What Foods are the Best Source of Vitamin C?

Vitamins and Nutrition

A vitamin is a naturally occurring chemical that is required for life by humans but is not made in their own bodies. Vitamins are nutrients which must be taken in as part of a healthy diet. Although humans cannot make most of the vitamins (humans can make vitamin D!) bacteria can. Therefore, vitamins move up the food chain and are ultimately consumed by humans as either meat, vegetables, fruits, dairy products, or grains. There are many types of different vitamins, each with its own purpose. Many vitamins help enzymes to complete their jobs in the body. Vitamins such as the vitamin B complex are essential to the enzymes in the body that assist the metabolism of foodstuffs such as carbohydrates and fats. Some vitamins also act as hormones. Vitamin A is a hormone that regulates growth in the cell and vitamin D is a hormone that regulates bone growth.

There are two major groups of vitamins that are essential in the diet, water soluble vitamins and fat soluble vitamins. Water soluble vitamins are easily dissolved in water and can be found in the juices or extracts of foods. Although water soluble vitamins are readily found in the diet and can easily be obtained from vitamin pills, most water soluble vitamins cannot be stored in the body. Water soluble vitamins eaten in excess of dietary needs will be lost in the urine. Fat soluble vitamins are found in the fat or oils of many foodstuffs. The fat soluble vitamins are easily stored by the body which can result in health problems if too much of any fat soluble vitamin is taken in. In many cases, people who have taken in megadoses of the fat soluble vitamins have caused serious health problems rather than benefits.

Vitamin C

Vitamin C is a water soluble vitamin found abundantly in many plants. Vitamin C is essential to growth in the human body because it is required for making collagen. Collagen is a structural protein which provides much of the framework in the cell, just as the skeleton provides the framework for the body. If your diet is deficient in vitamin C, the cells in your body may begin to stop growing or even die. The disease that results from a severe deficiency in vitamin C is called scurvy. People with scurvy get bruises easily because their blood vessels are very weak. Their skin and teeth become very unhealthy also. In the old days, sailors often got scurvy while at sea because their diets had little or no fresh fruits or vegetables. Some sailors found that they could prevent scurvy by eating citrus fruits like oranges, lemons, or limes. (That is why sailors are nicknamed limeys.)

What foods have the most vitamin C?

In this laboratory we will investigate which foods have the most vitamin C. Because vitamin C is a water soluble vitamin we can determine the amount of vitamin C in the food by making a water extract from the food. Factors such as length of storage, and exposure to heat, light, and oxygen affect the amounts of many vitamins in food. Chemists at food companies add preservatives to food to not only protect the taste but also to protect the nutrient value of the food. We will also investigate the effect of these environmental factors on the amounts of vitamin C in the food. Since vitamin C is water soluble, boiling vegetables in water to cook them may affect their nutrient value. Can you design an experiment to test that hypothesis?

Experimental Procedure

In this laboratory we will measure the amount of vitamin C in many different types of foods. The chemical reaction we will use to measure the amount of vitamin C uses one of its functions in the body. Vitamin C (also called ascorbic acid) participates in chemical reactions in your cells oxidation-reduction reactions. Because of its function, vitamin C can react with iodine. We will measure the amount of vitamin C by adding iodine to our food extracts until the vitamin C can bind no more iodine. Iodine in excess of the vitamin C will react with a starch solution you will add to the extract to produce a bluish-black color. The stepwise addition of a chemical (like iodine in this experiment) to measure another chemical such as vitamin C is called a titration. To make the measurement of the iodine added easier for you, we will be using a measuring device called a burette. You will use the stopcock on the burette to slowly add iodine one milliliter (ml) at a time.

Materials you will need:

Food sources of vitamin C:

Various juices. (30 ml)
Various plants, flowers, fruits, grains, and vegetables.
Vitamin C tablet.
Ascorbic acid solution. (0.1 g in 100 ml H₂O)
Starch solution (1%)

Mix 1 g starch in 100 ml boiling H₂O.
Boil for one minute while stirring.
Stir until completely dissolved (this solution will be cloudy).
Iodine solution
Mix 0.6 g potassium iodide in 500 ml H₂O.
Mix 0.6 g iodine in 50 ml of ethyl alcohol.
These two iodine solutions should be mixed well before combining.
Combine the two iodine solutions and add an additional 450 ml of H₂O.
1 Molar Hydrochloric Acid (HCl), (5 ml)
Buret (1 per group)
Distilled water. (whenever water is indicated use this distilled water)
100 ml Graduated cylinder.(1)
250 ml Erlenmeyer flask or 250 ml beaker.(1 per group)
Funnel.(1 per group)
Something to strain out the plant pulp: Glass wool, cheesecloth, nylon screen door mesh, or strainer
10 ml Pipette & Pipetter.(1 each)
100 ml Beaker.(1 per group)
Blender

Procedure:

Measuring vitamin C content of ascorbic acid:
- Place 30 ml of the Ascorbic acid solution in a 250 ml flask or beaker.
- Add 2 drops of the 0.1 M hydrochloric acid to the flask. Be careful the acid can burn skin and eyes.
- Add 5 ml of the starch solution to the flask.
- Fill a buret with the iodine solution. Record the initial volume reading.
- Using the stopcock at the bottom of the buret, add the iodine solution in 1 ml increments to the flask while swirling the flask. Add iodine until the solution stays blue-black for 15 seconds.
- Record the volume reading on the buret. If you began at 0.00, the volume you read on the buret will be the volume of iodine solution you have added to the flask.
Preparing the vitamin C extracts:
- Chop food material into small pieces and place into blender. (be creative and try different kinds of materials from different food groups).
- Add 100 ml of water to the blender.
- Blend using the highest speed until the material is throughly ground.
- Strain the ground extract using cheesecloth (a strainer or glass wool works well also)
- Measure 30 ml of the strained extract into a 250 ml erlenmeyer flask or beaker.
Measuring vitamin C in the food or juice:
- Place 30 mL of the food extract solution in a 250 ml flask or beaker.
- Add 2 drops of the 0.1 M HCl to the flask.
- Add 5 ml of the starch solution to the flask.
- Fill a buret with the iodine solution. Record the initial volume reading.
- Using the stopcock at the bottom of the buret, add the iodine solution in 1 ml increments to the flask while swirling the flask. Add iodine until the solution stays blue-black for 15 seconds.
- Record the volume reading on the buret. If you began at 0.00, the volume you read on the buret will be the volume of iodine solution you have added to the flask.
Cooking and Vitamin C
Does the way you prepare your food affect the vitamin C available to be ingested? Vitamin C is a water-soluble vitamin. Would cooking food by boiling in water affect the vitamin C content? If vitamin C is lost during the cooking process, where does it go? What types of experiments could you design to test your hypothesis? You will be testing your hypothesis to determine if vitamin C content is changed during cooking or if different ways of food preparation yield different amounts of vitamin C.

Preparing the food vitamin C extracts:
- Obtain green beans prepared using several cooking methods (Green beans is just an idea for a vegetable which can be obtained fresh, frozen and canned. However any vegetable or fruit could be used.)
- Chop food material into small pieces and place into blender.
- Add 100 ml of H₂O to the blender.
- Blend using the highest speed until the material is thoroughly ground.
- Fill a buret with the iodine solution. Record the initial volume reading.
- Using the stopcock at the bottom of the buret, add the iodine solution in 1ml increments to the flask while swirling the flask. Add iodine until the solution stays blue-black for 15 seconds.
- Record the volume reading on the buret. If you began at 0.00, the volume you read on the buret will be the volume of iodine solution you have added to the flask.
- Compare the relative amounts of ascorbic acid present in the samples you are testing. Compare your results with those of other members of the class. What do the results show?
Questions:
- What juices or drinks had the most vitamin C?
- Did the drinks have the vitamin C that they advertised on the labels?
- What food sources had the most vitamin C?
- What families or groups had the most vitamin C?
- Did plants that you don't normally eat have vitamin C?
- Did heat affect the vitamin C content of food?
- Did heat increase or decrease the vitamin C levels?
- What way of food preparation would be the most nutritious?
- Do you have any ideas now to get more vitamins from your meals?
When you have completed your experiment, you might want to check out the Dole Pineapple Co. Web site for information about vitamin C content in fruits and vegetables.
Last updated on July 28, 1998