Determine the presence of reducing sugar, protein and starch in the food products by using Benedict test, Biuret test and Iodine test,

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Chapter 1 – Chemistry of Life

Determining the Presence of Certain Nutrients

Kieun Bae, DP2 - Biology HL


 The idea of this experiment was to plan the diet for a day and determine if the diet plan contains the necessary nutrients, by testing the food products with chemicals. In this way, we would have better idea about what kind of food product should be included in the daily diet. The meal-plan of the day we have made was following:

  • Breakfast
  • milk
  • cereal
  • Lunch
  • bread
  • juice
  • cheese
  • apple
  • Dinner
  • pasta
  • lattice
  • meat
  • tomato
  • yogurt
  • red wine
  • onion

This was planned by discussing the actual food products we commonly take in a day. There are few diary products that are commonly known to contain a lot of protein, necessary carbohydrates for each meal (bread, pasta and cereal) as well as the vegetables that contain many various healthy nutrients including glucose (simple sugar), vitamins, minerals etc. Also, there is meat that is supposed to contain some fatty substances and protein.

 The essential nutrients that we need daily for our body to function properly are mainly six. They are water, carbohydrates (glucose, starch, sucrose etc.), proteins, fats, vitamins and minerals.[1] In the lab, we are going to find out the presence of different nutrients and decide whether the planned list of daily diet food products is good enough to provide the necessary nutrients.

 The chemical tests that are used for the experiments are: Benedict test, Biuret test and Iodine test, which test for glucose, protein and starch. All the tests indicate if the product contains the certain type of nutrients by the change of colors. One more testing would be HCl/Benedict test, and the purpose of this test will be explained further. Let me explain them, one by one, into details.

  1. Benedict test[2]

 Benedict test is used to determine the presence of reducing sugar which is monosaccharide and some disaccharides.  However, non-reducing sugars such as sucrose won’t have Benedict reaction. In order to have the result with Benedict test, the non-reducing sugars first would have to be transformed into reducing sugars. This can be done by adding hydrochloric acid (HCl) and hydrolyzing them. Here is the purpose of HCl/Benedict test.[3] So basically, Hcl/Benedict test is used for determination of sucrose.

The Benedict reagent has to be added to the substance and has to be heated in order to make the reaction occur and observe the color.  

The color change depends on the amount of reducing sugar in the substance. It differs like this:

Green   Yellow   Orange   Red   Brown

 More and more the sugar there is, it will be closer to red & brown. Commonly, though, it is known to show the orange color.

  1. Biuret test[4]

Biuret reagent detects the presence of peptide bonds, which hold the amino acid molecules together and build up proteins. This basically means that Biuret test is used to determine the presence of protein in the substance.

The reagent has a color of light-blue, and it includes sodium hydroxide (10% NaOH) and copper (II) sulphate (1% solution of CuSO4). The indicator-color is purple.

  1. Iodine test[5]

  This test indicates the presence of starch in the substance. The starch is the stored form of glucose (monosaccharide’s that form carbohydrates) in plants. We can easily find rich amount of starch in potatoes, rice, cereal etc).[6] Iodine, itself has a brownish yellow color but when it comes in contact with the substance that contains starch, it turns blue black.

 In order to make sure the test works for the food products, we pre-tested with pure protein, starch and glucose substances and collected data. Of course, we needed a control and therefore we tested distilled water as well. The data of this pre-test as well as the actually experiment data will be presented later in Data Collection and Data Process section.

 It is a shame that the tests are only for determining the presence of protein, non-reducing & reducing sugars such as starch, sucrose, etc. It basically means that we can get a conclusion only for carbohydrates and proteins that are only two out of six of the essential nutrients. More detailed evaluation will be included in Evaluation part.

 Research Question

 Determine the presence of reducing sugar, protein and starch in the food products by using Benedict test, Biuret test and Iodine test, in order to decide whether the diet planning was successful enough to allow a person to take in the necessary nutrients (carbohydrates and proteins).

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 Using the common background knowledge I have read or seen in various diet-related TV programs as well as my biological knowledge, my hypothesis is following: The meal-plan for a day that we have made does contain all the nutrients that could have been tested for, therefore it is possible to say that the meal-plan was pretty successful; however due to the limitation of testing methods, some of the nutrients that are needed for proper body functioning such as vitamins, minerals, fatty acids could not be determined to be present.


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