Nutrition Raw yam has only moderate
nutrient density, with
appreciable content (10% or more of the
Daily Value, DV) limited to
potassium,
vitamin B6,
manganese,
thiamin,
dietary fiber, and
vitamin C (table). But raw yam has the highest potassium levels amongst the 10 major staple foods of the world (
see nutritional chart). Yam supplies of
food energy per 100 grams. Yam generally has a lower
glycemic index, about 54% of
glucose per 150-gram serving, compared to potato products. The protein content and quality of roots and tubers is lower than other food staples, with the content of yam and potato being around 2% on a fresh-weight basis. Yams, with
cassava, provide a much greater proportion of the protein intake in Africa, ranging from 5.9% in East and South Africa to about 15.9% in humid West Africa. As a relatively low-protein food, yam is not a good source of
essential amino acids. Experts emphasize the need to supplement a yam-dominant diet with more protein-rich foods to support healthy growth in children. Yam is an important dietary element for Nigerian and West African people. It contributes more than 200 calories per person per day for more than 150 million people in West Africa, and is an important source of income. Yam is an attractive crop in poor farms with limited resources. It is rich in starch, and can be prepared in many ways. It is available all year round, unlike other, unreliable, seasonal crops. These characteristics make yam a preferred food and a culturally important food security crop in some sub-Saharan African countries.
Comparison to other staple foods The following table shows the nutrient content of yam and major staple foods in a raw harvested form on a
dry weight basis to account for their different water contents. Raw forms, however, are not edible and cannot be digested. These must be sprouted, or prepared and cooked for human consumption. In sprouted or cooked form, the relative nutritional and antinutritional contents of each of these staples is remarkably different from that of raw form of these staples.
Storage Roots and tubers such as yam are living organisms. When stored, they continue to respire, which results in the oxidation of the
starch (a polymer of glucose) contained in the cells of the tuber, which converts it into water,
carbon dioxide, and heat energy. During this transformation of the starch, the dry matter of the tuber is reduced. Amongst the major roots and tubers, properly stored yam is considered to be the least perishable. Successful storage of yams requires: • initial selection of sound and healthy yams • proper curing, if possible combined with fungicide treatment • adequate ventilation to remove the heat generated by respiration of the tubers • regular inspection during storage and removal of rotting tubers and any sprouts that develop • protection from direct sunlight and rain Storing yam at low temperature reduces the respiration rates. However, temperatures below cause damage through chilling, causing a breakdown of internal tissues, increasing water loss and yam's susceptibility to decay. The symptoms of chilling injury are not always obvious when the tubers are still in cold storage. The injury becomes noticeable as soon as the tubers are restored to ambient temperatures. The best temperature to store yams is between , with high-technology-controlled humidity and climatic conditions, after a process of curing. Most countries that grow yams as a staple food are too poor to afford high-technology storage systems. Sprouting rapidly increases a tuber's respiration rates, and accelerates the rate at which its food value decreases.
Consumption Yams are consumed in a variety of preparations, such as flour or whole vegetable pieces across their range of distribution in Asia, Africa, North America,
Central America, the
Caribbean, South America, and
Oceania. Among the Akan of Ghana, boiled yam can be mashed with palm oil into
eto in a similar manner to the plantain dish
matoke, and is served with eggs. The boiled yam can also be pounded with a traditional mortar and pestle to create a thick, starchy paste known as
iyan (pounded yam) which is eaten with traditional sauces such as
egusi and
palm nut soup. Another method of consumption is to leave the raw yam pieces to
dry in the sun. When dry, the pieces turn a dark brown color. These are then milled to create a brown powder known in Nigeria as
elubo. The powder can be mixed with boiling water to create a thick starchy paste, a kind of pudding known as
amala, which is then eaten with local soups and sauces. Yams are a staple agricultural
commodity in
West Africa with cultural significance,
Brazil Yams are particularly consumed in the coastal area of the
Northeast region, although they can be found in other parts of the country. In
Pernambuco state, it is usually boiled and served cut in slices at breakfast, along with
cheese spread or
molasses.
Colombia In Colombia yam production has been specifically located in the
Caribbean region, where it has become a key product in the diet of the population of this area. In 2010, Colombia was among the 12 countries with the highest yam production worldwide, and ranked first in yield of tons per hectare planted. Although its main use is for food, several studies have shown its usefulness in the pharmaceutical industry and the manufacture of bioplastics. However, in Colombia, there is no evidence of the use of this product, other than food.
Philippines market (
Vanuatu) ) In the Philippines, the purple
ube species of yam (
D. alata), is eaten as a sweetened dessert called
ube halaya, and is also used as an ingredient in another Filipino dessert,
halo-halo. It is also used as a popular ingredient for ice cream.
Vietnam In Vietnam, yams are used to prepare dishes such as
canh khoai mỡ or
canh khoai từ. This involves mashing the yam and cooking it until very well done. The yam root was traditionally used by peasants in Vietnam to dye cotton clothes throughout the Red River and Mekong delta regions as late as the mid-20th century, and is still used by others in the
Sapa region of northern Vietnam.
Indonesia In Indonesia, the same purple yam is used for preparing desserts. This involves mashing the yam and mixing it with coconut milk and sugar. White- and off-white-fleshed yams are cut in cubes, cooked, lightly fermented, and eaten as afternoon snacks.
Japan , Japanese dish prepared from tororo (D. polystachya) and maguro'' (tuna) An exception to the cooking rule is the mountain yam (
Dioscorea polystachya), known as
nagaimo and can be further classified into
ichōimo (lit. 'ginkgo-leaf yam'; kanji: 銀杏芋), or
yamatoimo (lit. Yamato yam; kanji:
大和芋), depending on the root shape. Mountain yam is eaten raw and grated, after only a relatively minimal preparation: the whole tubers are briefly soaked in a vinegar-water solution to neutralize irritant
oxalate crystals found in their skin. Another variety of yam,
jinenjo, is used in Japan as an ingredient in soba noodles. In Okinawa, purple yams (
Dioscorea alata) are grown. This purple yam is popular as lightly deep-fried tempura, as well as being grilled or boiled. Additionally, the purple yam is a common ingredient of yam ice cream and cake with the signature purple color.
India In central parts of India, the yam is prepared by being finely sliced, seasoned with spices, and deep fried. In Southern India, the vegetable is a popular accompaniment to rice dishes and curry. The purple yam,
D. alata, is also eaten in India, where it is also called the violet yam. Species may be called by the regional name "taradi", which can refer to
D. belophylla,
Dioscorea deltoidea, and
D. bulbifera. Digging and selling taradi is a major source of income in the region of
Palampur.
Nepal Dioscorea root is traditionally eaten on
Māgh Sankrānti (a midwinter festival) in Nepal.
Fiji Islands Yam is, along with
cassava and
taro, a staple food, and is consumed boiled, roasted in a
lovo, or steamed with fish or meat in
curry sauce or
coconut milk and served with rice. The cost of yam is higher due to the difficulty in farming and relatively low volume of production.
Jamaica Because of their abundance and importance to survival, yams were highly regarded in
Jamaican ceremonies and constitute part of many traditional
West African ceremonies.
The West Yam powder is available in
the West from grocers specializing in African products, and may be used in a similar manner to
instant mashed potato powder, although preparation is a little more difficult because of the tendency of the yam powder to form lumps. The powder is sprinkled onto a pan containing a small amount of boiling water and stirred vigorously. The resulting mixture is served with a heated sauce, such as
tomato and
chili, poured onto it. Skinned and cut frozen yams may also be available from specialty grocers.
Phytochemicals and use in medicine The tubers of certain wild yams, including a variant of '
Kokoro' yam and other species of
Dioscorea, such as
Dioscorea nipponica, are a source for the extraction of
diosgenin, a sapogenin steroid. Such preparations were used in early
combined oral contraceptive pills. The unmodified steroid has
estrogenic activity. == In culture ==