- Ipomoea batatas
- Lutein, Beta-carotene, Chlorogenic acid, Anthocyanin
Natural Antiangiogenic Molecules:
The sweet potato is a tuber (edible storage root) belonging to the Morning Glory family, and is actually not related to a potato as the name implies. Sweet potato is also often confused with the yam, which is a completely different plant, a tuber related to lilies that grows from a vine, and which grows to much larger sizes.
Sweet potatoes have a smooth skin and usually are elongated with tapered ends. Their colors range from purple, violet, orange or grey and flesh that can vary from white to various orange hues. In contrast, yams are West African in origin (their name comes from "njam" which means "to eat") and are different in appearance, with tree bark-like rough thick skin brown or black in color, and flesh that is never orange and is more starchy than sweet potato. Anti-angiogenic carotenoids are high in sweet potatoes while very low in yams.
The sweet potato originated in Peru, Ecuador, and Venezuela, and was brought to Polynesia as early as 1000 AD by maritime travelers. Settlers found Native Americans in Louisiana eating sweet potatoes. The tuber was first brought to Europby Christopher Columbus. Today, it is one of the most important root vegetables in the world. It is a staple crop in Papua New Guinea, the Solomon Islands, Burundi, Rwanda, and Uganda. Eighty percent of the world's sweet potatoes are grown in China, mainly for livestock feed, while the Americas grow less than 3% of the world's supply. Europe has only a small sweet potato production, located in Portugal.
Sweet potatoes are a warm season plant, sown by stem or root cuttings rather than by seeds. They are sensitive to cold temperature and tubers are harvested before the first frost. Sweet potatoes are often "cured" in a process that improves storage, involving drying the freshly dug roots on the ground for 3 hours, followed by storage in warm, humid conditions for 5-14 days. Such cured sweet potatoes can be kept for 13 months at 55-59° F.
There are over 6,500 varieties of sweet potatoes worldwide. See a gallery of sweet potato varieties at Saveur.com. The Beauregard, is the most common variety in U.S. supermarkets; it has a reddish-orange skin and bright orange flesh. Other popular varieties include the Carolina Ruby, which has purple-gray skin and dark orange flesh and is excellent for bakingJewel, which is copper-skinned and orange-fleshed and keeps moist when baked; Red Garnet is considered most savory with a loose texture. Non-traditional varieties include the Japanese White with a chestnut flavor and velvet texture; the Batata with a grey hue and the Okinawa with a purple tint. The Maori potato, or Ureniki variety is a purple sweet potato that were consumed by New Zealand settlers of Polynesian descent as early as the early 1900s. A cream-fleshed variety called boniato is popular in the Caribbean.
Sweet potatoes are one of the easiest vegetables to cook. They can be steamed or roasted in their skins, or they can be mashed, pureed, fried or baked. They can also be candied, canned or dried as chips. The flavor of sweet potato pairs well with many spices and condiments including cinnamon, honey, nutmeg, ginger and lime. Common sweet potato dishes in the United States include sweet potato pie, sweet potato casserole and sweet potato fries. Sweet potato is prevalent in Asian dishes, ranging from the simple street snack of roasted sweet potato to its popular use in Japanese tempura to Chinese tong sui which is a sweet potato soup flavored with sugar and ginger.
Root vegetables like sweet potatoes can be found next to potatoes in the grocery store. Choose sweet potatoes that are firm with intact skin and no bruises. Sweet potatoes can be stored in a dry and cool (55-60° F) environment for one month. If dry cured (exposed to temperatures around 86 F for several days), they can last in storage throughout the winter. Avoid storing them in the refrigerator or at temperatures below 55° F since sweet potatoes can develop “hardcore”, where the root center remains tough, even upon cooking. Cooked sweet potatoes can be stored in the refrigerator for 5 days.
Sweet potatoes develop sweetness during cooking. Upon heating, the enzyme amylase in sweet potatoes converts starch molecules into the sugar maltose, which is one third as sweet as table sugar (sucrose). Some sweet potato varieties are more moist and sweet based on starch to maltose conversion– which can be as high as 75%. Because amylase is most active at 135 – 170° F but deactivated at higher temperatures, it is best to slow-bake sweet potatoes rather than to quickly boil or microwave them, in order to maximize their sweetness.
Sweet potatoes contain a variety of natural molecules that have anti-angiogenesis mechanisms of cancer prevention. These micronutrients include carotenoids (lutein and beta-carotene), polyphenols (chlorogenic acid) and flavonoids (anthocyanin).
Lutein is a natural yellow-colored carotenoid synthesized by plants to quench activated overproduced chlorophyll from photosynthesis. In experimental animals bearing breast cancer cells, dietary lutein at 0.002% was been shown to inhibit tumor angiogenesis, and result in tumors that were 40% smaller in size. Beta-carotene is a natural red-orange pigment that inhibits the proliferation, migration, and tube formation of blood vessel endothelial cells in laboratory studies. Beta-carotene supplements given to volunteers resulted in reduction of the lymphangiogenesis growth factor VEGF-D circulating in their blood serum of male smokers. Chlorogenic acid is a polyphenol found in sweet potatoes that is highest in purple-fleshed varieties and lowest for white-fleshed varieties. In an animal model of laser-induced choroidal neovascularization (CNV) of the eye, systemically-administered chlorogenic acid reduced CNV size seen by angiography, possibly through inhibition of the enzyme MMP-9. Purple sweet potato varieties also contain anthocyanin pigments, which are anti-angiogenic flavonoids that suppress vascular endothelial growth factor (VEGF) and reduce tumor cell proliferation in laboratory studies. Of note, although anthocyanins are present in the skin of orange- or yellow-fleshed cultivars, none are found in the flesh.
Epidemiological evidence suggests that sweet potatoes, with their anti-angiogenic pigments (including anthocyanin and carotenoids), may prove an important part of a chemopreventive diet. In the NIH-AARP Diet and Health Study, which enrolled almost half, a million people, researchers found that men who regularly consumed sweet potatoes had lower rates of lung cancer than those who did not. Among former smokers, men who consumed sweet potatoes had a 14% reduced risk of lung cancer. Another study in the International Journal of Cancer found that premenopausal women who consumed large amounts of sweet potatoes and other carotenoid-rich fruits and vegetables had a 20% lower risk of breast cancer compared with those who consumed the least. A study of women in Iowa revealed that individuals who ate sweet potatoes every day or every other day had a 28% reduced risk of developed Non-Hodgkin’s Lymphoma.