope

Obeservation

X4 Starch granules are stained blue black by iodine solution.

X10 Starch granules are stained blue black by iodine solution.

Table 1.1 Reducing sugarSolution Observation1cm3 of Benedict’s solution + 3cm3 of glucose solution

Solution changes in colour from blue to brick red precipitate

Table 1.2 Non-reducing SugarSolution Observation1cm3 of Benedict’s solution + 3cm3 fruit juice

Solution changes in colour from orange to green

1cm3 of dilute hydrochloric acid (HCl) +3cm3 of fruit juice + sodium bicarbonate (NaHCO3)

Solution changes in colour from orange to green, then to orange - yellow

Table1.3 Biuret test for the presence of proteinSolution Observation

2cm3of fresh milk+2cm3of NaOH No changes

2cm3of fresh milk+2cm3of NaOH+CuSo4 Solution changes in colour to violet.

Table1.4 Emulsion test for the presence of lipidSolution Observation

Coconut Oil + 3cm3 Ethanol Cloudy with emulsion

Coconut Oil + 3cm3 Ethanol + NaOH Cloudy

DiscussionIn the carbohydrate experiment for the starch,the colour of iodine changes from brown to blue black when in contact with the potato’s cells.Starch has 2 components which are amylose and amylopectin.The amylose component of starch has helical structure.The iodine is trap inside the helix and this complex gives intense blue colour.

Reducing sugars carry out a type of chemical reaction called as reduction.The Benedict’s test is used to test the reducing sugars and in the process the reducing sugars are oxidized.When the glucose is heated with Benedict’s solution the glucose decomposes to form products that reduce Cupric (Cu2+¿ ¿) ions to Cuprous (Cu+¿¿)ions. The solution changed to brick red precipitate upon heating in the water bath with the temperature of 90 degrees Celcius for 2 minutes.

In the experiment to determine the presence of non-reducing sugar, Fehling’s test was carried out. 1cm3Benedict’s solution was added into the 1cm3 of fruit juice to test the presence of non-reducing sugars. When the solution turned from orange to green, the negative result shows that a trace of non-reducing sugars is present. In a separate test tube, 1cm3 of dilute hydrochloric acid and 3cm3of fruit juice were added together and placed in a water bath of 90 degrees Celcius to hydrolyse the glycosidic bond. Sodium bicarbonate was added into the mixture until it stops fizzing, as to neutralize the solution. The solution turned from orange to yellow and it proved that sucrose is present in the solution.

The presence of protein is detected by using Biuret’s test. When 2cm3 of sodium hydroxide (NaOH) was added to 2cm3 of fresh milk, there is no change in colour. The mixture started to change to violet colour when four drops of copper(II)sulphate solution were added.This is explained when cupric ion in alkaline medium forms a violet coloured complex with peptide bond of protein.The test is answered by compound having two or more peptide bonds.

Emulsion test is to determine the presence of lipid. Lipids do not dissolve in water but it dissolves in ethanol. This characteristic is used in Emulsion test. A few drops of coconut oil is added into a test tube containing 2cm3 of ethanol and is gently shaken. The reaction between lipid and ethanol causes the solution to turn cloudy. When a few drops of sodium hydroxide is added into the mixture, the solution forms an emulsion. This is known as emulsification. A small globule is formed in the solution which makes it appear cloudy.

Conclusion

The experiment showed the presence of specific chemical composition in food when tested with the specific reagent. Starch in the potato reacted to iodine which proved the presence of starch. The glucose solution showed colour changes to brick red precipitate when added with Benedict’s solution. In the third experiment, the neutralize fruit juice changed to tangy orange colour when reacted with Benedict’s solution which showed the presence of non-reducing sugar. Biuret’s test proved the presence of protein in the fresh milk. The Suldan’s test showed emulsion in coconut oil.