Chemical Tests for Nutrients

The Test for STARCH

The Test for STARCH Reminder: Starch is a complex carbohydrate, which is our major source of food energy.

The Test for STARCH Place a few drops of the unknown in a well on a spot plate

The Test for STARCH Place a few drops of the unknown in a well on a spot plate Add about 2 drops of Iodine Solution

The Test for STARCH Place a few drops of the unknown in a well on a spot plate Add about 2 drops of Iodine Solution Wait up to 30 seconds for a colour change

The Test for STARCH The colours black, dark purple, or dark blue indicate starch is present

The Test for STARCH The colours brown, yellow, or not changed, mean that there is no starch

Test for Reducing Sugars

Test for Reducing Sugars Note: Glucose is a reducing sugar, so we use this as a test for glucose.

Test for Reducing Sugars This test requires heating in a water bath, at 40oC to 50oC for 5 minutes.

Test for Reducing Sugars This test requires heating in a water bath, at 40oC to 50oC for 5 minutes. The reagent used is called Benedict’s Solution.

Test for Reducing Sugars Place about 5 mL of the unknown solution in a test tube.

Test for Reducing Sugars Place about 5 mL of the unknown solution in a test tube. Add about 10 drops of Benedict’s Solution.

Test for Reducing Sugars Place about 5 mL of the unknown solution in a test tube. Add about 10 drops of Benedict’s Solution. Place the test tube in a water bath, at a temperature between 40oC and 50oC for 5 minutes

Test for Reducing Sugars If the solution turns orange after heating, the result is positive, and glucose is present.

Test for Reducing Sugars Other shades of orange or yellow can also mean that reducing sugars are present.

Test for Reducing Sugars If the solution stays blue after heating, the result is negative, and glucose is absent.

Test for Reducing Sugars A green or brownish colour can result if traces of glucose are present.

Test for Reducing Sugars A green or brownish colour can result if traces of glucose are present. (‘traces’ means very small amounts)

This is a molecule of albumin, the protein in egg white Test for Protein This is a molecule of albumin, the protein in egg white

Test for Protein The test for protein does not require heating, and so, could be performed either in a test tube, or on a spot plate.

Test for Protein The test for protein does not require heating, and so, could be performed either in a test tube, or on a spot plate. In this presentation, we shall use test tubes. You may use spot plates in the lab.

Test for Protein Place about 5mL of the unknown solution in a test tube.

Test for Protein Place about 5mL of the unknown solution in a test tube. Add about 10 drops of Biuret Reagent.

Test for Protein Place about 5mL of the unknown solution in a test tube. Add about 10 drops of Biuret Reagent. Mix and look for a colour change.

different positive results Test for Protein If the solution becomes purple, violet, or lavender, it means that protein was present. different positive results

Test for Protein If the solution stays pale blue, it means that there was no protein in the sample. Negative result

Test for Fat

Test for Fat Often called the grease spot test…. Bag of churros Bag of samosas Greasy French Fries

Test for Fat Often called the grease spot test…. Fat of any type will make paper translucent (light shows through), without drying up.

Test for Fat Often called the grease spot test…. Simple, yet effective!

Let’s recap:

Let’s Recap: Starch Test:

Let’s Recap: Starch Test: iodine turns from brown to black

Let’s Recap: Starch Test: Glucose Test: iodine turns from brown to black Glucose Test:

Let’s Recap: Starch Test: Glucose Test: iodine turns from brown to black Glucose Test: benedict’s turns from blue to orange with gentle heating (50oC)

Let’s Recap: Starch Test: Glucose Test: Protein Test: iodine turns from brown to black Glucose Test: benedict’s turns from blue to orange with gentle heating (50oC) Protein Test:

Let’s Recap: Starch Test: Glucose Test: Protein Test: iodine turns from brown to black Glucose Test: benedict’s turns from blue to orange with gentle heating (50oC) Protein Test: biuret turns from blue to violet

Let’s Recap And Finally Fat... The Grease Spot...

Now you are all expert nutrient testers. Next, The Lab!