Medicinal plants are valuable and renewable sources of active substances in pharmacology. Approximately 20% of the plants in the world have been subjected to pharmacological and/biological evaluation and as such substantial number of new antibiotics are being introduced into the market obtained from natural or semi synthetic sources (Mothana and Lindequist, 2005; Aliyu et al., 2011). Many species in the genus Sacrocephalus have been reported to have extensive history in traditional me-dicine system, widely used for  the  treatment  of  malaria, of malaria hypertension, diarrhea, tuberculosis, dysentery and also as a laxative (Benoit-Vicalet.al., 1998). A number of researchers have reported the anti-bacterial (Fakae et-al., 2001) and antidiabetic properties of the plant. Phytochemical analysis revealed that the Sacrocephalus latifolius. contain alkaloids saponins, polyhenols and tannins (Tona et al., 2000; Boakye-Yiadom et al., 1977).

S. latifolius (Sm.) Bruce formerly known as Nauclea latifolia is a savanna shrub sometimes found in undisturbed fringing forest and closed savanna woodland. It belongs to the family Rubiaceae commonly called pin cushion tree, locally known as ‘Egbo egbesi in Yoruba, ‘Ubalu inu in Igbo and ‘Tabasiya’ in Hausa in Nigeria. It has many branches varying up to a height of 12 m with an open canopy. Flowers possess terminal spherical head like cymes of small whitish Flowers (Benoit-Vical et al., 1998). The flowers are found conjoined with their calyces. The fruit is syncarp and ripens during July to September. However, the baboons eat the fruits and disperse the seeds. It is further reported that livestock eat shoots and the leaves (Deeni and Hussain, 1991).

In West and Central Africa, S. latifolius is prominent  for its insecticidal and antiparasitic properties. In Gabon, Congo and Nigeria, infusions of the leaves and bark are used to cure fevers (Di Giorgio et al., 2006). In Kinshasa, DR Congo extracts and preparations, along with other plants, are administered for diagnosing diarrhea (Tona et al., 2000). S. latifolius is used in medicine and as food, thus serving the dual purpose of food and medicine (Etkin, 1996). This study evaluates the nutritional and medicinal properties of S. latifolius since it serves both as food and medicine.

Plant

Fresh leaves of S. latifolius were collected in bushes located around, Abuja, Nigeria. The plant was authenticated at the Herbarium unit of the Department of Biological Sciences, University of Abuja, Abuja, Nigeria. The leaves were air-dried at room temperature and grounded to fine powder, using a laboratory mill and stored in air-tight containers for laboratory analysis. All analysis was carried out in triplicates.

Proximate and mineral analysis

The proximate analysis of S. latifolius powdered leaf sample was tested to obtain values for the moisture content, crude fat, crude protein, crude fibre, ash and carbohydrates following the procedures as described by official methods of Analysis of Official Analytical chemists (AOAC, 1995). The moisture content was determined by air oven drying that exhibited a weight difference at 130°C for 1 h. The crude protein content by micro  Kjeldahl  method is given as 1% total nitrogen × 6.25 (AOAC, 1990). The crude fibre content was determined using dilute acid and alkali hydrolysis. Crude fat was extracted by exhaustively extracting 10 g of each sample in a soxhlet apparatus using dimethyl ether (boiling range 30 to 60°C) as the solvent. Ash was also determined by the incineration of 10 g of each sample placed in a muffle furnace maintained at 550°C for 5 h. The total carbohydrates content (on dry weight basis) was calculated by the difference: 100 - (crude protein + crude fat + ash + crude fiber).

The mineral constituents and vitamin analysis

The ash solutions  were prepared by weighing 5 g of each of the powdered samples and dried at 550°C in muffle furnace for about 5 h  and the resultant residues were  dissolved in 100 ml of deionized water. A standard  solution of the minerals (potassium, calcium, iron and zinc) to be analyzed were prepared. The atomic absorption spectrophotometer (model 200 – A, Buck Scientific) was set with power on for ten minutes to stabilize and the  standard mineral solutions were injected to calibrate the atomic absorption spectrophotometer (AAS)  using acetylene gas. Finally, an  aliquot of ash solutions were injected and the concentrations obtained from the AAS.

Vitamin analysis

Vitamin C in the sample was  determined as follows; 100 g of the fresh leaves of S. latifolius were cut into small pieces and grounded with a mortar and pestle. 10 cm³ of distilled water was added several times and decanted into a 100 ml. volumetric flask. The grounded leaves was strained through a cheese cloth, filtrate were collected and washed in volumetric flask. The extracted solution was made up to 100 ml with distilled water. 20 ml aliquots of the sample solution were pipette into a 250 ml conical flask, 150 ml distilled water and 1 ml starch solution was added. The sample was titrated with 0.005 m iodine solution. The end point of the titration was identified as the first permanent trace of a dark blue colour due to the starch iodine complex. The titrations were repeated two times with further aliquot of sample solution, with a constant result obtained  (Adeboye, 2008).

Phytochemical analysis

Extraction of plant material: In order to extract plant material, an equal amount of aqueous, chloroform and methanol were used as solvents for the extraction of bioactive compounds. The extracts so obtained were completely evaporated by using vacuum rotary evaporator. The resultant concentrated extracts were used for antibacterial activity.

Phytochemical screening: The phytochemical properties of the dried powdered plant leaf parts were determined using standard methods described by Harborne (1993) and Nabavi et al. (2008). The leaf extract was screened for glycoside, anthraqiunones alkaloids, tannins, terpenoids, flavonoids and saponins.

Test microorganisms: The test organisms used to detect the presence of antibacterial assay are Staphylococcus aureus and Escherichia coli. Cultures of these bacteria were maintained on the slopes of the nutrient agar at 37°C which were collected from Microbiology Laboratory of University  of Abuja  Teaching  Hospital, Gwagwalada, Abuja, FCT. Nigeria.

Antibacterial assay

The agar well diffusion technique  as described by Jombo and Enebebeaku (2007) was employed for the determination of the zone of inhibition of the extract. The minimum inhibiting concentration (MIC) was determined after  Baron and Finegold (1990) while the minimum bactericidal concentration was determined as  described by Jombo and Enebebeaku (2007). The same procedure was followed to know the frequency of occurrence of  standard antibiotics ampiclox for Staphylococcus aureus while chloramphenical was used for Escherichia coli to know the  zone of inhibition as controls.

Table 1 shows the result of the proximate analysis of S. latifolius. The concentration of organic compounds analyzed followed a sequential order of moisture > protein > ash > fibre > carbohydrate > fat. In Sacrocephalus species, the moisture content of the leaves (56.30%)  is higher than the reported value of Phyllanthus pentandrus (Aliero and Shehu, 2010). A high moisture content of  Sacrocephalus indicate that the plant  is susceptible to microbial attacks during storage. The low ash content of 5.93% reflects low mineral and high organic content  which are comparable to those recorded by Dike (2010). A very low content of fat  (0.28%) was found similar  when compared with the leaves of some higher plants by Dike (2010). However, the low fat content of the leaves of Sacrocephalus reveale d that  this plant is not an oil species and as such cannot be used either in industrial or domestic purposes, for industrial or domestic purposes. The fibre content of S. latifolius leaves was found to be 4.48% which validates the findings of Ujowundu et al. (2010) who reported the pre-sence of fibre content in the leaves of higher plants. It is revealed that the protein content (6.55%) was found to be lower than the values of Vernonia amygdalina (Dike, 2006)  carbohydrates content. However, the value of S. latifolius was 3.21% similar to those recorded for some leafy vegetables (Mensah et al., 2008).

The results showing presence of mineral composition are presented in Table 2. The presence of major elements like potassium, calcium, iron and zinc in the leaves correlates with the reports of Gafar et al. (2011). Potassium along with sodium is responsible for maintaining proper acid-base balance and nerve trans-missions in the body  (Akinyeye et al., 2010). Calcium plays an important role in building strong and healthy bones and teeth throughout life (Ojo and Ajayi, 2009). Iron helps in the formation of hemoglobin and myoglobin (Gafar et al., 2011). Zinc  speeds up the healing process after injury and  vitamin C content was relatively high when compared  to lettuce (USDA, 2005). However, the deficiency  in vitamin C leads to the disease scurvy  and the primary cause of vitamin C deficiency is a poor diet (king, 2008). Thus the vegetable leaves can be used as a supplement for vitamin C.

Table 3 shows the qualitative phytochemical analysis of leaves of S. latifolius. The results showed that the aqueous leaf extract of S. latifolius contains tannins, terpenoids, flavonoids and saponins. The chloroform leaf extract contains glycoside, tannin, terpenoids flavonoid and saponins. The methanolic leaf extract  contains glycoside, alkaloids, tannins terpenoids, falvonoids and saponins.

The antimicrobial activities of higher  plants are attributed to the presence of alkanoids and flavonoids (Cordell et al., 2001). The role of tannins and other compounds of phenolic nature as active antimicrobial compounds has been reported (Rojas et al., 1992). The presence of these phytochemicals  could  to some extent justify the observed antimicrobial activities exhibited by the extracts in the present study. The result of antibacterial assay of aqueous , chloroform and methanol extracts are presented in the Table  4. The extracts of S. latifolius  exhibited varying activities against S. aureus and E. coli as evidenced by its zone of inhibition when compared with the standard antibiotics of ampliclox for S. aureus and choramphenical of E. coli.

The highest zone of inhibition was observed at 200 mg/ml against S. aureus (18.0 mm) with methanol extract, while E. coli  exhibited  highest zone of inhibition at 21.0 mm with methanol extract. Aqueous extract has the least inhibition for both  organisms  at  all  concentrations.

Although, gram-negative bacteria tend to have higher intrinsic resistance to most antimicrobial agents (Ndukwe et al., 2005). However, there is impressive activity against this gram negative bacterium in gastrointestinal and urinary tract of the human body . The susceptibility of E. coil to the extracts is an indication to the therapeutic potentials of these extracts against such disease in Table  5. The growth of S. aureus was inhibited by the extracts with greatest inhibition in methanol. S. aureus is a human pathogen whose infection is difficult to treat with conventional antibiotics. In animals, S. aureus is encapsulated by fibrotic tissue and forms microabsceses to protect it from the usual antibiotics (Giesecke et al., 1994). Therefore, the activity of S. latifolius against S. aureus may prove to be a worthy alternative in search  of new antibiotics.

The phyotochemical screening of S. latifolius extracts shows  the presence of glycoside, alkanoids, tannins, terpenoid, flavonoids and saponins in Table 3. Differences in  antimicrobial  activity  of  medicinal  plants have been compared with the contents of active compound (Boakye-Tiadom and Konning, 1975). However, the  antimicrobial activities of higher plants are attributed to the presence of alkaloids and flavonoids (Cordell et al., 2001). The role of tannins and other compounds of phenolic nature as active antimicrobial compound has been reported (Rojas et al., 1992).  As such, presence of these phytochemicals could therefore justify the observed antimicrobial activities exhibited by the extracts of S. latifolius.

However, it was concluded from the present  study that S. latifoliu contain substantial amounts of organic substances and minerals,  representing the prospective nutrient composition. The result of phytochemical screening justified the antimicrobial activities and strongly confirm  its use in herbal medicine for the treatment of bacterial infection

The authors thank the Director General of National Institute of Pharmaceutical Research and Development (NIPRD), Abuja Nigeria for providing facilitie in conducting the research.

Authors have not declared any conflict of interest.