Proximate, Mineral and Phytochemical Analysis of the Leaves of H. myriantha and Urera trinervis

MATERIALS AND METHODS

Plant materials: The vegetal materials were bought at the local Total market from Bacongo, South-Brazzaville on 20th October, 2010. The plant materials were identified by Makita from the department of Botany, Faculty of Sciences, Marien NGOUABI University and were authenticated by Nkouka Saminou from the National Herbarium of the Vegetal Research Centre of Brazzaville (ex-OROSTOM-Congo), where voucher specimens are conserved. The leaves were air-dried for 21 days and milled into a powder. The powder was stored under dry conditions before analysis.

Chemical analysis
Proximate analysis: The moisture content was determined by drying at 105°C in an oven, until a constant weight was reached. For total ash determination, the plant samples were weighed and converted to dry ash in a muffle furnace at 450 and at 550°C for incineration. The Crude fat content was determined by extraction with hexane, using a Soxhlet apparatus. All these determinations were carried out according to AOAC (1990). Kjeldahl method was used for crude protein determination. Carbohydrate content was determined by calculating the difference between the sum of all the proximate compositions from 100%. Energy values were obtained by multiplying the carbohydrate, protein and fat by the Atwater conversion factors of 17, 17 and 37, respectively (Kilgour, 1987).

Mineral analysis: Mineral analyses were carried out according to Martin-Prevel et al. (1984). Elemental analyses were carried out using an atomic absorption spectrophotometer and a flame photometer to determine calcium, sodium, potassium and magnesium content. Aluminum, iron and phosphorus were determined calorimetrically. The concentration of each element in the sample was calculated on a dry matter basis.

Preparation of extracts: Extraction of bioactive compounds was carried out in the solvent mixture ethanol-chloroform according to the procedures described by Harborne (1998) and Biyiti et al. (1988). Twenty grams of air-dried, powdered sample was weighed and transferred into a beaker, then 300 mL of ethanol-chloroform (2:1) mixture was added and after agitation were allowed to extract at laboratory temperature for 24 h. The mixture was then filtered and the filtrate evaporated and concentrated using a boiling water bath. The solvent extracts thus obtained were submitted to phytochemical screening.

Preliminary phytochemical screening: Qualitative analysis was carried out following the methods described by Trease and Evans (1989); Harborne (1998) and Kokate (2001). The concentration of each compound was determined according to Mariita et al. (2010). Phytochemical analysis was conducted to determine the presence of alkaloids, anthraquinones, flavonoids, glycosides, tannins, triterpenoids, steroids and saponins.

RESULTS AND DISCUSSION

Proximate composition: The proximate composition of U. trinervis and H. myriantha leaves (Table 1) showed the highest moisture content value (62.90%) for U. trinervis while H. myriantha showed the lowest value (06.93%). The high moisture content of U. trinervis (62.90%) recorded in the present study was in line with the 59.16% recorded for some varieties of cassava (Megnanou et al., 2009) but it was significantly higher than the value ranged between 5.28 and 9.28% for some plant species (Dike, 2010) and the 5.9% for M. oleifera (Yameogo et al., 2011) which were favorably compared with that of H. myriantha (06.93%).

Table 1:	Proximate composition of the leaves

Table 2:	Mineral composition of the leaves

However, all the values found in the present study were lower than the 81.38% for B. oleracea (Kale) (Emebu and Anyika, 2011).

The carbohydrate content value of H. myriantha (60.02%) was significantly higher than that of U. trinervis (6.07%). However, the carbohydrate content value of H. myriantha was favorably compared with the 59.70% for E. guineensis (Dike, 2010), 62.94% for C. frutescens (Otunola et al., 2010) and 61.25% for V. mombassae (Emmanuel et al., 2011). This content value was found to be significantly higher than the 15.40% found in A. hybridus, the 30.40% in C. pepo and the 30.38% in G. africana (Iheanacho and Udebuani, 2009). It was also found to be lower than the 94.20% in T. triangulare (Dike, 2010) and the 89.45% in G. aqualla (Muhammad et al., 2011).

The high carbohydrate content of H. myriantha leaves suggest that they can be considered as a potential source of energy.

The result also showed that the leaves contained an appreciable and comparable amount of crude proteins (24.18 and 25.37% for U. trinervis and H. myriantha, respectively). The high protein content values recorded for both leaf types were found to be similar to the 24.90% for S. Africana but lower than the 33.21% for M. angolensis (Emmanuel et al., 2011) and the values ranged from 26.25 to 60.38% for mushroom species, except L. laccata (Egwim et al., 2011). However they were higher than 20.27 and 17.24% for F. asperifolia and F. sycomorus respectively (Nkafamiya et al., 2010). The high protein values recorded in this study suggest that the leaves can be ranked as a potential source of plant protein and therefore could be used as a protein supplement in the Congolese diet.

The fat content values of H. myriantha (1.54%) and U. trinervis (1.32%) were very low and found to be similar to 1.15% recorded in A. Digitata (Dike, 2010) and 1.70% in G. aqualla (Muhammad et al., 2011). These values were found to be very low when compared to the 24.0% recorded for A. senegalensis (Yameogo et al., 2011). The low fat content of the samples studied suggests that the plants cannot serve as oil vegetables but may be useful for individuals on weight-reducing diets (Emebu and Anyika, 2011).

The energy values of both samples were very high. That of H. myriantha (1508.32 kJ/100 g) was significantly higher than that of U. trinervis (562.19 kJ/100 g). This value was favorably compared to those reported for H. ulmoides and V. ferruginea leaves (504.48 and 516.80 KJ/100 g, respectively) (Andzouana and Mombouli, 2011) but significantly higher than the 56.46 Kcal/100 g reported for Kale (Emebu and Anyika, 2011). The energy value of H. myriantha was higher than that reported for P. mildbraedii (1086.44 kJ/100 g) (Akinyeye et al., 2010) and would assure food security for Congolese children.

The ash content values of the samples (6.14 and 5.54% respectively) were favorably compared to the range of 5.43 to 5.75% reported for some edible woody plants (Emmanuel et al., 2011). However, these values were lower than the range of 17.44 to 33.60% for mushroom species (Egwim et al., 2011) and higher than the range of 0.38-1.9% for selected vegetables grown in Peshawar (Bangash et al., 2011).

The results showed that the leaves contained appreciable amounts of nutrients such as protein, energy and carbohydrate that determined the nutritional value of the leaves.

Mineral composition: The result of mineral analysis of the leaves (Table 2) indicated that the minerals detected were calcium, magnesium, potassium, sodium, iron, manganese and phosphorus. The leaves showed a high level of phosphorus content (18.97 and 18.73%) for U. trinervis and H. myriantha, respectively) followed by potassium (1.25 and 1.29%)while calcium and magnesium were detected in much lower amounts in both samples (0.21-0.29%). Sodium, manganese and iron were detected as trace elements (0.02-0.09%). Aluminum was not detected. Beside phosphorus, the result showed the low mineral level of the leaves. The phosphorus content of both samples was considerably higher than the 0.35% reported for S. rebaudiana leaves (Tadhani and Subhash, 2006) and the range of 0.17-0.23% for Nigerian sesame seeds (Obiajunwa et al., 2005). These content values were lower than the 25.70% recorded in Z. officinale (Adanlawo and Dairo, 2007). The potassium content values recorded in this study were in line with the 1.33% recorded in the leaves of H. ulmoides however these values were lower than the 4.39% in V. ferruginea (Andzouana and Mombouli, 2011). Further analysis of the results showed that the calcium, magnesium and Manganese, sodium and iron content values fell within the range of 0.05 to 0.53 % and 0.01 to 0.04% reported for rice, maize, millet grains (Kouakou et al., 2008) and H. ulmoides and V. ferruginea leaves (Andzouana and Mombouli, 2011), respectively.

Table 3:	Phytochemical constituents of the leaves
-: Negative result,+: Low concentration, ++: Moderate concentration, +++: High concentration

The iron and the manganese contents of both samples studied were lower than their RDA values (1.37 and 2.94 mg/day for males and females, respectively) according to FAO/WHO (1988). The potassium content in this study was higher than the range of the requirement of this element for animals (0.2-0.6% dry weight basis) (Kawo et al., 2009).

The plants contained nutritionally important minerals. It is suggested that the leaves can be recommended as part of the daily nutrition for Congolese population.

Phytochemical constituents: The phytochemical analysis (Table 3) revealed that alkaloids, cardiac glycosides, tannins, triterpenoids and steroids were present in both plant leaves. Flavonoids were not detected in H. myriantha while anthraquinones and saponins were completely absent in both plant leaves. The results showed that cardiac glycosides were present in a significantly high concentration in both samples. Alkaloids were detected in U. trinervis in a high concentration while H. myriantha showed the presence in high concentration of triterpenoids and tannins. However, flavonoids, tannins and also alkaloids were found in moderate amounts in U. trinervis and H. myriantha, respectively. As steroids in both the studied leaves, triterpenoids were detected as trace compounds in U. trinervis. Further analysis of the results showed that U. trinervis contained most of the tested phytochemicals, while H. myriantha contained appreciable amounts of these phytochemicals.

Plant foods contain constituents such as flavonoids, saponins, etc, which have been assessed for their biological effects (Krishnaswamy and Raghuramulu, 1998). For instance, Edeoga and Enata (2001) reported that alkaloids are powerful pain relievers, have an antipyretic action, a stimulating effect and can act as topical anesthetic in ophthalmology. Cardenolides have been used in the treatment of congestive heart failure (Oloyede, 2005) and cardiac arrhythmia (Ngbede et al., 2008). Tannins are known to have antiviral, antibacterial and anti-tumor properties. Terpenoids and steroids are known to possess antibacterial and antineoplastic properties (Oduro et al., 2009). The presence of secondary metabolites in the leaves suggests that their consumption could have a preventive effect on woman body and help to treat related diseases by providing indicated properties to the vegetables.

CONCLUSION

The study revealed that U. trinervis and H. myriantha leaves contained appreciable amounts of nutrients, such as phosphorus, energy, protein and phytochemicals. This indicates that the leaves are nutritionally important, since their consumption provides essential nutrients and non-nutrients need for human body health development and also contribute to the medicinal value of the leaves and thus might be of medicinal and industrial importance (Kunle and Egharevba, 2009). Therefore, the leaves could be recommended as a constituent of human diet in Congo with pharmaceutical potentials and health benefits to consumers.

ACKNOWLEDGMENTS

The authors thank Seraphim Sita, member of the Laboratory of DGRST (Pte-Noire, Congo) and Basile Antouo (DGI, Pte-Noire) for assistance to carried out analysis.