Tylosema esculentum

Tylosema esculentum, the Morama bean, is a long-lived perennial legume native to arid areas of southern Africa. Stems grow at least 3 metres, in a prostrate or trailing form, with forked tendrils that facilitate climbing. A raceme up to 25mm (1 inch) long, containing many yellow-orange flowers, ultimately produces an ovate to circular pod, with large brownish-black seeds.

Name

Also known as Morama; Camel's foot; Gemsbuck beans; tamani berry; morama bean; braaiboontjie (Afrikaans)

Form

Summer growth is typically prodigious, particularly in plants older than one year - due in part to its large underground tuber. The plant is dormant over winter in its native home - South Africa, Namibia and Botswana - but might possibly remain evergreen in less harsh environments.
The morama bean is adapted to its native region of Southern Africa and therefore grows in dry and low-moisture soils. Its drought tolerance is accordingly high. The fact that the morama bean is used to harsh environments offers potential to extend the agricultural activity into regions which are dry or unproductive at the moment. Nevertheless it needs to be investigated whether it can grow on different soil types.^[1]

The nutritional value of the morama bean is astonishingly high for an unimproved legume. The tubers have a high protein content of 9.0% and also have a high amino acid content. The tubers of cassava, for example, only have a protein content of 1-3%, while yam has one of 7%. Also the grain is relatively high in protein with a share of 30-39%. The concentration of sulphur-containing amino acids is high as well (with a lysine content of 5.0% and a methionine content of 0.7%). This shows that the protein content of the seeds is comparable to the one of commercial soybeans, which have a content of 38-40%. Therefore the potential of the morama bean is high to replace the soybean as a protein source, once there have been genetical improvements. ^[2]

The tuber can grow very large - at least 10 kg, perhaps much larger. In Botswana a tuber of 277 kg has been found.

The seeds develop in typical legume pods, albeit large and squat in shape - with typically one or two seeds per pod.

Uses

The plant is a significant food-source for the people of the Kalahari because of the high protein and oil content of its large seeds (20-30gm each). The seeds are usually roasted, imbuing them with a more palatable flavour - comparable to cashew or chestnut. The seeds can also be ground or boiled. The beans keep well, due to their hard outer shell.

The tuber is also edible, but needs to be harvested from young plants (one or two years old) - after this age the tuber becomes astringent and fibrous.

Another interesting marama bean product is its flour. The flour of Tylosema esculentum, prepared from heated or unheated marama beans, has a potential as a functional food ingredient. However studies about its nutritional and physicochemical properties are lacking, the flour is protein-rich. Protein-based ingredients of marama bean are similar to those commercially available from soybean. Therefore, the flour of Tylosema esculentum has the potential to be used as a protein supplements in composite flours with cereals to improve the protein quality.^[3]

Morama milk

The milk of the morama bean is a creamy white water extract very similar to dairy milk or soymilk. The milk can be consumed in the form of a refreshing and nutritious beverage just like dairy milk or soymilk. Though it is not available commercially.^[4]

The milk of the morama bean has high levels of sodium (47.9 mg/100 g) and iron (3.7 mg/100 g) compared to soymilk and dairy milk. But is shows much lower calcium contents (6.8 mg/100 g).^[5]

In order to get morama milk several processing steps are involved: Thermal treatment (blanching and roasting of the beans), cracking, milling, suspending in water, boiling and filtration to obtain a milk-like phase.^[4]

Forage

The potential uses of the morama bean go beyond the role of only being a food plant. The foliage of the plant serves as forage for livestock and wildlife in Southern Africa because the leaves are highly palatable. Since the morama bean is used to grow in harsh environments it could be used as a feed crop in the drier parts of Africa. While using it as forage one does also protect the soil by conserving its moisture and preventing from soil erosion by wind and water. Furthermore there would be a build-up in organic matter, which would be beneficial for soils which are poor in nutrients.^[6]

Propagation

The seed's hard outer shell means that scarification is necessary in order to ensure satisfactory germination rates.^[7] As for most legumes, a pH neutral soil is preferred. The plant typically grows in very sandy loam, where waterlogging would not be a problem. Despite much global interest in this plant, propagation rates are still fairly low.

The plant can be grown outside, unsheltered, as far north as Zone 8 in the United States and perhaps further north; above ground growth is killed back by winter freezing, but the plant reemerges each Spring in late May. The greatest impediment to producing a crop of seeds is the long maturation time for the seed pods - which is right up to the first hard freeze of the year. Waterlogging is indeed an issue - leading to root rot - and a well drained sandy loam is preferred, but not essential.

Curiously, this and the other three members of the genus Tylosema are possibly unique within the family Fabaceae in the fact they exhibit heterostyly.^[8] This reduces propagation potential, and obviously reduces seed production rates for cropping.

Pests

There is yet not much reported about diseases. But two fungi are coinfecting the pods of morama beans leading to necrotic leasons. The fungi were revealed to be Alternaria tenuissima and Phoma spp. Also, insect pests could have been observed causing seed damage. But the identity of these insects are not confirmed yet.^[4]

Chemical and nutritional composition

It is most common to eat the morama beans as mature beans when the seeds are surrounded by a hard and woody seed coat, which has a reddish to brownish color. But the beans can also be eaten when they are still immature green beans.^[4]

Moisture

The morama bean has a very low moisture content as the dry matter content ranges from 93.4 % to 98.7 %. The moisture content may also vary due to external factors.^[9][10][11]

Lipids

It was reported that the content of lipids ranges between 24 % and 42 %. This high amount of lipids is an advantage, especially in Southern Africa where it helps improving the status of the undernourished people. ^[4] The lipid content of the morama beans can be compared to sunflower seeds (22-36 %) and rapeseed (22-49 %) and almost reaching the amount that is found in peanuts (45-55 %).^[12][13] The amount of lipids is twice as high as found in soybeans (17-20 %).^[12][14]

Protein

The protein range of morama beans ranges from 29% to 39% on a dry matter basis. Thus, it it comparable or slightly higher to most other legumes. This amount of protein makes the morama bean a great nutritive food but can be also used as a protein-rich ingredient for supplementing other products.^[4]

References

External links

• Annals of Botany report on "Functional Heterostyly in Tylosema esculentum"
• Food and Agricultural Organisation of the United Nations
• Morama Engaged: Increasing community awareness and utilization of indigenous grains to improve nutrition security and livelihoods in Botswana and Namibia