Food Testing Experiment - Science Lab 2 Courses - IPSE FPMIPA UPI Assignment

Science Laboratory 2

Biology: Food Testing

        I.            Experiment title: A Qualitative Test for Starch, Fat, Reducing Sugar, and Protein

      II.            Introduction:

Starch

Starch is a complex, sparingly soluble, polysaccharide of plants. It consist of two main components: amylose and amylopectin. The amylose stains blue-black with iodine solution. The solution of iodine used to test for starch contains potassium iodide and water in addition of iodine. The potassium iodide is necessary to dissolve iodine in water. This reagent changes from a brownish or yellowish color to blue-black when starch is present, but there is no color of monosaccharide or disaccharides. (Prima, Eka Cahya, 2017)

This is a simple test which shows whether food contains starch. When iodine solution is mixed with starch, it turns from brown to dark blue. As this happens with very small amounts of starch, iodine is a sensitive one. Starch forms as grains inside the living cells of plants. Iodine solution penetrates into the starch most easily when the cell walls have been destroyed and it reacts most readily when the starch grains are swollen. Both these things happen when plant foods are cooked. (British Nutrition Foundation, 2004)

Fat

Fats make up the largest category of lipids, and also go by the terms triacylglycerol, triglycerides, and glycerolipids. There are several types of fats which are saturated fat (Milk and cheese) and unsaturated fat (oils from plants). Fat does not evaporate from brown paper, but instead leaves a translucent spot.

If a drop of liquid (such as alcohol, water or oil) falls on paper, it makes a mark which is bright and translucent (lets light through) when the paper is held up to the light. With some liquids the mark disappears as soon as the liquid evaporates. Alcohol takes a few seconds to disappear, water takes about a minute, but oil remains, forming a permanent grease spot. In this way, paper provides a method of distinguishing between oil and other liquids. (British Nutrition Foundation, 2004)

Reducing Sugar

Carbohydrates with a free or potentially free aldehyde (RCHO) or ketone (RCOR’) group have reducing properties in alkaline solution. For monosaccharide, the aldose- and keto- groups carry out reducing sugar reactions. Common disaccharides such as lactose and maltose have at least one exposed aldose- or ketone- group and can give a positive reducing sugar reaction also. (Prima, Eka Cahya, 2017)

 

Some simple sugars, including glucose, can be made to reduce blue copper sulphate to red copper oxide. This reaction can be used as a test for some sugars. Copper suphate is mixed with other chemical to be used as Benedict’s solution which is used in the test. (British Nutrition Foundation, 2004)

Protein

            A nutrient found in food (as meat, milk, eggs, and beans) that is made up of many amino acids joined together, is a necessary part of the diet, and is essential for normal cell structure and function. (Merriam Webster, 2017)

In this test, the copper sulphate solution is used as an indicator. It will turn violet or purple if added to soluble protein. This is the Biuret Test which can be used for protein which dissolves in water, but not for insoluble material. (British Nutrition Foundation, 2004)

   III.            Method

·         Materials and Equipment

v  Materials

-          Starch solution 2 mL

-          Protein sample 2 mL

-          Vegetable oil 2 mL

-          Glucose solution 2 mL

-          Iodine solution

-          Benedict’s reagent

-          Biuret solution

-          Water

v  Equipment

-          Beaker 500 mL

-          Test tube (6)

-          Yellow paper (2)

-          Pipette (3)

-          Bunsen burner (1)

-          Test tube rack (1)

-          Tripod (1)

-          Wire gauze (1)

-          Matches (1)

·         Procedure

v  Food Testing: Starch

-         Two test tubes are prepared for this experiment

-     The first test tube is labelled as starch solution and the second test tube as water

-         2 mL (40 drops) of starch solution are added into the first test tube

-         2 mL (40 drops) of water are added into the second test tube as control

-         2-3 drops of iodine are added into each test tube

-         The test tubes are swirled to mix the solution

-         The changes are recorded

v  Food Testing: Fat

-        Two pieces of yellow paper are prepared for this experiment

-        2-3 drops of oil are added into the surface of first yellow paper, labelled as oil

-        2-3 drops of water are added into the surface of second yellow paper, labelled as water

-        Those two sheets of paper are let to dry

-        The differences are recorded 

v  Food Testing: Reducing sugar

-        Two test tubes are prepared

-      The first test tube is labelled as glucose solution and another one  is labelled as water

-        2 mL (40 drops) of glucose solution are added into the first test tube

-        2 mL (40 drops) of water are added into the second test tube as control

-        2-3 drops of benedict are added into each test tubes

-        Bunsen burner is set on under the tripod and wire gauze

-        Water is added into the beaker until half of the beaker

-        The beaker is put on the tripod by using wire gauze

-        Those two test tubes are placed inside the water

-        The water is boiled for about 5 minutes with the test tubes inside it

-        The changes are recorded

v  Food Testing: Protein

-        Two test tubes are prepared in this experiment

-        The first test tube is labelled as protein sample, and another test tube is labelled as water

-        2 mL (40 drops) of protein sample are added into the first test tube

-        2 mL (40 drops) of water are added into the second test tube as control

-        2-3 drops of biuret are added into each test tubes

-        The test tubes are swirled to mix the solution

-          The changes are recorded

   IV.            Result

Chemical Indicator	Samples	Changes
		Before	After
Iodine	Starch solution	White	Dark purple
	Water	Transparent	Transparent
Benedict’s reagent	Glucose solution	Transparent	Orange
	Water	Transparent	Transparent
Biuret solution	Protein solution	Transparent	Violet
	Water	Transparent	Transparent
Oil	First oiled paper	Transparent	Transparent part is left
	Second watered paper	Transparent	There is no transparent part left

     V.            

Discussion

·         Food Testing: Starch

Amylose in starch is responsible for the formation of a deep blue colour in the presence of iodine. The iodine molecule slips inside of the amylose coil. Iodine- KI reagent: Iodine is not very soluble in water, therefore the iodine reagent is made by dissolving iodine in water in the presence of potassium iodide. This makes a slips into the coil of the starch causing an intense blue-black colour. (O’Dette, 2016)

·         Food Testing: Fat

Fats and oils have higher boiling points, so at the room temperature, they cannot absorb enough heat to evaporate. When fat or oil is placed on a sheet of paper, it diffracts light. The diffracted light can pass from one side of paper to another side and produces a translucent spot. (A  mrita University, 2015)

·         Food Testing: Reducing sugar

Benedict’s test is used to test for simple carbohydrates. The Benedict’s test identifies reducing sugars (monosaccharide’s and some disaccharides), which have free ketone or aldehyde functional groups. Some sugars, such as glucose are called reducing sugars because they are capable of transferring hydrogen (electrons) to other compounds, a process called reduction. When reducing sugars are mixed with Benedict’s reagent and heated, a reduction reaction causes the Benedict reagent to change colour. The colour varies from green to dark red (brick) or rusty-brown, depending on the amount of and type of sugar. (Bera, 2016)

·         Food Testing: Protein

The reagent used in the Biuret Test is a solution of copper sulphate (CuSO₄) and potassium hydroxide (KOH). The KOH is there to raise the pH of the solution to alkaline levels; the crucial component is the copper (II) ion from the CuSO₄.

Copper Sulphate solution is a blue colour, but when the copper (II) ions are coordinated with the nitrogen atoms of these peptide bonds, the colour change is dependent on the number of peptide bonds in the solution, so the more protein, the more intense the change. When the peptides are very short, the solution turns a pink colour, rather than violet. (Mack, Steve, 2004)

   VI.            References:

Prima, Eka Cahya, et al. (2017). Science Laboratory Experiments II First Edition. Bandung: Universitas Pendidikan Indonesia.

amrita.olabs.edu.in. (2015). Qualitative Analysis of Oils and Fats. Retrieved 2 December 2017, from amrita.olabs.edu.in/?sub=73&brch=8&sim=210&cnt=1

Mack, Steve. (2004). How does biuret reagent cause a colour change with proteins?. Retrieved from www.madsci.org/posts/archives/2004-12/1102321490.Gb.r.html (accessed on Saturday, 02 December 2017 at 7:12 pm)

O’Dette, Philip. (2016). Why does the colour of iodine solution turn blue when starch is added to it?. Retrieved from https://www.quora.com/Why-does-the-color-of-iodine-solution-turn-blue-when-strach-is-added-to-it (accessed on Saturday, 2 December 2017 at 7:17 pm)

Bera, Sohini. (2016). Why is Benedict’s reagent used to test the presence of glucose in urine?. Retrieved from https://www.quora.com/Why-is-Benedicts-reagent-used-to-test-the-presence-of-glucose-in-urine (Accessed on Friday, 1 December 2017 at 7:22 pm)

British Nutrition Foundation. (2004). Testing Food for Starch. Retrieved from www.foodafactoflife.co.uk (accessed on Friday, 1 December 2017 at 3:22 pm)

British Nutrition Foundation. (2004). Testing Food for Protein. Retrieved from www.foodafactoflife.co.uk (accessed on Friday, 1 December 2017 at 3:40 pm)

British Nutrition Foundation. (2004). Testing Food for Fat. Retrieved from www.foodafactoflife.co.uk (accessed on Friday, 1 December 2017 at 3:55 pm)

British Nutrition Foundation. (2004). Testing Food for Sugar. Retrieved from www.foodafactoflife.co.uk (accessed on Friday, 1 December 2017 at 4:12 pm)

Merriam Webster. (2017). Definition of Protein for Students. Retrieved from https://www.merriam-webster.com/dictionary/protein (Accessed on Saturday, 2 December 2017 at 4:49 pm)

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