Purple Power
The Color Purple is in, from Broadway to the produce aisle. Asparagus, potatoes, broccoli and tomatoes are just a few of the latest produce items with a deep violet hue showing up in grocery stores and nurseries. While purple produce may raise eyebrows, it also provides added compounds that research has associated with preventing heart disease and certain cancers.
Spurring the developments of red-blue fruits and veggies are scientists from both the private and public sectors. With these eye-catching foods, researchers are looking to increase Americans' fruit and vegetable intake through novelty, distinct taste, or added health benefits.
Research in Color
| Anthocyanins are sensitive to acidity; changes in acidity (pH) cause the compounds to alter their structure. In acids the substances turn red and in bases they look blue. To make your own pH indicator, you can use the anthocyanins in purple cabbage. |
Colors indicate certain plant compounds, and the dark red-blue to purple color screams anthocyanins. Anthocyanins, from the Greek words anthos meaning flower and kyanos meaning blue, are a group of phytochemicals (compounds that occur naturally in plants) in the flavonoid family. Many flavonoids give fruits and vegetables their distinct colors.
Studies have found that anthocyanins (pronounced an-tho-SIGH-uh-nins) are powerful antioxidants. Antioxidants are compounds that can bind to and neutralize highly reactive free radicals that can lead to diseases such as cancer.
As a general rule, the more pervasive and deeper the blue-red color, the higher the level of anthocyanins. Blueberries and cherries, for example, are rich in anthocyanins, while bananas contain relatively low amounts. (Not to malign the banana, which is a good source of potassium and vitamin C.)
It’s in the Breeding
To increase the anthocyanin level in fruits and vegetables, scientists employ traditional breeding techniques and a lot of travel. In order to heighten the anthocyanin-producing genes by crossbreeding
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Photo courtesy of Institute for Culinary Arts, MCC |
researchers first need to find foods with those genes. Conventional-colored fruits and vegetables in this country often have purple ancestors or distant cousins in other parts of the world.
Take the carrot. In the Roman era, purple and white carrots were a typical sight. By the 10th century, carrots were reportedly grown in Afghanistan and Pakistan, the purple soon joined by red, green, and black strains. It was only in the 15th or 16th century that the Dutch bred the orange carrot, in support of the House of Orange and its struggle for Dutch independence. (To read more carrot history and fun facts visit a virtual carrot museum, where you can also explore an actual museum dedicated to carrots.)
The purple tomato reportedly traces its roots back to a wild species in South America that is poisonous.
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Photo courtesy of Oregon State University Dept. of Horticulture |
Crossbreeding produced an edible strain and researchers say an anthocyanin-rich eggplant-colored tomato could come to market within the next few years. Purple asparagus was developed in Italy hundreds of years ago; purple potatoes are common in Peru.
Genetics also promise to play an increasing role in traditional breeding programs as scientists identify more phytochemical-producing genes. In November, researchers announced they located the gene in apples that controls anthocyanin production, which gives apples their red appearance. This information can be used to pinpoint which anthocyanin-containing apples to breed. Researchers have already identified a number of anthocyanin-related genes in other fruits and vegetables.
What’s It Doing in There?
Part of the challenge in developing produce with additional natural compounds is ensuring the fruits and vegetables go beyond their intriguing looks. There is taste and yield to consider. Researchers also need to test that the produce contains higher levels of anthocyanins and that the body can absorb them.
Scientists are only beginning to study anthocyanin-rich fruits and vegetables. Early research has yielded positive findings. Studies have shown that the more reds and blues in a potato, the higher its antioxidant level. A study published last month in the British Journal of Nutrition found that laboratory rats fed anthocyanin-rich purple potato flakes showed significantly higher antioxidant activity than rats fed cornstarch.
Another challenge lies in ensuring the anthocyanins remain chemically stable. For example, preparation of anthocyanin-heightened foods can cause the phytochemical to break down. Along with pH sensitivity, anthocyanins are water soluble. Boil purple asparagus too much and it will turn green. (Adding acids, such as lemon juice, will help the asparagus retain its anthocyanins.)
| Anthocyanins are also gaining in popularity as a natural food dye. For years, food manufacturers have used synthetic substances to pump color into conventional foods. Think bright yellow butter and green ketchup. Organic companies can only use natural substances to dye food items. Now, with a heightened interest in organic, natural, and healthful foods, manufacturers are increasingly turning to natural pigments to produce foods with a twisted color. |
A Palette of Health
Anthocyanins are only one of many groups of phytochemicals that researchers are using to enhance or alter
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Photo courtesy of Oregon State University Dept. |
the color of produce. There is, for example, a virtual rainbow of carrots available to the gardener - not only purple, but red, blue, yellow and white. Red carrots have increased levels of lycopene, a phytochemical found in tomatoes and associated with lower risks of prostate and breast cancers among other health benefits. Yellow carrots contain more xanthophylls, a substance found in plants’ leaves and related to eye health.
Indeed, while purple fruits and vegetables can add visual zip and cancer-protective compounds to your menu, research has shown that people need a wide assortment of phytochemicals to provide good health. After all, the conventional carrot is packed with carotene, a compound that provides its orange color and is associated with lowering cancer risk. So, by all means, enjoy a little purple cauliflower or potatoes, but be sure to include a helping of those traditional greens, yellows, and oranges for a colorful health boost.
This is the first in an occasional series of articles on Weird Foods.
The American Institute for Cancer Research (AICR) is the only major cancer charity focusing exclusively on the link between diet, nutrition and cancer. The Institute provides a wide range of consumer education programs that help millions of Americans learn to make changes for lower cancer risk. AICR also supports innovative research in cancer prevention and treatment at universities, hospitals, and research centers across the U.S. The Institute has provided more than $70 million in funding for research in diet, nutrition and cancer. Visit the AICR Web site. AICR is a member of the World Cancer Research Fund International.
