Food Analysis: Starch, Protein and Reducing Sugars

A Qualitative and Quantitative study of Food Analysis to test for the presence of starch, protein and for reducing sugars.

• Sorina Popa

Laboratory Partner: Chris Paterson

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Objectives:

The aims for this experiment are to carry out a number of qualitative procedures in order to identify different food traces such as starch, protein and glucose that are present or absent within the aqueous tests.

Introduction:

Food science is the application of biological, chemical and physical composition of food as well as the concepts that highlight food processing. The governance within the Food Science Industries are exceptionally strict when it comes to the quality and the safety of their manufactured products. The role of a Food Scientist is to examine the microbiological, biochemical and physical equities of food. The main three categories of food are proteins fats and carbohydrates.

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Benedict’s test was considered perfect for this experiment as this test is can detect a positive result for reducing monosaccharides or disaccharides sugars such as glucose and lactose. During the process of heating, the alkali in the Benedict’s reagent becomes highly reactive and it behaves as a strong reducing agent.The significant colour change that occurs from a clear blue colour to a brick red precipitate indicates a positive result for the presence of glucose within a food sample. The green/yellow colour change can indicate a vague presence of protein as well as the presence of glucose.

Starch is an example of a polysaccharide that is found mostly within plants. Plants use starch to store energy.The Iodine Test is extremely sensitive and can detect up to 0.00002M of a solution tested at a temperature of 20 °C. However, if the sample’s pH is low, the iodine solution’s reactions wouldn’t occur with the sample solution tested. Iodine solution determines the presence of starch most easily when the cell walls are damaged and broken down in order to chemically react with the starch grains. In the presence of starch there is a colour change from Brown to Blue/Black. It is expected for starch to be present within potatoes, flour, certain vegetables and cereals.

Proteina and amino acids are the building blocks of protein. The amino acids are linked by peptide bonds. Protein is highly found within meat, seeds and beans.The biuret test was considered ideal for this experiment as it can detect higher concentrations of protein.The reaction formed comes from an organic compound as its heated and a high temperature resulting to a positive test for protein. The biuret reagent is composed of diluted copper sulphate within a strong alkali.The colour change from blue to purple originates from the coordinate complex that is found between the cupric ions and the nitrogen atoms.The Bradford Test was also considered for this experiment as it its a rapid and highly sensitive method for testing for Protein. [1]

Materials: The materials were as in the ITT Biology1 Food Analysis Protocols Manual. [2]

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Methods: There were 4 different experiments carried out in order to test for different components withing different food samples tested. The Iodine Test, Benedict Test, Biuret Test and Bradford Test were carried out as per Itt Biology1 Food Analysis Protocols Manual. [2]

Results/Data:

Table1: Assay Results indicating the presence of reducing sugars applying Benedict solution on the different aqueous solutions tested in the laboratory: [6]

Table2: Assay Results indication the presence of Starch applying Iodine solution on the different aqueous solutions tested in the laboratory: [5]

Table 3: Assay Results indication the presence of Protein applying Biuret Reagent on the different aqueous solutions tested in the laboratory: [3]

Table 4: Assay Results indication the presence of Protein applying Bradford Reagent on the different aqueous solutions tested in the laboratory: [4]

Discussion:

The following table will indicate the expected results of the solutions tested in the laboratory: [7]

Solution A: From the data obtained there is a positive result for the presence of glucose as the colour obtained was Green. The colour Green shows that there was another trace element as well as the presence of Glucose. For the Iodine test the colour obtained was Yellow towards Brown which indicates there was a negative result for the presence of starch. There was a negative result for the presence of protein using the Biuret Reagent as the original colour Blue remained the same. However, when this solution was tested for the presence of protein using Bradford Reagent, there was a colour change from Brown to Light Blue indicating that there are small traces of protein present within this solution. This leads to a conclusion that solution A can be classified as being High Energy Glucose Drink diluted 1 in 20.

Solution B: From the data obtained it showed to have the presence of Glucose as the colour obtained was Green. The colour Green tells us that traces of protein has been present as well as Glucose. To sustain this statement, when solution B was tested using Bradford Reagent , it showed a positive result for the presence of protein due to the colour change from Brown to Blue. However there was no presence of Starch within this solution as the colour remained the iodine brown/yellow original colour. This leads to the conclusion that solution B might have been the Diet Carbonated Lemon& Lime Drink diluted 1 in 20.

Solution C: Looking at the data obtained, Reducing sugars are present within this solution as the colour changed from Blue to Green. The Iodine test showed a negative result for the presence of Starch as the colour remained Brown. However, traces of Protein was present when the Bradford Test was carried out. This signifies that the solution C can be the Carbonated Diet Lemon and Lime Drink diluted 1 in 1000.According to the expected results, the Carbonated Lemon and Lime Drink diluted 1 in 1000 showed to have a positive result for Reducing sugar, and Protein. However, since this solution was diluted 1 in 1000, it’s possible that the presence of protein didn’t show because of the insufficient amount of protein. The Bradford Test showed to have the ability to indicate small traces of protein.

Solution D: Analysing the data obtained the wasn’t any presence of Glucose in the Reducing Sugars Assay as the colour remained blue. There wasn’t any Starch present when Iodine solution was added in the Solution D due to no change in the colour i.e. Brown. However, the Biuret Test indicated a positive result for the presence of protein due to the colour change from Blue to Purple. As the Biuret test is known to detect large traces of protein, the presence of protein also came positive when the Bradford Reagent was used. Looking at the different solutions and their expected results, Solution D can be considered to be Sports Supplement diluted 1 in 10 since it is said it’s based on protein and not so much Carbohydrate based. This can be the reason why the Iodine and Benedict Test showed negative results.

Solution E– From the results obtained it indicated that there are traces of Glucose as the colour changed from Blue to Yellow/Brown. The colour brown isn’t the presence only for the presence of glucose which is orange. There are traces of a different component within the Solution E. There aren’t any traces of Starch when the Iodine Solution was added to a sample of Solution E. However, the extra trace element that appeared during the Bradford Test.The colour changed from Brown to dark Blue signifying traces of protein. When the solution was tested for protein using the Biuret Reagent, it showed a negative result as there was no colour change. As a conclusion, the Solution E appears to be Cow’s Milk diluted 1 in 20.

Solution F: Analysing the data obtained from carrying out different aqueous procedures, it showed that there is a negative result for the presence of Reducing Sugars as the colour remained Blue after boiling process. There was also a negative result for the presence of Starch when Iodine solution was added and the colour remained the colour of Iodine solution i.e. Brown/Yellow. However, there was a positive result using both Biuret and Bradford Reagents as the colour changes to Purple when Biuret Reagent was used and the colour changed to dark Blue when Bradford Reagent was used. Comparing the result from this solution to the other expected solutions, Solution F can be looked upon to be Liquidised Cauliflower Filtered and Diluted 1 in 5.

Solution G: From the results obtained it showed that there was a positive result for the presence of Glucose as there was a colour change from Blue to Brown. The colour brown also indicates there is another trace element present within this solution as well as Glucose. In the Iodine Test there was a positive result for the presence of starch as the colour change was Orange. This is an unusual colour as the actual positive colour indication for the presence of starch is Blue/Black. However, the colour orange can indicate there are more than one trace elements that are present within this solution. When the Bradford Test was carried out, a negative result was obtained as the colour did not change in Biuret and Bradford Test. From the data obtained, Solution G can be Diet Carbonated Lemon and Lime Drink diluted 1 in 10.

Solution H: From the results obtained it showed a negative result for reducing sugar as the colour remained Blue. However, there was a positive result for the presence of starch as the colour changed from Brown/yellow to Orange. There was also a positive result when the solution was tested for protein. When Biuret Reagent was used the colour didn’t change which leads to a negative result but when the Bradford Reagent was used there was a positive result as the colour changed into Light Blue. This can mean that the Solution H can be classified to be Wheat flour 0.5% w/v solution.

Conclusion:

The purpose of these Qualitative experiments was to analyse in depth the aqueous solutions given and tested for the presence of starch, traces of protein and for reducing sugars. The data collected from each solution was compared with the expected results from specific solutions from which some were diluted more than 5 times. The results obtained were remarkably close to the results expected. This concludes that the overall assays undertaken were a success due to the results obtained and discussions made.

References:

Books/Manuals:

[1] ITT Laboratory Skills Manual (2014-2015), Biology1, pg. 44-51

[2] ITT Biology Analysis Protocols (2014-2015)

[3] Malhotra VK (2003) 4^th Edition, Food Analysis, Practical Biochemistry for Students, Ch.48.

[4] Shanmugam S., Sathish Kumar T, Panneer Selvam K, (2010) Laboratory Handbook on Biochemistry, Eastern Economy Edition, pg:26-27

Online Links:

[5] British Nutrition Foundation (2004), Test for Starch, (Energy and Nutrients1995) (http://www.foodafactoflife.org.uk/attachments/92592385-dfb2-4ad6d61cf053.pdf) Accessed on 26^th October 2014 @10.00am.

[6] British Nutrition Foundation (2004), (Energy and Nutrients 1995) (http://www.foodafactoflife.org.uk/attachments/f4525d5b-0133-49b1e394c729.pdf) Accessed on 26^th October [email protected] 10.30am.

[7] Conde Nast (2014) Self Nutrition Data (http://nutritiondata.self.com/facts/beverages/7399/2) accessed on 26^th [email protected].