Lab: Testing Foods for Nutrients

Background:

Substances in food that can be used by an organism for energy or for growth and repair are called ______. Nutrients include______, ______, ____, minerals, and vitamins. Cells of all organisms are composed of these nutrients and water. There are several chemical tests that can be used to determine which nutrients, if any, are present in a substance. You will use some of these tests in the activity.

Purpose:

1. Learn how to test substances for the presence of carbohydrates, proteins, and fats.

2. Perform nutrient tests on several foods to determine which nutrients are present.

Hypothesis:

If is tested for nutrients, then the indicators will test positive for the following nutrients: .

Materials:

5 foods

cereal, cheese, beans, apple, potatoes

mortar/ pestle Test tubes stirring rods

Hot water bath Spotting Trays

Pipettes brown paper bags

Prodcedure:

Part A: CLASS DEMO – We will do this section together.

1. To observe a negative test (control), water will be used with each nutrient indicator.

2. To observe a positive test, known substances containing the nutrient will be used.

3. Note all color changes in Table 1.

Part B: TESTING FOOD ITEMS

* Begin by labeling 5 test tubes (for the simple sugar test) with labeling tape. Write the food

names and your initials. (Place tape high on the test tube so it won’t be submerged in the water bath.)

1. Choose a food item to test. You only need a small amount.

2. Grind the food thoroughly using the mortar and pestle.

3. Take a small amount of sample & perform the LIPID TEST (brown paper bag) BEFORE ADDING H2O!

4. Add water to the remaining ground food (about 1/2 way up the mortar), and continue to grind

(this releases the nutrient into the water, so be sure to do this thoroughly) (The food mixture should be dilute – not thick.)

5. Using a pipette, add about one pipette full of the sample to the appropriately labeled test tube.

*DO NOT ADD THE FOOD TO THE TEST TUBE – JUST THE LIQUID!

6. Add ½ pipette of water to the test tube already containing the nutrient mixture.

7. Using a spoon, distribute the rest of the food sample into 2 spot plate wells.

Now the food is properly prepared and ready to be tested with the indicators. Follow the procedures below.

8. Thoroughly clean the mortar & pestle after each food test. Dispose of used pipettes.

(Improper cleaning may cause contamination of the next sample.)

9. Repeat procedure above for all food items.

Data:

TABLE 1: NEGATIVE & POSITIVE TESTS USING NUTRIENT INDICATORS

Substance Tested / Nutrient / Indicator / Negative test (-)
(Using water as a control) / Positive test (+)
(Color change when nutrient present)
/

SUGAR

/ Benedict’s Solution
(must use hot water bath)
STARCH / Iodine Solution
PROTEIN / Biuret’s Solution
LIPID / Brown Bag

* Note: A food is + for a nutrient only if it has the + test color. Any other color is negative.

Remember there will be food particles in your test samples, so make careful observations! If you’re unsure about a certain color, test it again (make a more dilute sample so that any color changes are easier to see).

TABLE 2: ______

FOOD ITEM / Color for LIPID Test
(translucent/ opaque) / Lipid Test
(+/-) / Color
for SUGAR Test / SUGAR
Test
(+/-) / Color for STARCH Test / Starch Test
(+/-) / Color for PROTEIN Test / Protein Test
(+/-)

KEY:

- = negative test (nutrient NOT present);

+ = positive test (nutrient present)

+/- = slightly positive (evidence of a small amount of nutrient)

Analysis and Conclusion:

Research: Use the following website to determine the nutrients found in each of the foods you tested: http://nutritiondata.com/ . Enter the food names as you see them in Table 3 below.

*Be sure to toggle to 1 ounce (28 grams) above the food label so that the same mass of each food is being compared!*

If the amount is less than 1 gram – indicate ZERO for that nutrient!

(Keep in mind that our indicators may need a certain amount of nutrient to even be detected!)

*Note – To get the number of complex carbs:

Total carbs (g) – sugars (g) – fiber (g) = Complex carbs (g)

Table 3: ______

Food Item / Reported Nutrients
Cheerios
(28 grams) / ____g complex carbs, ___ g fiber ____ g sugar, ____ g fat , ____g protein
Mozzarella Cheese – whole milk
(28 grams) / ____g complex carbs, ___ g fiber ____ g sugar, ____ g fat , ____g protein
White Beans – matured, canned
(28 grams) / ___g complex carbs, ___ g fiber ____ g sugar, ____ g fat , ____g protein
Apple –
raw, without skin
(28 grams) / ____g complex carbs, ___ g fiber ____ g sugar, ____ g fat , ____g protein
Microwaved Potato, cooked in skin, flesh, without salt
(28 grams) / ____g complex carbs, ___ g fiber ____ g sugar, ____ g fat , ____g protein

Conclusion Questions

1. a. Provide reasonable explanations for any of your results that did not match the reported nutrients contained in each food. (Don’t just tell me that you didn’t clean the materials well! That is careless!)

b. Did your results match your hypothesis? If there were differences, explain what you learned about that food.

2. Fiber is listed as a carbohydrate, but does not provide any calories or energy.

What is fiber and why is it still required in our daily diets?

3. What were the controls in this experiment? Why was water also used?

4. List 3 inorganic minerals and describe how they are important to living things. (Be specific about their functions.)