Abstract

Background: Ocimum gratissimum and Solanum aethiopicum are widely utilized medicinal plants employed in ethnomedicine for the treatment of myriads of health abnormalities including anaemia, constipation, inflammation and ulcers. The present study compared the nutritional compositions of these two medicinal plants. Methods: The leaf of these plants were destalked and air-dried differently for 8 days. The dried samples were milled into fine powder using an auto-milling machine. The homogenized samples were subjected to quantitative analysis and atomic absorption spectrophotometry for phytochemical and mineral determinations respectively, while proximate analysis was determined by the methods described by Association of Official Analytical Chemists (AOAC). Results: There were significant (p<0.05) increase in the percentage compositions of alkaloid, saponin and phytate in Solanum aethiopicum when compared to Ocimum gratissimum. On the other hand; tannin, flavonoid and phenols significantly increased (p<0.05) in Ocimum gratissimum more than Solanum aethiopicum. All the quantified proximate and mineral compositions (Ca²⁺, Mg²⁺, K⁺, Na⁺, P, Fe²⁺, Zn²⁺) were significantly higher (p<0.05) in O. gratissimum compared to S. aethiopicum. Again, S. aethiopicum revealed higher moisture content (84.33 %) than O. gratissimum (8.99 %). Conclusion: The results revealed higher nutritional composition in Ocimum gratissimum than Solanum aethiopicum. Therefore, increase consumption of these nutritional and medicinal compliant plants will help in diet formulation and alleviate the scourges associated with malnutrition in the population.

1. Introduction

In recent years, the desire to adopt a healthy dietary lifestyle has rekindled the interest of scientists all over the world into investigation of nutritional potentials of vegetables. Again, the importance of vegetables as valuable sources of nutrients has been reported ^{1, 2}, while some of them have medicinal properties ³. Vegetables contribute significantly to food security offering nutritional supports to pregnant women, lactating mothers, children under the age of 5 and as remedy against health abnormalities especially in developing countries ^{4, 5}.

Ocimum gratissimum L (Labiataeg) is popularly known as scent leaf belonging to the family Lamiaceae. It is predominantly found in Asia, South America and Africa ^{6, 7}. In Nigeria, O. gratissimum is commonly used as a spice in the preparation of soup, stew and its aqueous or ethanolic leaf extract is often employed in folklore medicine in treatment of some diseases ⁷. For example, the leaf extract of O. gratissimum is used in ethnomedicine in the treatment and management of bacterial infections, fever, diarrhea, respiratory-tract infections, pneumonia, coughs and diabetes ⁷. The chemical characterization of O. gratissimum revealed the presence of the following bioactives; α–pinene, β-pinene, 1,8-cineole, Terpineole, Eugenol, (E)-β-Caryoplyllene, Muurolere, Sehirene and β -selinerel ^{8, 9}. Essential oils including eugenol, 1, 8-cineole and linalool, thymol, citral, linalool, ethyl cynnamate and geraniol have been reported present in O. gratissimum ⁹. Interestingly, these oils from O. gratissimum have been reported to possess bactericidal effects against Escherichia coli, Staphyloccocus aureus, Bacillus subtilis ¹⁰ and fungicidal properties against Aspergillus repens, Curvularia lunata, Fusarium moniliforme, Aspergillus niger, Mucor mucedo, Fusarium solani, Botryodiplodia theobromae and Rhizopus solani ^{10, 11}. Researchers have reported various biological activities of O. gratissimum including wound healing potential ¹², antioxidant ¹⁰, anti-inflammatory ¹³, antihelmintic ¹⁴ and hepatoprotective properties ¹⁵.

Solanum aethiopicum L. is a seasonal plant which belongs to the family Solanaceae. It is popularly known as garden egg or scarlet eggplant. Solanum aethiopicum is evenly distributed in Asia, Africa (Nigeria, Cameroon, Sierra Leone, Zimbabwe and Ethiopia), Brazil, and Southern Europe ^{16, 17}. In a similar role as O. gratissimum, the leaves of S. aethiopicum are used to prepare yam porridge, soup and stew. Morphologically, the leaves are alternately arranged, oval shaped and wavy margined having about 10 to 30 cm long and a range value of 4 to 15 cm wide. Komlaga et al. ¹⁸ reported high contents of crude fibre, calcium, iron, zinc, protein, fat, vitamins and phytochemicals on the leaves of Solanum aethiopicum. In ethnomedicine, myriads of ailments such as anaemia, constipation, overweight, inflammation, swollen joints and ulcers have been treated using S. aethiopicum ^{17, 19}. Ocimum gratissimum and Solanum aethiopicum are considered as nutritional plants, but there is no published work that compared their nutritional compositions. Therefore the aim of this study was to evaluate the phytochemical, proximate and mineral compositions of Ocimum gratissimum and Solanum aethiopicum.

2. Materials and Methods

Fresh leaves of Ocimum gratissimum and Solanum aethiopicum were purchased from Eke Okigwe, Okigwe Local Government Area of Imo State, Nigeria. The leaves were authenticated by a plant taxonomist at University of Nigeria Nsukka as Ocimum gratissimum with herbarium number UNH No 360 and Solanum aethiopicum with herbarium number UNH No 331.

The identified leaves were destalked and air-dried differently for eight (8) days. After this time, the dried samples were differently homogenized using an auto-milling machine.

The tested phytochemical parameters: Alkaloids, saponins, flavonoid, phenols, oxalate and phytate were quantified using the methods described by Harborne ²⁰, while tannin was spectrophotometrically quantified by Folin-Denis methods described by Shabbir et al. ²¹

The proximate compositions; crude protein, crude fibre, crude lipid, ash, moisture and carbohydrate contents were determined according to the methods of the Association of Official Analytical Chemists ²².

Mineral constituents including calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), iron (Fe²⁺), and zinc (Zn²⁺) were determined using Atomic Absorption Spectrophotometry, while sodium (Na⁺) and phosphorus (P) were determined using a flame photometer ²².

Data presented are triplicate values ± SD. The mean and standard deviations were calculated using Excel package 2010. The values were subjected to Students’ T-test using GraphPad prism statistical software at probability level of 0.05.

3. Results

The comparative phytochemical composition of leaf extract of Ocimum gratissimum and Solanum aethiopicum is shown in Table 1. There were significant (p<0.05) increase in the percentage composition of alkaloid, saponin and phytate present in Solanum aethiopicum compared to Ocimum gratissimum. On the other hand; tannin, flavonoid and phenols were significantly more (p<0.05) in Ocimum gratissimum than Solanum aethiopicum.

Table 2 shows the results obtained from the percentage proximate compositions of the dried leaf extract of O. gratissimum and S. aethiopicum. From the result, all the proximate parameters were significantly higher (p<0.05) in O. gratissimum than in S. aethiopicum. The result also revealed higher moisture content (84.33 %) in S. aethiopicum.

Table 3 shows the results obtained from the percentage proximate compositions of the dried leaf extract of O. gratissimum and S. aethiopicum. From the result, all the tested mineral constituents (Ca²⁺, Mg²⁺, K⁺, Na⁺, P, Fe²⁺, Zn²⁺) were significantly higher (p<0.05) in O. gratissimum than in S. aethiopicum.

4. Discussion

Various parts of Ocimum gratissimum and Solanum aethiopicum are employed in ethnomedicine in the management of different diseases including diabetes, pile, rheumatism and hypertension ^{23, 24}. In addition, the leaves are recommended for people with anaemia and low iron especially during pregnancy and post-delivery. Therefore, this study evaluated the phytochemicals, proximate and mineral compositions of leaf extracts of O. gratissimum and S. aethiopicum.

Phytochemicals or plant secondary metabolites (PSMs) are chemicals associated with plants, which are not produced for the growth and development of plants. They are often synthesized for defence and protection. PSMs offer medicinal advantages to the cell due to their active ingredients ²⁵. The phytochemical compositions of O. gratissimum revealed a decreasing trend in tannin > saponin > phenol > oxalate > alkaloid > phytate. Comparatively, significant (p<0.05) increase were observed in the percentage compositions of alkaloid, saponin and phytate in Solanum aethiopicum compared to Ocimum gratissimum, while tannin, flavonoid and phenols were significantly greater (p<0.05) in Ocimum gratissimum than Solanum aethiopicum. Alkaloids are groups of plant secondary metabolites that have nitrogen as their elemental constituent. Traditionally, alkaloids act as anti-ulcer, anti-inflammatory and antibiotics agents ^{26, 27}. No wonder several researchers have reported its bactericidal and analgesic potentials ^{28, 29}. Saponins are glycosylated triterpenoids eliciting antifungal activities. This is owed to their detergent-like properties by distorting cell membranes of the fungal pathogens ³⁰. Again, they play significant role in the synthesis of steroid hormones ³¹. Tannins have stringent characteristics with strong affinity for proline (imino acid) capable of interfering with protein synthesis ³². Flavonoids have antioxidant properties. Thus, it prevents oxidative stress that may arise from reactive oxygen species (ROS) ^{29, 33}. Phenols and flavonoids are free radical scavengers. Their presence in plant may lend credence on the use of such plant in the management of cancer, Alzheimer’s disease and atherosclerosis ³⁴. The appreciable number of phytochemicals present in these plants suggested that O. gratissimum and S. aethiopicum have antioxidants, anti-cancer and antiallergic activities ³³, fungi-static and fungicidal properties ³⁰.

The results of proximate analysis revealed significant increase (p<0.05) in percentage proximate composition of O. gratissimum compared to S. aethiopicum. However, S. aethiopicum had higher moisture content (84.33 %) than O. gratissimum (8.99) (Table 2).. Proximate analysis is carried out to quantify the protein, crude fibre, lipid, ash, moistures and carbohydrate contents of a food sample ³⁵. Moisture content is used in evaluating the shelf life of food. Moisture availability is one of the factors that contribute to microbial growth ³⁶. The recorded higher moisture content in S. aethiopicum suggested a lower shelf-life than O. gratissimum. Carbohydrate in food offers nutritional support by providing energy, endurance, poor mental function and stamina ³⁷. The body system needs Adenosine Triphosphate (ATP) to drive cellular activity. This study suggested that ingestion of O. gratissimum and S. aethiopicum could act as source of ATP to the cell due to the presence of carbohydrate found in the plant samples. Proteins are macromolecules having several amino acid compositions. They help in repairing and replacing of worn out tissues ²⁹. Crude fibres are polysaccharides usually non-hydrolysable capable of increasing faecal bulk. When ingested, help in increasing gastro-motility and promoting a healthy digestive system ³⁸. Again, it also helps in alleviating the risk associated with colon cancer ²⁹. Ash content in food has a direct relationship with mineral constituents ³⁹. This implies the higher the ash content, the more nutritional the plant would be. The present result showed that O. gratissimum and S. aethiopicum are nutritionally sound and could solve the problems associated with constipation due to its high crude fibre.

The results of mineral compositions of the tested leaf samples revealed higher mineral compositions including Ca²⁺, Mg²⁺, K⁺, Na⁺, P, Fe²⁺, Zn²⁺ in O. gratissimum than S. aethiopicum. Calcium cation (Ca²⁺) helps in the maintenance of strong bones and teeth. It is significantly involved in muscular activity ⁴⁰. Magnesium cation (Mg²⁺) is a divalent inorganic ion found in the cell which has been implicated in cardiac rhythmical activity. It helps in the dilation of arteries and hence, decreases blood pressure ^{41, 42}. Sodium ion (Na⁺) as well as potassium ion (K⁺) is responsible for co-transport and also play role in communication between neurons. Sodium ions (Na⁺) help molecules cross through the membrane (co-transport). It also plays a role in the absorption of glucose in the small intestine ⁴³. Iron (II) ion (Fe²⁺) plays role in carrying oxygen. It is a key for oxygen transport in haemoglobin, which is mainly found in red blood cell. Traditionally, O. gratissimum and S. aethiopicum have been used in the treatment of anaemia. This may be owed to the significant presence of iron (II) ion present in these plant samples. Oboh et al. ¹⁶ have reported the haemolytic activity of Solanum macrocarpon. Zinc ion (Zn²⁺) is a crucial micronutrient involves in human growth and immune cellular response. It also acts as cofactor ²⁹. Zinc deficiency manifests in a number of ways including thin brittle nails, low sense of taste and smell, alopecia, increased susceptibility to disease and infection, slow healing and recurring colds ^{29, 42}. These results suggested that O. gratissimum and S. aethiopicum are enriched with mineral and could meet up with the required daily allowance of some of the investigated minerals when consumed adequately.

5. Conclusion

In conclusion, the study revealed that there is a significant increase (p< 0.05) in all the tested proximate and mineral compositions recorded in O. gratissimum when compared to S. aethiopicum. These suggested a higher nutritional composition in O. gratissimum than S. aethiopicum.

The study also showed that the leaf extracts of O. gratissimum and S. aethiopicum could be used in fortification and supplementation of other food samples. Therefore, increase consumption of these leaves will help alleviate the scourges associated with malnutrition in the population.

The result also justifies the use of O. gratissimum and S. aethiopicum in ethnomedicine as an anti-anaemic tonic in the treatment and management of anaemia condition due to its appreciable iron (II) ion (Fe²⁺) values.

References