The Sweet Potato

Sweet potato lined up. Pink skinned and presumably pink fleshed too.
Photo by Aunt Masako, c/o Pixabay.

The sweet potato (Ipomea batatas {L.} Lam.) is now a regular feature of the grocer’s retailing shelves. The tubers which are swollen roots are available in orange, purple and actually many colours in between (white through to almost black) it has attracted a great deal of attention over many years because of its high vitamin A content. Not only are the tubers eaten, but the leaves also contribute plenty of nutritional value.

Originally, the sweet potato was found in Mexico but has been grown commercially in a number of countries which can offer the right growing conditions. The USA, Japan and most parts of the Far East, Australia and Oceania, sub-Saharan Africa, and parts of southern Europe are ideal for commercial production. The crop is now the sixth largest crop in the world.

Cooking With Sweet Potato

A root which is highly versatile. It can be roasted and baked, fried or barbecued. It also makes a good base for soups and stews in combination with pumpkin, squashes and ordinary potatoes. Some chefs like to boil the tuber before mashing to a pulp or pureeing. They make excellent vegetarian fillings for quesadillas and falafels. In the USA, it is a traditional dish to add a syrup such as maple syrup to really sweeten them up. They almost become dessert like.

leave the skin on when baking or frying them. It is especially important it seems when preparing vegetable crisps. Peeling a sweet potato will cause discolouration. Keep them soaked in cold water until you are ready to use them in a dish. We prepare fries and wedges with them

Nutritional Value Of Sweet Potatoes 

Nutrition Facts
Amount Per
Calories 86
% Daily Value*
Total Fat 0.1 g0%
Saturated fat 0 g0%
Polyunsaturated fat 0 g
Monounsaturated fat 0 g
Cholesterol 0 mg0%
Sodium 55 mg2%
Potassium 337 mg9%
Total Carbohydrate 20 g6%
Dietary fiber 3 g12%
Sugar 4.2 g
Protein 1.6 g3%
Vitamin A283%Vitamin C4%
Calcium3%Iron3%
Vitamin D0%Vitamin B-610%
Cobalamin0%Magnesium6%
*Per cent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.

The sweet potato is grown as a staple  but also contains a number of phytochemicals with active health benefits (Bovell-Benjamin, 2007). 

The sweet potato is rich in vitamins B1 (thiamine), B2 (riboflavin), C (ascorbic acid) & E (tocopherol) as well as A. The minerals which are prevalent are calcium, potassium, magnesium and zinc. Dietary fiber and various non-fibrous carbohydrates are also common in the tuber. A number of African countries such as Mozambique (Low et al., 2007) and Uganda (Hotz et al., 2012) are growing the orange sweet potato to overcome the chronic vitamin A shortage in children.

The roots are rich in phenolic acids. The phenolic contents of the sweet potatoes cultivated in the USA range from 0.14 to 0.51 mg of chlorogenic acid equivalent/g fresh weight of hand-peeled storage roots. the main acids are chlorogenic and isochlorogenic acids (Walter et al., 1979). The phenolic content of of a red-fleshed sweet potato cultivar was found to be at an exceptionally high level of 9.45 mg/g fresh weight (32.2 mg/g dry weight)  (Cevallos-Casals & Cisneros-Zevallos, 2003). This compares with a fruit such as a blackcurrant which is measured at 21 mg CAE/g fw of berries (Amakura et al., 2000).

Japanese sweet potato is a staple feature of some important diets including the famous Okinawan diet. The yellow-fleshed version is the most common in Japan. There are a number of varieties grown in Japan including Chiran Murasaki, Tanegashima Murasaki, Naka Murasaki, and Purple Sweet. 

What Do They have Different Colours ?

Sweet potatoes have a rich and complex anthocyanin profile. Anthocyanins are the pigments which give most red-purple fruits their rich colour and this is no different in the sweet potato. Analysis shows two important types – cyanidin-3-(6′′-caffeoylsophoroside)-5-glucoside and peonidin-3-(6′′-caffeoylsophoroside)-5-glucoside (Montilla et al., 2010). Purple-fleshed sweet potatoes developed in Japan contain about 0.4–0.6 mg anthocyanins/g fresh weight (Furuta et al., 1998).

The purple varieties probably better health claims.

Cancer

There is an anthocyanin-enriched purple-fleshed sweet potato clone called P40 which has an anti-cancer effect in both cell cultures and in an animal model. In the study cited the suggestion was made that this P40 clone could protect against colorectal cancer because it stopped cell cycles in the cancer cells. The effect was attributed in part to the purple anthocyanins but also some phenolics.

Sweet Potato Leaves

The leaf is the byproduct of tuber production but has nutritional health properties in its own right. These have been consumed in traditional Chinese medicine to combat heart disease (arteriosclerosis), protect eyesight and reduce tumor production (Han, 2000). The juice from the plant is also consumed by people with diabetes mellitus (Type-2) in parts of India such as Sikkim and Darjeeling

References

Amakura, Y., Umino, U., Tsuji, S., & Tonogai, Y. (2000). Influence of jam processing on the radical scavenging activity and phenolic content in berries. Journal of Agricultural and Food Chemistry, 48, pp. 6292–6297.

Bovell-Benjamin AC (2007)  Sweet potato: a review of its past, present, and future role in human nutrition. Adv Food Nutr Res. 52 pp. 1-59. https://www.ncbi.nlm.nih.gov/pubmed/17425943

Cevallos-Casals, B. A., & Cisneros-Zevallos, L. A. (2003). Stoichiometric and kinetic studies of phenolic antioxidants from Andean purple corn and red-fleshed sweetpotato. Journal of Agricultural and Food Chemistry, 51, pp. 3313–3319

Chhetri, D.R.Parajuli, P. & Subba, G.C.(2005). Antidiabetic plants used by Sikkim and Darjeeling Himalayan tribesIndia Journal of Ethnopharmacology99, pp. 199202.

Furuta, S., Suda, I., Nishiba, Y., & Yamakawa, O. (1998). High tertbutylperoxyl radical scavenging activities of sweetpotato cultivars with purple flesh. Food Science and Technology International of Tokyo, 4, pp. 33–35.

Han, Z.M. (2000). Good Vegetable and Medicine–Ipomoea batatas leaf. Agriculture of Hunan Province6, pp. 27.

Harada, K., Kano, M., Takayanagi, T., Yamakawa, O., & Ishikawa, F. (2004). Absorption of acylated anthocyanins in rats and humans after ingesting an extract of Ipomoea batatas purple sweet potato tuber. Bioscience Biotechnology and Biochemistry, 68, pp. 1500–1507.

Hotz C, Loechl C, Lubowa A, Tumwine JK, et al. (2012) Introduction of beta-carotene-rich orange sweet potato in rural Uganda resulted in increased vitamin A intakes among children and women and improved vitamin A status among children. J. Nutr. 142 pp. 1871–1880. 

Lebot, V. (2009). Tropical root and tuber crops: cassava, sweet potato, yams and aroids (Vol. 17). Cabi.

Lim, S., Xu, J., Kim, J., Chen, T. Y., Su, X., Standard, J., … & Tomich, J. (2013). Role of anthocyanin‐enriched purple‐fleshed sweet potato p40 in colorectal cancer prevention. Molecular Nutrition & Food Research57(11), pp. 1908-1917.

Low, J.W., Arimond, M., Osman, N., Cunguara, B., et al. (2007) A food-based approach introducing white-fleshed purple skin sweet potatoes increased vitamin A intake and serum retinol concentrations in young children in rural Mozambique. J. Nutr. 137 pp. 1320–1327.

Montilla, E. C., Hillebrand, S., Butschbach, D., Baldermann, S., Watanabe, N., & Winterhalter, P. (2010). Preparative isolation of anthocyanins from Japanese purple sweet potato (Ipomoea batatas L.) varieties by high-speed countercurrent chromatography. Journal of Agricultural and Food Chemistry58(18), pp. 9899-9904. https://pubs.acs.org/doi/abs/10.1021/jf101898j

Oki, T., Masuda, M., Furuta, S., Nishiba, Y., Terahara, N., & Suda, I. (2002). Involvement of anthocyanins and other phenolic compounds in radical scavenging activity of purple-fleshed sweet potato cultivars. Journal of Food Science, 67, pp. 1752–1756.

Oki, T., Osame, M., Masuda, M., Kobayashi, M., Furuta, S., Nishiba, Y., et al. (2003). Simple and rapid spectrophotometric method for selecting purple-fleshed sweetpotato cultivars with a high radicalscavenging activity. Breeding Science, 53, pp. 101–107.

Steed, L. E., & Truong, V. D. (2008). Anthocyanin content, antioxidant activity, and selected physical properties of flowable purple‐fleshed sweetpotato purees. Journal of Food Science73(5), S215-S221.

Suda, I., Oki, T., Masuda, M., Kobayashi, M., Nishiba, Y., & Furuta, S. (2003). Physiological functionality of purple-fleshed sweet potatoes containing anthocyanins and their utilization in foods. Japan Agricultural Research Quarterly: JARQ37(3), pp. 167-173

Teow, C. C., Truong, V. D., McFeeters, R. F., Thompson, R. L., Pecota, K. V., & Yencho, G. C. (2007). Antioxidant activities, phenolic and β-carotene contents of sweet potato genotypes with varying flesh colours. Food Chemistry103(3), pp. 829-838.

Walter, W. M., Jr., Purcell, A. E., & McCollum, G. K. (1979). Use of high-pressure liquid chromatography for analysis of sweet potato phenolics. Journal of Agricultural and Food Chemistry, 27, pp. 942–946

Yoshinaga, M., Yamakawa, O., & Nakatani, M. (1999). Genotypic diversity of anthocyanins content and composition in purple-fleshed sweet potato. Breeding Science, 49, pp. 43–47.
Yoshimoto, M., Okuno, S., Yoshinaga, M., Yamakawa, O., Yamaguchi, M., & Yamada, J. (1999). Antimutagencity of sweetpotato (Ipomoea batatas) roots. Bioscience Biotechnology and Biochemistry, 63, pp. 537–541.

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