The baobab tree (Adansonia digitata, Malvaceae) grows in semi-arid regions of Africa. The tree is a source of food, water, medicine, fiber, and building materials for indigenous people. Baobab fruit dries while it is still on the tree, and the dried fruit pulp is used to prepare a variety of foods. The fruit and leaves are used in African traditional medicines such as antipyretics, immunostimulants, anti-inflammatories, analgesics, and probiotics. The fruit pulp is reported to have antioxidant, hepatoprotective, cardioprotective, and antidiabetic effects. A few studies have analyzed the secondary metabolites present in baobab fruit, but those studies suggest highly variable profiles depending on where the fruit was grown. The purpose of this study was to determine the chemical profile, with emphasis on secondary metabolites, and to evaluate antioxidant and antidiabetic effects of baobab fruit and leaves grown in Mali.
Samples of baobab dried fruit pulp were purchased from local markets in three regions of Mali and labeled as Fruit One, Fruit Two, or Fruit Three. Fruit One was from Baraoueli, Fruit Two was from Bandiagara, and Fruit Three was from Segou. Leaves from baobab trees grown in the Segou region were obtained from the Women’s Herbalist Association in Bamako, Mali. The dry fruit and leaf samples were extracted first with hexane and then with methanol. Chlorophyll was removed using solid-phase extraction. The methanol extracts were further extracted or purified to prepare samples for analysis.
Total phenolic content and antioxidant activity of fruit pulp
Fruit pulp samples were analyzed for total phenolic content (TPC) using the Folin-Ciocalteu assay, and results were expressed as mg gallic acid equivalents (GAE) per gram dried extract. TPC ranged from 120.07 mg to 161.40 mg GAE per gram. Five methods were used to assess antioxidant activity. Fruit Three extract had the greatest reducing power and radical scavenging activity toward synthetic radicals, the greatest ferric ion reducing power, and the greatest inhibition of β-carotene oxidation. Fruit One extract had the greatest antioxidant activity against the superoxide radical, and all three fruit extracts had greater activity than vitamin C in this assay.
Inhibition of α-glucosidase by fruit pulp
α-Glucosidase is an enzyme that breaks down starch into glucose in the small intestine. The fruit pulp extracts were tested for α-glucosidase inhibition, using acarbose as the standard. Acarbose is an antidiabetic drug that slows the digestion of carbohydrates by inhibiting α-glucosidase. The fruit extracts inhibited the enzyme in a dose-dependent manner and at much lower concentrations than acarbose. The IC50, the concentration at which 50% of α-glucosidase was inhibited, ranged from 1.71 μg to 2.39 μg per mL for the fruit extracts and 358.75 μg/mL for acarbose.
Chemical composition of fruit pulp
Composition of the fruit pulp extracts was analyzed using combined high-performance liquid chromatography (HPLC) and mass spectrophotometry (MS) techniques. Citric acid and 14 phenolic compounds were identified. The phenolic compounds with the highest concentrations were, in decreasing order, tiliroside, catechin plus epicatechin, procyanidins, feruloyl quinic acid, kaempferol 3-O-glucoside, kaempferol, and quercetin 3-O-glucoside. Baobab fruit from Cameroon is reported to contain dicaffeoylquinic acid and apigenin glycosides, which were not detected in the fruit from Mali. Baobab fruit from Nigeria is reported to contain iridoid, phenylethanoid, and hydrocinnamic acid glycosides, which were not detected in the fruit from Mali or reported in the fruit from Cameroon.
Chemical composition of leaves
Composition of baobab leaves was analyzed using combined HPLC and MS techniques, and 18 phenolic compounds were identified. Compounds found in leaves but not fruit extracts included rutin, quercetin, apigenin O-pentoside, and vitexin/isovitexin. Concentrations of phenolic compounds in the leaves were not reported. The profile of baobab leaves from Mali is similar to the profile of leaves from Cameroon, while leaves from Nigeria are reported to have a different profile and fewer phenolic compounds.
The authors conclude that Malian baobab fruit pulp and leaves are rich sources of polyphenols that have antioxidant, antidiabetic, and other health-promoting effects. The phytochemical profile of baobab fruit grown in Mali differs from profiles of baobab fruit grown in other African countries. The authors recommend further studies to characterize baobab fruit and leaves from different countries and to better understand how the growing region influences the phytochemical composition. The authors state that baobab fruit is the most important foodstuff of the flora of Mali. It provides energy and nutrients in a country where malnutrition is prevalent. Baobab represents a promising local source of new food products, food supplements, and plant-based medicines.
Braca A, Sinisgalli C, De Leo M, et al. Phytochemical profile, antioxidant and antidiabetic activities of Adansonia digitata L. (baobab) from Mali, as a source of health-promoting compounds. Molecules. November 2018;23(12):3104. doi: 10.3390/molecules23123104.