Carotenoid Lab

Introduction:

Carotenoids are responsible for the yellow, orange, and red colors found in fruits and vegetables. They absorb light in the ultraviolet and visible light region of the spectrum, thus, making it possible for the absorption of light to be measured. Most of the carotenoids absorb in the blue region (430-500 nm).

The name carotenoid is derived from Beta-carotene. Carotenoids are divided into two groups: hydrocarbons and xanthophylls. Physically carotenoids are lipids and are therefore soluble in other lipids and in fat solvents such as acetone, alcohol, diethyl ether, and chloroform.

Carotenoids act as antioxidants and some can be converted to vitamin A in the body once digested. Vitamin A is necessary for vision, and cell growth differentiation. One of the best ways to obtain the daily-recommended value of vitamin A is in the consumption of vegetables such as carrots, sweet potatoes, and spinach. It has been found that the canning process does not affect the amount of carotenoids found in fruits and vegetables.

Background for Teachers:

This lab does require the use of solvents. Thus, there are some steps that you may want to do rather than letting the students for safety reasons.

In this lab you may want to try other vegetables that are not high in vitamin A so that students can compare the values obtained. (Example: green beans)

Materials:

Blender
Vegetable (carrots, sweet potato, peppers, or spinach)
Ethanol in squirt bottle
Electronic scale
Graduated cylinder
Funnel and miracloth or filter paper
Spectrophotometer 20

Procedures:

  1. Homogenize the vegetable as fine as possible with the blender.
  2. Mass 5 g of the vegetable and place in a 100 ml graduated cylinder.
  3. Add enough ethanol to cover the vegetable plus 1-inch.
  4. Blend the vegetable and ethanol until the mixture is liquefied.
  5. Pour the liquefied mixture into a funnel lined with miracloth or filter paper.
  6. Rinse the homogenate with ethanol using a squirt bottle until no color remains. The fitrate should be collected into a 100 ml graduated cylinder.
  7. After all the pigments have been removed fill the graduated cylinder with ethanol until the level is brought to 50 or 100 ml. Record the level that you brought the ethanol to.
  8. Turn the spectrophotometer on and set the wavelength to 470nm. Then place a blank test tube in the spectrophotometer and zero the absorbance.
  9. After the spectrophotometer is zero place the carotenoid solution in the test tube and record the absorbance.

Calculations:

Total carotenoid in sample = ( Absorbance) (volume) (10 6 )
Total carotenoid in sample = (2500) (100) (grams of vegetable)

Results:

Vegetable Total carotenoid
   
   

Questions:

  1. Which vegetable contained the highest total carotenoid content?



  2. Why is it important for you to consume fruits and vegetables that are high in carotenoids?



Reference:

Gross, Jeana. Pigments in Vegetable Chlorophylls and Carotenoids. Van Nostrand Reinhold. New York. 1991.

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