Geographical Variation in Nutritional Content of Baobab

The baobab (Adansonia digitata, Malvaceae) tree is indigenous to sub-Saharan Africa and is an important source of food and economic generation. Leaves, fruit, and seeds are eaten, and timber, fodder, and fibers from the tree are marketed. With roles in traditional medicine, culture, and religions, it is widely considered a sacred tree and often allowed to thrive in agricultural lands. Baobab is known to be high in vitamin C and other nutrients. However, nutritional studies on baobab vary greatly by sourced material and analytical methods. In addition, data on nutrients from east and south African baobabs have not been previously reported. Therefore, the authors analyzed fruit pulp and seeds from 17 populations in east, south, and west African nations (Kenya, Tanzania, Mali, Zambia, Zimbabwe, and Malawi) to determine if the region of origin affects nutrient content.

Provenances were from 8-1114 meters above sea level with rainfall of 463-1125 mm/year. Annual temperatures were 65.12-84.74°F (18.4-29.3°C). Ripe, unblemished fruits were taken from two to seven trees per provenance, randomly chosen for composite samples of two to five fruits each. Seeds were extracted, cleaned, and milled into flour. Pulp and seeds were tested for moisture, crude protein, ash, crude fat, crude fiber, carbohydrates, and for the following nutrients: calcium, potassium, magnesium, sodium, phosphorus, copper, iron, zinc, and manganese.* Tests were conducted in triplicate, and data subjected to analysis of variance (ANOVA), with trees nested by provenance and provenances by country.

While moisture in many common fruits ranges from 75% to 95%, baobab fruit was found to have approximately 9% moisture, similar to previously reported values. Statistically significant (P<0.001) differences in moisture were found among fruits from different nations. Pulp from Kenya and Mali were the moistest while those from Malawi and Zambia were the driest. Moisture was generally higher in fruits from east and West African nations. The authors say that the low moisture content may be due to low altitudes, low rainfall, and moderately high temperatures, but also that fruits with much greater moisture grow in the same places.

Mean protein ranged from 1.86% in Mali to 2.24% in Zambia. Previous studies found levels of 2.5-3.6%. A Tanzanian provenance (Kongwe) had the least protein in this study at 1.57%. This is much more than other common fruits. There were no clear regional trends in pulp protein content. Mean fiber ranged from 6.69% in Mali to 8.83% in Kenya, with three Kenyan provenances having the most fiber. However, fiber content from the Kenyan provenance did not differ statistically from that in other countries, showing that the influence of environment on fiber is minimal in baobab fruit. Studies of baobab fruits from Benin and the Guineo-Congolian zone also found high fiber. Pulp ash, indicative of mineral content, was highest in Kenya at 4.41% and lowest in Mali at 3.85%. Findings suggest that fruits from east and south Africa are richer in minerals than those from West Africa.

Seeds also showed differences. Most moisture contents were in Kenya (7.01%); lowest, Mali (5.67%). High temperatures may cause seed desiccation. Baobab seeds are high in essential amino acids, including lysine and tryptophan. Crude protein ranged from 15.18% in Malawi to 12.69% in Mali. East African seeds had much more protein than those from West Africa. However, protein levels in this study are much lower than reported for seeds from Benin. This suggests that West African soils may be poorer in nutrients needed for plant protein production. Seeds in this study had high levels of crude fiber (20.0-26.5%), values much lower than those earlier reported for Nigeria and Benin. Findings suggest that geographic conditions significantly influence seed fiber, but no clear regional trend emerged. Values for seed crude fat concurred with earlier reports, although higher fat content has been seen. Ash content of seeds (3.0-4.5%) was consistent with earlier reports. Baobab seeds, raw, roasted, or ground into flour, could provide important energy and protein in east Africa, where they are rarely eaten. In the Sahel region, they are used in sauces as thickeners and as flavor enhancers when fermented.

Mineral content of fruit pulp and seeds was also detailed. Again, there was variation among countries and provenances, some caused by altitude, rainfall, and/or soil content. This offers opportunities to select mother trees for domestication and development of cultivars rich in specific minerals. Potassium was the most abundant element in fruit and seeds, followed by phosphorus, magnesium, and calcium, but all minerals named were well-represented. Seeds had more phosphorus and magnesium than fruit.

Baobab fruit can be recommended as a source of dietary fiber. Flour from protein-rich seeds could improve cereal protein quality or be used to fortify other foods. Baobab fruit is an excellent source of calcium, endemic to dry regions of Africa where dairy products are scarce. Iron- and zinc-rich fruit from Kenya could supplement diets in mineral-poor east Africa. In West Africa, a condiment from fermented baobab seeds is part of daily diets. Fermentation decreases protein and carbohydrates but boosts fatty acids and free amino acids. This preparation could be useful in the east and South Africa. Stakeholders should promote the use of baobab flour, especially for children, pregnant women, and areas facing malnutrition. Studies of the baobab genome might give insight into interactions that determine plant mineral content. It would be valuable to restore this species where needed and introduce it to novel climates. Since baobab is associated with other species in agroforestry systems, species-species factors may also be considered.

*Although baobab is rich in vitamin C, this nutrient was not included in this study. Nor was an analysis made of baobab’s sugar (glycemic) content.

Resource:

Muthai KU, Karori MS, Muchugi A, et al. Nutritional variation in baobab (Adansonia digitata L.) fruit pulp and seeds based on Africa geographical regions. Food Sci Nutr. August 2017;5(6):1116-1129. doi: 10.1002/fsn3.502.

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