Cooking can alter a food's vitamin C content | Science News for Students

Cooking can alter a food's vitamin C content

Inspired by history class, a teen boils bell peppers for science
Jun 1, 2017 — 11:50 am EST
green pepper

Green bell peppers are eaten both raw and cooked. A teen decided to find out if cooking altered the food’s vitamin C content.


LOS ANGELES, Calif. — Pirates were scurvy scallywags. But it was the “scurvy” — a condition caused by lack of vitamin C — that inspired 14-year-old Amber Cui. A lesson in history class about how pirates suffered from scurvy led this freshman from Cookeville High School in Tennessee to study the vitamin C content of green peppers as a science project. She found that vitamin C content is highest when peppers are fresh. Boiling brings the concentration down. But the vitamin's level will rise again if boiling goes on long enough.  

Also known as ascorbic acid, vitamin C is one of the many nutrients found in fresh fruits and vegetables. The U.S. National Institutes of Health notes that teen boys should get 75 milligrams (0.002 ounce) and teen girls should get 65 milligrams (also around 0.002 ounce) of vitamin C each day. The vitamin is important for making collagen — a protein found in cartilage and bone.

People who do not get enough of vitamin C may feel tired. Their legs may hurt. Their gums may begin to bleed — even fall out. These are the symptoms of scurvy. In the 1800s, pirates and other sailors often spent long times at sea without access to good sources of vitamin C, such as fresh fruit or vegetables. That's why many developed scurvy.

Pirates may be the stuff of Disney movies now, but scurvy hasn’t gone away. Even today, Amber notes, “some people can’t get enough vitamin C.” Scurvy can still appear after famines, for example, or even among people who just don’t eat enough fruit and veggies. While looking for more information about scurvy, the teen saw some dietary guidelines that recommended eating vitamin-C-rich fruits and vegetables raw. Amber hates raw green peppers, but doesn’t mind them cooked. So she began to wonder what cooking does to vitamin C levels of veggies.

When fresh, 340 grams (one cup) of green bell peppers have about 129 milligrams (0.005 ounce) of vitamin C. To find out how cooking might change that, Amber chopped up four green peppers and weighed each piece. She kept one pepper’s pieces fresh. She put another pepper in boiling water for 10 minutes, boiled a third for 20 minutes and a fourth for 30 minutes. (After 30 minutes of boiling, she notes, that last pepper “didn’t smell the best.”)

Amber then placed each pepper in a blender and used a strainer to separate the liquid from the solid bits. The teen tested the liquid using a vitamin C test kit that she bought online. By adding the pepper juice drop by drop to her testing kit, she was able to determine the concentration of vitamin C in each pepper.

blended peppers
Yum. Amber blended and strained her bell peppers to measure how much vitamin C they contained.
A. Cui

Raw peppers indeed had the most vitamin C, she found. Ten minutes of boiling reduced the vitamin C level by about 25 percent. But as the peppers boiled for 20 or 30 minutes, she says, the vitamin C level began to rise again. This might be because after boiling for that long, the peppers begin to lose water. That could concentrate the vitamin in the vegetable.

Amber brought the results of her cooking chemistry here to the Intel International Science and Engineering Fair (ISEF). Created by Society for Science & the Public and sponsored by Intel, the yearly fair now draws almost 1,800 high school students from more than 75 countries to show off their research. (The Society also publishes Science News for Students and this blog.)

Most people probably don’t blend their peppers before they eat them. But we do chew and digest them. That’s how the body is able to crack into the hard cell walls of plants to access their vitamins, notes Anitra Carr. She studies the health effects of vitamin C at the University of Otago in Christchurch, New Zealand.

Amber’s pepper results are similar to other scientific findings, Carr says. “The amount of vitamin C in foods generally decreases with cooking,” she notes. The vitamin can leach out into the water in which peppers are cooked. Heat and other chemical processes also can break it down.

But we might still get more vitamin C from some cooked vegetables than raw, Carr says. How? Cooking or blending can soften and break up plant cell walls, she explains. This can make it easier for the body to use the vitamins inside. Some of those vitamins can stay locked within raw vegetables if chewing and digesting doesn’t break up enough cell walls. But it depends on what the vegetable is, how it’s cooked and how much is eaten. “In other words, it is difficult to know exactly how much will be taken up from different foods unless blood vitamin-C levels are tested,” Carr says.

Amber is interested in looking at how different kinds of cooking might change the nutrients inside fruits and vegetables. But so far, her experiments haven’t changed her views on bell peppers. “I can’t eat them raw,” she says. “I like the crunch. I just don’t like the taste.”

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Power Words

(more about Power Words)

cartilage     A type of strong connective tissue often found in joints, the nose and ear. In certain primitive fishes, such as sharks and rays, cartilage provides an internal structure — or skeleton — for their bodies.

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.

collagen     A fibrous protein found in bones, cartilage, tendons and other connective tissues.

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.

engineering     The field of research that uses math and science to solve practical problems.

fruit     A seed-containing reproductive organ in a plant.

high school     A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.

Intel International Science and Engineering Fair     Or Intel ISEF. Initially launched in 1950, this competition is one of three created (and still run) by the Society for Science & the Public. Each year, approximately 1,800 high school students from more than 75 countries, regions, and territories are awarded the opportunity to showcase their independent research at Intel ISEF and compete for an average of $4 million in prizes. 

internet     An electronic communications network. It allows computers anywhere in the world to link into other networks to find information, download files and share data (including pictures).

liquid     A material that flows freely but keeps a constant volume, like water or oil.

National Institutes of Health     (or NIH) This is the largest biomedical research organization in the world. A part of the U.S. government, it consists of 21 separate institutes — such as the National Cancer Institute and the National Human Genome Research Institute — and six additional centers. Most are located on a 300 acre facility in Bethesda, Md., a campus containing 75 buildings. The institutes employ nearly 6,000 scientists and provide research funding to more than 300,000 additional researchers working at more than 2,500 other institutions around the world.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

Society for Science & the Public  A nonprofit organization created in 1921 and based in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: the Regeneron Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).

symptom     A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

taste     One of the basic properties the body uses to sense its environment, especially foods, using receptors (taste buds) on the tongue (and some other organs).

vitamin     Any of a group of chemicals that are essential for normal growth and nutrition and are required in small quantities in the diet because either they cannot be made by the body or the body cannot easily make them in sufficient amounts to support health.


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