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Lab Report 1...

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BIO121 Experiment 1-Detecting Compounds Made by Living Things Part (A)-Test for Carbohydrate i)

Test for starch

Objective: To test the presence of starch using Iodine test. Methods: 1) Six test tubes were prepared and labelled as #1 to #6. 2) At test tube #1 to #6, extract of soya bean, peanut, milk, extract of onion, extract of potato and starch solution (act as the positive control) were added into the test tube respectively. 3) In each test tube, 3 drops of iodine solution were added and was mixed well. 4) The colour changes of each test tube were observed and recorded.The presence of starch in each test tube was determined based on the results observed. Results: Test tube

#2

Substance Extract of Soya Bean Peanut

#3 #4 #5

Milk Extract of Onion Extract of Potato

#6

Starch Solution (+ve control)

#1

Colour change No colour change From yellow to blue-black No colour change No colour change From yellow to blue-black From yellow to blue-black

Presence of starch No Yes No No Yes Yes

Discussion: Starch is a polysaccharide made up of glucose units joined by glycosidic bonds which act as the main energy reserved in plants. In the presence of starch ,iodine solution as the indicator changes colour from yellow to blue-black. This is due to the action of a formation of an intermolecular charge-transfer complex upon the addition of an aqueous solution of a triiodide anion which is produced through the process of dissolving iodine in aqueous potassium iodide solution. Based on the results ,the positive control, starch solution in test tube #6 has shown the expected results by changing the colour of iodine solution from yellow to blue-black. Among the food samples, peanut and the extract of potato from test tube #2 and#5 respectively have shown colour changes from yellow to blue-black after iodine solution is added, indicating that starch is present whereas the extract of soya bean ,milk and the extract of onion from test tube #1,#3 and #4 respectively does not show any colour changes and remains yellow after iodine solution is added, indicating that starch is not present. However, the results are not as expected, as it has been known that soya bean should contain starch, this discrepancy is probably caused 1

by the amount of starch found in soya bean is very less. This explains why the presence of starch in soya bean is unable to be tested. Conclusion: Iodine test can be used to detect the presence of starch. Peanut and the extract of potato contain starch.

ii)

Test for glucose

Objective: To test the presence of a reducing sugar using Fehling test. Methods: 1. Six test tubes were prepared and labelled as #1 to #6. 2. At test tube #1 to #6, extract of soya bean ,peanut ,milk ,extract of onion ,extract of potato and glucose solution (act as the positive control) were added respectively into the test tube. 3. In each test tube, 10 drops of Fehling I solution and 10 drops of Fehling II solution were added and was mixed well. 4. The test tubes were placed in a hot water bath for 5 minutes. 5. The colour changes of each test tube were observed and recorded .The presence of the reducing sugar in each test tube was determined based on the results observed. Results: Test Substance tub e #1 Extract of Soya Bean #2 Peanut #3 Milk #4 Extract of Onion #5

Extract of Potato

#6

Glucose Solution (+ve control)

Colour change

No colour change No colour change From blue to yellow From blue to yellowish brown From blue to yellowish orange From blue to reddish orange

Presence of reducing sugar

No No Yes Yes Yes Yes

Discussion: Glucose is a monosaccharide which is one of the important component of many carbohydrates such as maltose, lactose etc, and is also an important source of energy in all living organisms. In the presence of a reducing sugar ,Fehling solution changes colour from blue to reddish orange. This is due to the oxidizable open chain aldehyde and ketone found in alkaline solution which reacts with Fehling solution by reducing copper(II) ions to copper(I) oxide. Fehling solution is made into 2 different solutions where Fehling I solution is blue in colour whereas Fehling II solution is a clear solution. Based on the 2

results ,the positive control, glucose solution in test tube #6 has shown the expected results by changing the colour of Fehling solution from blue to reddish orange. Among the food samples, milk, extract of onion and the extract of potato in test tubes #3, #4 and #5 respectively have shown colour changes after Fehling solution is added, indicating that a reducing sugar is present whereas the extract of soya bean peanut does not show any colour changes and remains blue after Fehling solution is added, indicating that a reducing sugar is not present. However, the results are not as expected, as it has been known that soya bean should contain a reducing sugar, this discrepancy is probably caused by the amount of reducing sugar found in soya bean is very less. This explains why the presence of a reducing sugar in soya bean is unable to be tested.

Conclusion: Fehling test can be used to detect the presence of reducing sugar. Milk, extract of onion and extract of potato contains a reducing sugar.

iii)

Test for sucrose

Objective: To test the presence of reducing sugar using Fehling test. Methods: 1. Two test tubes were prepared and labelled as #1 and #2. 2. At test tube #1 and #2, a sugar solution of a mixture of glucose and fructose solutions were added to both test tubes. 3. In test tube #1, 4 drops of hydrochloric acid solution (HCL) were added and was mixed well . 4. Both test tubes were placed in a hot water bath for 5 minutes. 5. After 5 minutes, both test tubes were taken out to be cooled down . 6. After both test tubes were cooled, 10 drops each of Fehling I solution and Fehling II solution were added to both test tubes and was mixed well. 7. Both test tubes were placed in a hot water bath once again for 5 minutes. 8. The colour changes of both test tubes were observed and recorded .The presence of reducing sugar in each test tube was determined based on the results observed.

Results: Test Substance tub e #1 Sugar solution with HCL #2 Sugar solution only

Colour change

Presence of reducing sugar

From blue to reddish brown

Yes

No colour change

No

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Discussion: Sucrose is a disaccharide which is composed of glucose and fructose. In the presence of a reducing sugar ,Fehling solution changes colour from blue to reddish brown. This is due to the oxidizable open chain aldehyde and ketone found in alkaline solution which reacts with Fehling solution by reducing copper(II) ions to copper(I) oxide. Fehling solution is made into 2 different solutions where Fehling I solution is blue in colour whereas Fehling II solution is a clear solution. Based on the results, the sugar solution with HCL added in test tube #1 has shown the expected results by changing the colour of Fehling solution from blue to reddish brown, indicating that a reducing sugar is present whereas in test tube #2, the colour of pure sugar solution remains unchanged, indicating that the sugar solution which is pure sucrose solution does not have the presence of reducing sugar. This is because sucrose do not have an aldehyde functional group and cannot reduce cooper (I) solution to copper (II) solution. Therefore, an aqueous solution of hydrochloric acid is added to hydrolyse its constituent monosaccharides in order to proceed with the Fehling test to show the presence of reducing sugar. This explains why the sugar solution with HCL added shows the presence of a reducing sugar. In conclusion, the outcome has reached my expectations. Conclusion: Fehling test can be used to detect the presence of reducing sugar. Sucrose solution is not a reducing sugar.

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Part (B)-Test for Protein Objective: To test the presence of protein using Millon’s test. Methods: 1. Seven test tubes were prepared and labelled as #1 to #7. 2. At test tube #1 to #7, extract of soya bean ,peanut ,milk ,extract of onion ,extract of potato ,albumin solution (act as the positive control) and water (act as negative solution) were added into the test tube respectively. 3. In each test tube, 5 drops of millon’s solution were added and was mixed well. 4. The test tubes were placed in a hot water bath for 5 mins. 5. The colour changes of each test tube were observed and recorded .The presence of protein in each test tube was determined based on the results observed. Results: Test tube #1 #2

Substance Extract of Soya Bean Peanut

#3

Milk

#4

Extract of Onion

#5

Extract of Potato

#6

Albumin Solution (+ve control) Water (-ve control)

#7

Colour change From colourless to Brick-red From colourless to Brick-red From colourless to Brick-red From colourless to Brick-red From colourless to Brick-red From colourless to Brick-red No colour change

Presence of protein Yes Yes Yes Yes Yes Yes No

Discussion: Albumin also known as egg white is a protein that is most commonly found in the blood to provide the needs of maintaining growth and repair tissues. In the presence of protein, millon’s solution changes colour from colourless to brick-red. This is due to the action of detecting the presence of soluble proteins mainly phenolic compounds in the solution. Based on the results, the positive control, albumin solution in test tube #6 has shown the expected results by changing the colour of millon’s solution from colourless to brick-red. All of the food samples from test tube #1 to #5 have shown colour changes after adding millon’s reagent, indicating that protein is present. However, the negative control, water in test tube #7 has shown no colour change despite the addition of millon’s reagent because water does not contain any phenolic compounds. In conclusion, the outcome of this experiment have reached my expectations. 5

Conclusion: Millon’s test can be used to detect the presence of protein. All of the food samples tested which are extract of soya bean, peanut ,milk ,extract of onion ,extract of potato contains protein.

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Part (C)-Test for Fat Objective: To test the presence of fat using Sudan III test. Methods: 1. Six test tubes were prepared and labelled as #1 to #6. 2. At test tube #1 to #6, extract of soya bean, peanut ,milk ,extract of onion ,extract of potato and vegetable oil (act as the positive control) were added into the test tube respectively. 3. To test tube #2, deionised water was added to dilute the solid peanut. 4. In each test tube, 10 drops of sudan III solution were added and was mixed well. 5. The mixtures in each test tube were shaken for 3 mins. 6. The test tubes were placed vertically and rested for 30mins without any external interference. 7. The colour changes of each test tube were observed and recorded. The presence of fat in each test tube was determined based on the results observed. Results: Test tube #1 #2 #3 #4 #5 #6

Substance Extract of Soya Bean Peanut Milk Extract of Onion Extract of Potato Vegetable oil (+ve control)

Observations Two layers formed Two layers formed Two layers formed Two layers formed Two layers formed Colour changes from red to Reddish-orange

Presence of fat Yes Yes Yes Yes Yes Yes

Discussion: Vegetable oil are unsaturated fats extracted from plants which is normally used for cooking, baking and etc. In the presence of fat, a red-stained oil layer will be separated out creating a double layer after sudan III solution is added. This is because sudan III solution is a lipid-soluble dye therefore it only dissolves in non-polar compounds. As water is a polar compound, it will not dissolve in water and the solution therefore separates, creating a double layer. Based on the results, the positive control, vegetable oil in test tube #6 has shown the expected results by changing the colour from red to reddishorange. It does not show the double layer effect as water is not present in vegetable oil. The food samples in test tube #1 to #5 have all shown the double layer effect by dying the solution into milky pink and separates the fat layer, indicating that fat is present. However, the double layer in test tube #1 and #3 is not as visible as the others due to the fat content in both substance is not as abundant as the others but instead a pink precipitate can be seen clearly which indicates that fat is present in both substance. In conclusion, the 7

outcome of the experiment has reached my expectations in spite of having some difficulties in spotting the double layer formed. Conclusion: Sudan III test can be used to detect the presence of fat. All of the food samples tested which are the extract of soya bean, peanut, milk, extract of onion, extract of potato contain fat.

QUESTIONS 1. Explain why all sugar-containing materials do not show a positive test for sugar when tested with Fehling’s solution. ANS: This is because some of the sugar such as sucrose is a non-reducing sugar. Therefore, a negative result of no colour changes is obtained when a fehling test is conducted. 2. Do any of the foods tested have more than one compound present? ANS: Yes, all of the food tested have more than one compound present. The extract of soya bean have the presence of starch, reducing sugar, protein and fat; Peanuts have the presence of starch, protein and fat; Milk have the presence of a reducing sugar, protein and fat; The extract of onion have the presence of a reducing sugar, protein and fat; The extract of potato have the presence of starch, a reducing sugar, protein and fat. 3. What is the practical value of food testing? ANS: This is to enable us to understand more about the nutritional value of a certain food we are consuming in a daily basis. Besides that, a balanced diet can be planned through food testing in analysing and measuring the nutritional values of each meal.

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