- Dioscorea is a genus of over 600 species of flowering plants in the family Dioscoreaceae, native throughout the tropical and warm temperate regions of the world.
- The genus was named by the monk Charles Plumier in honor of the ancient Greek physician and botanist Dioscorides.
- In the 1950s, scientists discovered the roots of wild yams contained diosgenin, a plant-based estrogen, which is hypothesized to aid in chemical defense against herbivores. It was used to create the first birth control pills during the 60s.
- Several species are known as yams, many of which are toxic when fresh, but eaten after detoxification. (22)
Nami is a twining vine, arising from tuberous roots,
and reaching a length of several meters. Stems covered with few or many
short, sharp spines. Leaves are 3-foliolate, the leaflets 12 to 20 centimeters long, somewhat
hairy, the lateral ones oblique, oblong-ovate, the terminal one equilateral, oblong to oblong-obovate. Panicle is axillary, slender, hairy, 12 to 20 centimeters long. Flowers are small; unisexual male flowers with 6 stamens; female
flowers similar to males, 3-winged, 3-celled, ovules 2 in each cell.
Fruit is a capsule, oblong and about 5 centimeters long. Flesh and sap of tubers are yellowish.
- Native to the Philippines.
Growing wild, chiefly in thickets
and forests at low and medium altitudes throughout the Philippines.
- Rarely cultivated.
- Also native to Andaman Is., Assam, Bangladesh, Bismarck Archipelago, Borneo, Cambodia, China, Hainan, Himalaya, India, Jawa, Lesser Sunda Is., Malaya, Maluku, Myanmar, Nepal, New Guinea, Queensland, Sulawesi, Sumatera, Taiwan, Thailand, Tibet, Vietnam. (13)
- Tubers yield alkaloid dioscorine a and 4-epidioscorine and a neuromuscular blocking agent.
- Study yielded a saponin glycoside, diosgenin.
The primary active ingredient in Dioscorea species, diosgenin is D. hispida is reported at 57µg/g dw.
- Study of mineral content reports the tubers are a good source of phosphorus, calcium and iron.
- A mature gadung tuber weighs up to 15 kg, each 100 g of tuber (wet basis) yields 20 g of carbohydrates, 78 g water, 1.81 g protein, 0.16 g fat, 0.93 g fiber and 0.69 ash.
- Extracts of tubers yielded hydroxybenzoic acid, hydroxycinnamic acid, and their derivatives. Peel yielded caffeic acid, chlorogenic acid, p-hydroxybenzaldehyde and methylester of protocatechuic acid. Phenolic acid content of both peel and flesh were very low. (11)
- Mineral analysis of tuber showed concentration of iron 0.6445 mg/100g, cadmium 0.0011 mg/100g, potassium 265.2780 mg/100g, calcium 5.1015 mg/100g, sodium 8.3011 mg/100g, magnesium 29.0237 mg/100g,
copper 0.1110 mg/100g, and zinc 0.6113 mg/100g. (27)
- Study of nutritional content yielded 22% moisture content
(low), 2.67% ash, 9.67% crude fat, 10% crude fiber, 2.99% protein, and 62.67% carbohydrates.
- Toxicity: The tuber is toxic when fresh due to the presence of saponins and calcium oxalate raphides.
Resistant starch is slowly digested in the lower parts of the GIT, with slow release and absorption of glucose. Starch is also gluten free.
- Sweet tart-tasting, cooling.
- Yellow flesh tubers reported to have a better taste than white flesh tubers.
Flesh and sap of the tubers are yellowish.
- Juice of underground stems reported to possess narcotic properties.
- Studies suggest anthelmintic, antioxidant, anti-inflammatory, analgesic, and anti-tumor activities.
- Tubers contain the poisonous alkaloid dioscorine, resembling
It is a nervous system paralyzant, not a protoplasmic poison.
- Neurotoxicity manifestations range from dizziness, altered consciousness, muscle paralysis and seizures.
It has been reportedly
used in criminal poisoning.
- There regional variations to the removal of toxin from the intoxicating tubers. Pulau Redang has several detoxification techniques. One requires thin slicing of yam, the soaking it in salted water for three days, then placing it in a sac to re-soak in a river or flowing water for another three days, finally testing edibility to see if fish would feed on them.
- In Papua New Guinea, the tubers are sliced and boiled for two days before cooking the yam.
- In Thailand, the Sakai remove the toxin by boiling with wood ashes.
- Study reports of reduction of cyanide concentration in tubers through immersion in sea water and interaction with rubbing ash. (see study below)
- Underground tubers, leaves.
Edibility / Nutrition
- Tuber crop is an important source of carbohydrates; has been used a staple foods during WWI.
- Roots used as food by the Ayta communities from Porac, Pampanga.
- Rootcrop, kurot or nami, used as supplementary food by the Hanunuo Mangyans of Mindoro. (20)
- The Alangan tribe of Mangyan in Mindoro, Philippines, use the tuber as an alternative to rice: the tuber is soaked for 3 days, then washed in running streams, dried for 2 days, then soaked for 2 hours before cooking it like rice.
- Despite known toxicity, in Thailand, where it is referred to as Kloi, tubers are used to make a dessert called Kao Nuew Kloi.
- In India used as famine food. Poison removed by boiling or keeping the tubers overnight in water.
- In Kerala, India, tuberous herb cooked with salt, chili, tamarind and tumeric powder and used as curry.
- Caution: See toxin removal.
- Tuber, raw or cooked used as anodyne and maturative for tumors and buboes.
- Also used
arthritic and rheumatic pains. sprains and contusions.
- Used by the Ayta communities of Porac, Pampanga for wounds and clotting. (16)
- Use poultice of freshly pounded material or decoction as external wash.
- In Bangladesh, tubers used to kill worms in wounds. Various plant parts used in whitlow, sores, boils, and bites of rabbit, jackal or dog.
- In India, tubers used for birth control. Also used for ulcer treatment.
- Tuber paste is applied to peeling skin of feet.
- In Malaysia, pounded leaves applied to sores of yaw.
- In Johore, decoction of tuber used as alterative and diuretic in chronic rheumatism.
- In Malaysia, the Temuan tribe uses pounded leaves from intoxicating yam for healing sores of yaw.
Infusion of corms of detoxicated tubers used to decrease blood glucose. Tendril of yam have been used as deworming medicine.
- In Thailand, used to treat constipation.
• Bleaching: Yellow juice from the flesh and sap of tubers is used for bleaching
clothes and abaca fibers.
• Poison: Juice of tubers used in criminal poisoning.
Also, used as an ingredient together with Antiaris toxicaria in the preparation of arrow poisons.
• Intoxicant: Jeypore people of India reportedly use the intoxicating effect of D. hispida to forget their sorrows, as they get an effect similar to drinking beer.
• Insecticidal: Residue after extraction of poison used as insecticidal.
• Livestock: Tubers used as cure for myiasis of the scrotum in carabaos.
• Phytochemicals / Phenolic Content:
Study showed phenolic acids were present in only small amounts in Kloi tuber, compared to relatively high phenolic content for other yam Dioscorea species. The anomaly was attributed to the sample preparation, hydrolysis time and/or pH. Preliminary findings and documented nutritive value suggest the tuber as a potential source of phytochemicals for cosmetic, pharmaceutical or dietary antioxidant use. (2)
• Anti-Inflammatory / Analgesic:
Study of extract of D. hispida in animal models showed potent analgesic and anti-inflammatory effects and therapeutic efficacy, comparable to standard drugs Pentazocine and indomethacin respectively. (3)
• Toxicity Study: Study
of ethanolic extract showed no toxicity or death at given test dose levels. LD50 was >2000 mg/kbw for the extract.
• Hypoglycemic Effect: Study in alloxan-induced hyperglycemic rats evaluated the hypoglycemic effect of a water soluble polysaccharide extracted from yam tuber (D. hispida). All the WSP extracts exhibited an ability to decrease blood glucose in hyperglycemic condition as well as inhibit glucose absorption and short chain fatty acid (SCFA) formation. (4)
• Gadung Starch / Modification with Raw and Ginger Oil: Use of starch is limited by its high content of toxic substances, i.e. alkaloids and hydrogen cyanide in free and bound forms, high moisture content and a disposition to post harvest deterioration. Previous efforts have been successful in reducing the bitter and toxic compounds to a safe level. Study showed processing and modification resulted properties comparable to American wheat flour. One drawback was the presence of remaining ginger aroma. (7)
• Pharmacologic Effects of Extracts: Purified extracts studied in animals showed: (1) Properties resembling nicotine (2) Injection caused hyperpnea, tachycardia, increase in blood pressure, contraction of nictitating membrane. (3) Rise in BP and contraction of nictitating membrane and of smooth muscle were inhibited by pretreatment with hexamethonium. (4) Striated muscle contraction was inhibited by pretreatment with d-turbocurarine.
• Antitumor / Ehrlich Ascites Carcinoma / Antioxidant: Study evaluated D. hispida against an animal model of Ehrlich Ascites Carcinoma. An ethanolic extract showed significant anticancer activity at varying doses, increasing survival, and decreasing tumor burden. Reduced elevated levels of lipid peroxidation was attributed to a high content of phenolic compounds. (10)
• Mosquito Repellent Additive: Study showed nami (Discorea hispida) tuber crude extract added to the citronella, neem, and eucalyptus mosquito repellent product is very acceptable based on skin tolerance and overall repellency, while providing a non-irritating alternative to synthetic compounds. (12)
• Dioscorine / Neurotoxic / Dried Tubers: Dioscorea hispida contains the neurotoxic dioscorine, an isoquinuclidine alkaloid that causes nervous system paralysis. Study evaluated the dioscorine content of D. hispida dried tubers in Thailand. TLC-densitometry and TLC image analysis yielded a dioscorine content of 0.72 ± 0.07 % w/w and 0.66 ± 0.07 % w/w, respectively. (14)
• Starch-Based Hydrogels / Disinfectants: Novel Dioscorea hispida starch-based hydrogels
inhibited Escherichia coli, Staphylococcus aureus, Saccharomyces cerevisiae, and Salmonella typhimurium growth. it showed an acceptable level of toxicity. Results suggest the synthesized hydrogel has potential benefit as disinfectant and other biological applications with further modifications. (15)
• Hypnotic Effect / Leaves: A previous study has shown the aqueous crude extract of nami leaf to have sedative effect. This study evaluated and compared an aqueous leaf extract with 70% v/v methanol leaf extract in BALB/c mice. Results showed the crude aqueous leaf extract to possess potent hypnotic activities, supporting its therapeutic effect for insomnia. However, on semi-purification, no significant hypnotic effect was observed. (17)
• 1937 Toxicological
Study: This 1937 study reports on the toxicological evaluation of Dioscorea hispida. It makes mention of nami as a cause of accidental food poisoning and use with criminal intent. An alkaloid was present, more or less uniformly distributed, in both cortical and medullary parts. The toxicity was tested on mosquito fish, mice, and monkey; by analogy, the fatal dose for a 50 kg ma would be 2.5-3 gm. (18)
• Anthelmintic / Leaves: Study investigated alcoholic extracts of leaves of D. hispida for anthelmintic activity against Pheretima posthuma. Results showed significant anthelmintic activity comparable to standard Albendazole. (19)
• Potential as Rodenticide: Study evaluated a formulation of yam-tuber as rodenticide for rat pest control using three treatment doses i.e., 300 g, 600 g, and 900 g of yam tuber. Rats that fed on baits showed slow motion movement, quiet stay, shaking, paralysis before death and the higher the dose the more significant the effects. (21)
• Thrombolytic / Membrane Stabilizing / Antioxidant / Antimicrobial: Study evaluated a methanol extract of plants and soluble fractions for various biologic activities. A carbon tetrachloride soluble fraction (CTCSF) showed substantial phenolic content, strong free radical scavenging and moderate antimicrobial effects. The PETSF and CTCSF significantly (p<0.05) inhibited heat- and hypotonic solution-induced erythrocyte membrane lysis. The aqueous soluble fraction (AQSF) demonstrated significant (p<0.05) thrombolytic activity. (23)
• Oxidative Stress and DNA Damage Effect on Placental Tissue: Study evaluated the effect of D. hispida on the production of reactive oxygen species (ROS) and their effects on DNA damage in Sprague Dawley rat's placental tissues. There was not significant production of ROS and SOD activities. Comet assay revealed a significant increase (p<0.05) of DNA damage on animals treated with 250 and 500 mg/kg BW DHAE. It was postulated the placental cells could have undergone necrosis, which destroys all components including DNA. The high amount of hydrogen cyanide and other compounds in 1000 mg/kg BW DHAE could elevated lipid peroxidation and directly induce cell necrosis. (24)
• Reducing Cyanide Levels in Bulbs: Study evaluated the reduction of high concentration of cyanide in D. hispida through immersion in seawater and interaction with rubbing ash. Results showed immersion time for 12, 24, and 36 hours could reduce cyanide concentrations about 48.30%, 64.44%, and 70.88%, respectively. Interaction by using 75% rubbing ash for 12, 24, and 36 hours can reduce cyanide concentration in tubers by 24.09%, 38.69%, and 51.42%, respectively; and with 100% rubbing ash, 36.26%, 49.92%, and 59.63%, respectively. Further treatment with drying and fermentation lowers cyanide concentration about 88.68% with a soft and white texture. (25)
• Antibacterial / Antibiofilm: Cyanide Levels in Bulbs: Study evaluated the effectiveness of D. hispida as an antibacterial and antibiofilm agent against selected pathogenic and non-pathogenic bacteria. Extracts were tested against growth of planktonic bacterial cells. All bacteria treated with D. hispida showed significant (p<0.05) reduction in planktonic cell and biofilm densities. Results suggest D. hispida demonstrated antimicrobial and antibiofilm capabilities, and can complement current antimicrobials to maximize killing efficiency and minimize occurrences of resistance. (26)
• Novel Natural Coagulant in Textile Wastewater Treatment: Study evaluated Dioscorea hispida starch as a natural coagulant in coagulation-flocculation for purification of textile effluent from dyeing and finishing mills. Dioscorea hispida starch yielded was 15.38% dry weight. Optimum dosage of D. hispida starch of 2500 mg/L resulted in maximum reduction of 22%, 93%, 63% of COD, turbidity, and color, respectively. Results suggest potential for utlization as natural coagulant with relatively good removal efficiency in textile wastewater treatment. (28)