Wednesday, 10 January 2018
Food as Medicine: Okra (Abelmoschus esculentus, Malvaceae)
HerbalEGram: Volume 12, Issue 8, August 2015 Editor’s Note: Each month, HerbalEGram highlights a conventional food and briefly explores its history, traditional uses, nutritional profile, and modern medicinal research. We also feature a nutritious recipe for an easy-to-prepare dish with each article to encourage readers to experience the extensive benefits of these whole foods. With this series, we hope our readers will gain a new appreciation for the foods they see at the supermarket and frequently include in their diets. The basic materials for this series were compiled by dietetic interns from Texas State University in San Marcos and the University of Texas at Austin through the American Botanical Council’s (ABC’s) Dietetic Internship Program, led by ABC Education Coordinator Jenny Perez. We would like to acknowledge Perez, ABC Special Projects Director Gayle Engels, and ABC Chief Science Officer Stefan Gafner, PhD, for their contributions to this project. By Hannah Baumana and Allison Porterb a HerbalGram Assistant Editor b ABC Dietetics Intern (UT, 2014) History and Traditional Use Range and Habitat Okra (Abelmoschus esculentus) is a naturalized tropical and subtropical annual grown extensively in Asia and Africa. Growing up to 6 feet in height, okra plants have sturdy stems, long, broad, serrated, deeply-lobed leaves, and delicate yellow flowers marked with red or purple color toward the base.1,2 The edible portion of okra is the immature pod or fruit which contains the seeds.3 Inside the tapering, fuzzy pod is a soft tissue that exudes a mucilaginous (sticky) juice when cooked.4 The pods are commonly green, but other varieties have red or burgundy pods. Considered one of the most reliable annual edible vegetable crops of the tropics (the Latin term esculentus means edible), okra is tolerant of both hot, dry as well as hot, humid climates and is widely cultivated in West Africa, India, Southern Europe, and the Americas.5 Related to hibiscus (Hibiscus sabdariffa) and marshmallow (Althaea officinalis), okra was originally classified in the genus Hibiscus and was later reclassified into the genus Abelmoschus in the 18th century.3 Okra is believed to have originated in Ethiopia, where it still grows wild, although there is no definitive proof of its origin.3 Okra has been cultivated by the Egyptians since the 12th century BCE. From there it traveled to central Africa, the Mediterranean, and India.6 By the 17th century CE, okra had reached the New World via the slave trade in Africa and by the 19th century, it had spread to China.2 Phytochemicals and Constituents Okra is comprised primarily of water, carbohydrates, and protein with very little fat and a fair amount of dietary fiber.3 Okra is also a significant source of vitamin C and contains many other micronutrients such as calcium, phosphorus, iron, beta-carotene, and B vitamins. The carbohydrate content of okra is primarily in the form of mucilage, a long chain polysaccharide molecule made up of sugar units and amino acids. Thin-layer chromatography analytical methods indicate that the polysaccharides in okra gum contain galactose, galacturonic acid, rhamnose and glucose.7 This water-soluble mucilage is the source of okra’s viscous, slippery consistency, which is linked to okra’s effectiveness in treating gastritis and other conditions where the mucilage acts as a demulcent agent, i.e., it provides relief to inflamed mucous membranes. Phytochemical studies show that okra pods contain flavonoids, tannins, sterols, and triterpenes.5 Flavonoids are important compounds that are responsible for protecting tissues from oxidative damage in a variety of ways. Quercetin is the major antioxidant in okra gum, which is a key player in controlling inflammation in the body.7 Okra contains a moderate amount of oxalate, a compound that both is created by the human body and is present in plants. Because oxalate is excreted through urine and can calcify in the kidneys, high levels of oxalate intake along with genetic predisposition may lead to the development of kidney stones. Different types of kidney stones exist, but approximately 75% of patients diagnosed with kidney stones in the United States suffer from stones made of calcium oxalate.8 Physicians may recommend that patients with kidney stones or with a history of kidney stones follow a low-oxalate diet; however, a food’s oxalate content does not necessarily correlate with its oxalate bioavailability in the human body. Okra has been shown to have low oxalate bioavailability as compared to similar oxalate-rich foods such as peanuts (Arachis hypogaea) and almonds (Prunus dulcis).9 Oxalate absorption from dietary sources can be reduced when paired with foods with high calcium or magnesium content.10 Historical and Commercial Uses Ancient cultures quickly noted okra’s mucilaginous nature and its subsequent benefits to the digestive system. Okra was used by Egyptians to prevent the development of kidney stones.5 In folkloric practice, fresh, tender okra pods were consumed to cure constipation, leucorrhea (abnormal vaginal discharge), spermatorrhea (excessive, involuntary ejaculation), diabetes, and jaundice. The mucilage from okra is used commonly in traditional Asian and African medicine to treat gastritis, gastric ulcers, and to lubricate the intestines.5,11,12 The acceptance of okra as a relatively modern medicinal agent can be found in J.M. Nickell’s Botanical Ready Reference, a book published in 1911 in the United States for physicians and pharmacists.13 Arranged alphabetically by Latin binomial, okra appears as the first entry on the list of herbal drugs and medicinal agents. The actions noted for okra capsule (fruit) are “mucilaginous, demulcent, and edible.” Okra mucilage has been used traditionally in Arabic, West African, Caribbean, and Eastern Mediterranean cooking.6 The most common culinary application of okra is as a thickener for soups and stews. The most well-known application may be in Louisiana’s Creole gumbo stew, which may derive its name from a corruption of the Bantu word for okra: kingombo. It is also used as a substitute for egg whites and as a fat replacement in chocolate bars, cookies, and frozen dairy desserts.7 Okra can be boiled, baked, sautéed, stuffed, or fried. Sautéing or quickly frying the okra reduces the sticky texture significantly.4 The gummy texture can also be mitigated by cooking okra with cornmeal.14 The water extract of okra, also known as okra gum, is used as an industrial lubricant and as an emulsifier to stabilize foams and suspensions.9 It is also utilized medically in plasma replacement therapy.3 The seeds of the okra pods are roasted and powdered into a flour for use as a coffee substitute in Turkey, and in Nigeria, the nutritious flour is an important staple and often added to soups and other foods.4,15 In vitro studies done on the chemical composition and antioxidative properties of Nigerian okra seed flour demonstrated that antioxidant activity correlated positively with roasting time.15 This study showed that antioxidants within the okra seeds had the greatest benefit in protecting the human large intestine from oxidative damage. Modern Research Laboratory research suggests that okra and its extracts can be useful in the treatment of a variety of disease states. A recent in vitro study indicated that Abelmoschus esculentus lectin (AEL), a protein extracted from okra, binds carbohydrates on the surface of cancer cells, thus causing apoptosis (programmed cell death) and significantly and selectively inhibiting breast cancer cell proliferation.16 Modern research suggests that okra’s effectiveness in the treatment of gastrointestinal complaints can be attributed to the presence of rhamnogalacturonan polysaccharides, which disrupt the adhesion of Helicobacter pylori bacteria to stomach tissue;11 these bacteria are associated with stomach ulcers. The polysaccharide compounds bind non-specifically to different strains of H. pylori, inhibiting the binding of the pathogens to gastric cells. The rhamnogalacturonans appear to interact with H. pylori’s surface proteins, potentially providing a preventative treatment approach. Okra’s mucilage could also inhibit the recurrence of H. pylori infections by preventing re-colonization of the stomach following antibiotic eradication therapy. An in vitro study published in 2007 by the USDA Agricultural Research Service compared the effectiveness of the bile acid-binding, cholesterol-lowering drug cholestyramine to the natural bile acid-binding ability of the common vegetables okra, beets (Beta vulgaris), asparagus (Asparagus officinalis), eggplant (Solanum malongena), turnips (Brassica rapa subsp. rapifera), green beans (Phaseolus vulgaris), carrots (Daucus carota subsp. sativus), and cauliflower (B. oleracea var. botrytis).17 Okra was found to be more effective at binding bile acids than any other vegetable evaluated in the study, and 34% as effective as cholestyramine. An animal study conducted in 2011 found that okra peel and seed powder had the ability to normalize blood levels of both lipids and sugars in diabetic rats.18 Oral administration of okra significantly reduced blood levels of total cholesterol, triglycerides, low-density lipoproteins (LDL), very low-density lipoproteins (VLDL), and hemoglobin A1C as well as significantly increased blood levels of high-density lipoproteins (HDL) and hemoglobin. While both parts of the plant were effective in a dose-dependent manner, the seed powder had a more pronounced effect than the peel, especially on blood glucose levels. These results indicate that consumption of okra may help reduce hyperlipidemia and hyperglycemia in diabetics, thus helping to prevent cardiovascular disease and other comorbidities associated with diabetes. These effects could be related to okra’s ability to bind bile acids. Among other factors (e.g., soil, climate, season, etc.), cooking and preparation methods can impact the nutrient content of vegetables. A study on the effects of different cooking methods on the nutrient content of okra pods compared the mineral content of raw and cooked okra of both organic and conventional varieties.19 Raw okra had the highest concentration of all elements tested, indicating some degree of nutrient losses during cooking, with the most pronounced difference found in potassium concentration, while calcium losses were relatively minimal. There were significant mineral losses following boiling and baking, but the effect was less pronounced with sautéing.19 This could be due to the water solubility of nutrients found in okra, including but not limited to its mucilage. While the loss of mineral content may seem undesirable, the marked reduction of minerals from cooking could be beneficial for those with kidney disease. For example, potassium levels can be reduced by up to 60% by boiling okra and pouring off the water, making boiled okra safer than raw okra for a potassium-restricted diet. An in vitro study in 2011 examined the effects of okra gum extract on both cell viability and bacterial growth.7 Okra gum extract had antibacterial effects on seven of eight strains of bacteria tested, and was most effective against Staphylococcus aureus, Mycobacterium sp., M. aurum, Xanthobacter Py2, and Pseudomonas aeruginosa. In fact, okra gum extract was completely effective in inhibiting growth of S. aureus (which can cause skin infections, pneumonia, meningitis and septicemia) as well as P. aeruginosa (known for causing fatal lung infections in patients with cystic fibrosis). Major lipid fractions isolated from okra gum extract were 34% palmitic acid and 26% stearic acid, both of which have antibacterial properties against S. aureus and Listeria monocytogenes. The results of this study demonstrate the potential use of okra extract as an antibacterial agent with possible applications in the food and pharmaceutical industry. A study on rats explored the traditional uses of okra in liver disease.5 Hepatotoxicity was induced in rats that were then given an okra gum extract that quenched all free radicals present, thus preventing lipid peroxidation of liver cell membranes. The hepatoprotective and antioxidant activities of the okra extract are comparable to standard silymarin, isolated from milk thistle (Silybum marianum) fruit, making okra extract a potentially important substance for protecting chemically-damaged liver tissue. Human clinical trials are needed to explore this potential therapeutic application. Nutrient Profile20 Macronutrient Profile: (Per 1 cup [approx. 100 g] raw okra pods) 33 calories 2 g protein 7.5 g carbohydrate 0.2 g fat Secondary Metabolites: (Per 1 cup [approx. 100 g] raw okra pods) Excellent source of: Vitamin K: 31.3 mcg (39.1% DV) Vitamin C: 23 mg (38.3% DV) Very good source of: Folate: 60 mcg (15% DV) Vitamin A: 716 IU (14.32% DV) Magnesium: 57 mg (14.3% DV) Thiamin: 0.2 mg (13.3% DV) Dietary Fiber: 3.2 g (12.8% DV) Vitamin B6: 0.22 mg (11%DV) Good source of: Potassium: 299 mg (8.5% DV) Calcium: 82 mg (8.2% DV) Phosphorus: 61 mg (6.1% DV) Niacin: 1 mg (5% DV) Also provides: Zinc: 0.6 mg (4% DV) Iron: 0.6 mg (3.3% DV) Vitamin E: 0.27 mg (2.5% DV) DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet. Recipe: Spicy Okra Stew Adapted from New Flavors for Vegetables21 Ingredients: 3 large ripe tomatoes 1 lb fresh okra, stems removed, sliced 1/4-inch thick 2 tablespoons canola oil 1 yellow onion, diced Salt and freshly-ground black pepper, to taste 2 cloves of garlic, minced 1/2 teaspoon cayenne pepper 1/2 teaspoon ground coriander 1/2 teaspoon ground cumin 1/4-1/3 cup fresh parsley, chopped Directions: Prepare a small saucepan of boiling water and a separate bowl of ice water. Blanch the tomatoes: cut a shallow “x” at the bottom of each tomato, then cook in boiling water for 10 seconds. Immediately submerge in the ice water, let stand for 10 more seconds, then drain. Peel the skin from the tomatoes and chop the flesh. Heat the oil in a saucepan over medium heat. Add the onions and cook until just softened, 2-3 minutes. Add the okra and sauté until lightly browned, approximately 10 minutes, then lower the heat to medium-low and cook until tender. Add the garlic, salt, pepper, and spices, stirring until combined and fragrant, then add the tomatoes and 1 cup of water. Simmer until the tomatoes have broken down and the mixture begins to thicken. Adjust seasoning to taste, then remove from heat and stir in the chopped parsley. References Van Wyck B. Food Plants of the World. Portland, OR: Timber Press; 2006. Madison D. Edible: An Illustrated Guide to the World’s Food Plants. Washington, DC: National Geographic Society; 2008. Benchasri S. Okra (Abelmoschus esculentus (L.) Moench) as a valuable vegetable of the world. Ratarstvo i povrtarstvo. 2012:49:105-112. Onstad D. Whole Foods Companion: A Guide for Adventurous Cooks, Curious Shoppers, and Lovers of Natural Foods. White River Junction, VT: Chelsea Green Publishing; 2004. Alqasoumi SI. ‘Okra’ Hibiscus esculentus L.: A study of its hepatoprotective activity. Saudi Pharmaceutical Journal. 2012:20:135-141. Green A. 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