INTRODUCTION

Launaea taraxacifolia (Compositae) commonly known as Dandelion is a member of the family Asteraceae. It is a plant found mainly in the Tropics. It is a perennial herb of about 150 cm tall with a creeping root system. The plant has an erect stem with the leaves at the base in a rosette form or alternate position capped by golden yellow flowers (Burkill, 1985; Agyakwa and Akobundu, 1998; Sakpere and Aremu, 2008).

Launaea taraxacifolia has been used for centuries as a remedy for various ailments such as skin and eye diseases-conjunctivitis, yaws, measles and diabetes mellitus and also rubbed on the limbs of toddlers to facilitate walking (Ayensu, 1978; Adebisi, 2004; Obi et al., 2006). The leaves of L. taraxacifolia plant are fed to nursing cows to stimulate lactation and also to sheep and goat to induce multiple births. The leaves of L. taraxacifolia have been reported to have hypolipidaemic effect and also ability to treat water retention disorders (Wichtl, 1994; Adebisi, 2004).

Dandelion leaves are used as common vegetable and eaten as salad or cooked in soups and sauces by Ghanaians. Over the years, several studies have revealed that wild or semi-wild plants are nutritionally important because of high vitamins, minerals, proteins, essential fatty acids and fibre contents (Asibey-Berko and Tayie, 1999; Jimoh and Oladiji, 2005; Okwu and Josiah, 2006; Ejoh et al., 2007; Iniaghe et al., 2009; Namrata et al., 2011; Prasad and Bisht, 2011). Even though L. taraxacifolia leaves are used as food, there is paucity of information about their constituents’ that make them nutritious and also exhibit their medicinal properties. The aim of this study was to determine the phytochemical and nutrient composition of L. taraxacifolia leaves and thus amass data to support and encourage its usage in human nutrition and in disease treatment.

MATERIALS AND METHODS

Plant collection: Fresh plant leaves were collected from the University of Cape Coast farms in August, 2010 and authenticated by Botanist at School of Biological Sciences Herbarium, University of Cape Coast, Ghana. The fresh plant material was then washed under running tap water, air dried, ground into a fine powder and stored in air-tight containers at 4°C.

Plant extraction: About 10 g of pulverized air dried leaves of L. taraxacifolia, was mixed with 100 mL of 70% ethanol in a conical flask, plugged with cotton and then kept on a shaker for 48 h. The mixture was then filtered and the solvent was evaporated using rotary vacuum pump. The crude extract obtained was stored in an air-tight desiccator for further analysis.

Determination of pH: About 10 g of the dried sample was transferred into a bottle with a screw cap and 25 mL of distilled water was added. The suspension was shaken for 15 min on a mechanical shaker after which the pH was measured (Udoh and Ogunwale, 1986).

Phytochemical screening: Phytochemical tests on the leaves of L. taraxacifolia were carried out on both the crude ethanolic extract and the ground powder using standard procedures as described by Sofowora (1993), Harborne (1973) and Evans (2002).

Proximate analysis: The estimation of the various food parameters namely moisture content, total ash, crude fat, crude fibre, crude protein and total carbohydrate on dry matter basis were carried out according to standard procedures using 50 g of dried powdered sample. In crude protein determination, Nitrogen was determined by Kjeldahl method (Pearson, 1976) and converted to protein by multiplying by a factor of 6.25. Moisture content, crude fat, crude fibre and total ash were determined by AOAC (1984) and to determine the total carbohydrate, the method of James (1995) based on difference was employed using the equation:

Total carbohydrate = 100-[%crude protein+ %crude fat+ %crude fibre+ %crude total ash]

Determination of energy or calorific value: The total energy value in the leaves of L. taraxacifolia in kcal/100 g was estimated using the method described by FAO (2003) as shown below:

Energy value = [% crude proteinx4.0] + [% crude fatx9.0] + [% carbohydratex4.0]

Mineral analysis: Test for the presence of minerals was carried out after acid digestion. The supernatant was decanted and the liquid was analyzed for the levels of Ca, Cu, K, Mg, Mn, Na, Fe, P, Co and Se using standard procedures. Sodium and potassium were determined using a flame photometer. Phosphorus level was determined using the Vanadate/molybdate yellow colour method by Allen and Deitz (1953). Calcium, magnesium, copper, chromium, zinc, iron, cadmium and lead levels were analyzed using Atomic Absorption Spectrophotometer. In order to avoid various interferences in the determinations, the mixtures were made to contain the same acid concentration. To overcome potential interference when determining Ca and Mg, a modifier 1% Lanthanium (w/v) was added to the final sample dilution and/all standards and blank which served as releasing agent. In the determination of Na, K, ionization interferences were dealt with by adding Caesium to both the sample and the standard. The concentration or level of each element in the sample solution was determined by reference to a calibration curve.

RESULTS AND DISCUSSION

The phytochemical screening of L. taraxacifolia leaves (Table 1) reveals the presence of tannins, saponins, steroids, flavonoids, cardiac glycosides and terpenoids. The reported health benefits of L. taraxacifolia leaves may be attributed to these phytoconstituents that might be of medicinal value. In this study, L. taraxacifolia leaves did not show the presence of alkaloids, anthraquinones, reducing sugars and cyanogenic glycosides. Cyanogenic glycosides and anthraquinones are very poisonous metabolites and their absence in the leaves of L. taraxacifolia makes it safe to be eaten by humans.

The proximate analysis of L. taraxacifolia leaves revealed that it contain an appreciably high amount of proteins (26.67%) (Table 2). This means that every 100 g of Launaea leaves would contain 26.67 g of protein. The crude protein content obtained in this study is higher when compared to 6.30% in water Spinach, 4.60% in Momordica foetida leaves, 11.29% in balsam apple leaves (Hassan and Umar, 2006), 24.85% in sweet potatoes leaves (Oduro et al., 2008). However, the crude protein of Launaea taraxacifolia leaves was found to be lower compared to 27.51% in moringa olefera leaves (Oduro et al., 2008), 29.78% in Piper guineeses and 31.00% in Talinum triangulare (Akindahunsi and Salawu, 2005). The RDA for protein is in the range 28-65 g for children, lactating mothers, pregnant women and adults. Launaea leaves can provide about 41-95% of RDA thus makes it good to be added to our diet as salads and sauce.

This study revealed that the moisture content (22.18%) of Launaea leaves (Table 2) is higher than those of some common leafy vegetables such as Xanthosem sagittifolum (14.7%), Adansonia digitata (9.5%), but lower compared to Gnetum buchholsianium (33.8%), Vernonia amygdaline (27.4%) (Ladan et al., 1996) and 76.53% in Moringa oleifera leaves (Oduro et al., 2008). The moisture content gives an indication of water soluble vitamins present.

The total ash content of 21.22% for Launaea leaves which is relatively high gives an indication to the rich source of inorganic minerals element that may be present in the leaves.

Table 1:	Result of the phytochemical screening Launaea taraxacifolia leaves
+: Present; -: Absent. Assays were all carried out in triplicates

Table 2:	Proximate composition of launaea taraxacifolia leaves on dry matter basis
Values expressed as % Mean±SEM, n = 3

The value obtained is higher compared to 1.8% reported in sweet potato leaves (Asibey-Berko and Tayie, 1999), 7.13% in Moringa oleifera (Oduro et al., 2008), 5% in Tribulus terrestris leaves, 19.61% in Amaranthus hybridus leaves (Nwaogu et al., 2000), 10.83% in water spinach leaves and 18.00% Balsam apple leaves (Hassan et al., 2004).

The study also revealed that there was a good amount of fibre (15.05%) in the leaves an indication that it can serve as a good source of fibre which might aid digestion, help reduce serum cholesterol level, risk of coronary heart disease and hypertension (Ganong, 2003). The crude fibre content of Launaea leaves is high compared to 7.20% in sweet potatoes leaves, 13% in Tribubus terrestris leaves but low compared to 19.25% in Moringa oleifera leaves (Oduro et al., 2008), 29.00% in balsam apple leaves (Hassan and Umar, 2006). The RDA for fibre is 18 - 35 g that means L. taraxacifolia can provide about 43-84% of the daily fibre requirements of the body.

The total carbohydrate content of L. taraxacifolia leaves was found to be 30.56%. The carbohydrate content of the leaves is considerably low compared to some other leafy vegetables like Tribulus terrestris 55.67%, 54.20% in water spinach leaves and 75% in sweet potato leaves (Asibey-Berko and Tayie, 1999), 43.88% in moringa oleifera (Oduro et al., 2008) and 82.8% in Corchorus tridens leaves (Asibey-Berko and Tayie, 1999). This relatively low carbohydrate content makes it suitable to be eaten when one wants to lose weight.

The fat content of L taraxacifolia was found to be 6.50% which is lower than 11% in water spinach leaves, 12% in Senna Obtusfolia, but higher when compared to spinach leaves (0.3%), Chaya leaves (0.4%) and 1.60% in Amaranthus hybridus leaves (Nwaogu et al., 2000) and 2.23% for moringa oleifera (Oduro et al., 2008). Crude fats are the principal sources of energy. One gram of lipid provides 9.0 kcal (37.33 kJ) of energy (FAO, 2003) which indicates that 100 g of Launaea taraxacifolia leaves lipid should provide about 58.5 kcal (244.76 kJ) of energy.

The estimated total energy value in the leaves of Launaea per 100 g was 287.47 kcal/100 g (1202.78 kJ/100 g) of the dry sample (Table 2). This value is low compared to the daily energy requirement of 2500-3000 kcal (10460-12552 kJ) for adults (WHO/FAO, 1985). The value is higher than 133.34 kcal/100 g (557.90 kJ/100 g) reported by Amata (2010) for leaves of Myrianthus arboreus. However, lower compared with 248.8-307.1 kcal/100 g (1040.98-1284.91 kJ/100 g) reported in Nigerian vegetables (Isong et al., 1999; Ihedioha and Okoye, 2011) and 316.66-329.76 kcal/100 g (1324.91-1379.47 kJ/100 g) for sweet potatoes and 305.62 kcal (1278.71 kJ) per 100 g for Moringa oleifera leaves (Asibey-Berko and Tayie, 1999; Oduro et al., 2008). The low calorific value of L. taraxacifolia leaves is an indication that it can be recommended to individuals suffering from overweight and obesity.

The inorganic mineral analysis of Launaea taraxacifolia leaves showed that it contained magnesium, sodium, potassium, calcium, phosphorus, manganese, iron, zinc and copper. These minerals were found in the order; Potassium > Calcium > Sodium > Magnesium >Phosphorus > Iron > Manganese > Zinc > Copper. However, cobalt and selenium were not detected, this indicates that these minerals are not present in a detectable amount in the leaves and this could be of great advantage to the consumers, since some of these minerals like cobalt and cadmium have been reported to be highly toxic even at low concentrations (Asaolu et al., 1997).

The potassium content of Launaea taraxacifolia 5067.30 mg/100 g in this study is higher compared to 6.42 mg/100 g found in Diospyros mespiliformis, 42.74 mg/100 g in Mucuna flagellipes (Ihedioha and Okoye, 2011) and 220.00 mg/100 g in cassia siamea leaves (Hassan and Ngaski, 2007). The level was above the range reported in some green leafy vegetables consumed in Sokoto, Nigeria (Ladan et al., 1996).

The sodium content of Launaea leaves 485.00 mg/100 g (Table 3) is high compared to 5.00 mg/100 g reported in Tribus terrestris leaves (Hassan et al., 2005), 3.29 mg/100 g in Mucuna flagellipes (Ihedioha and Okoye, 2011) and 45 mg/100 g in Senna obtusfolia (Lintas, 1992) and 95-320 mg/100 g reported for leaves of some wild edible plants from India (Seal, 2011). The RDA for Na is 500 mg which means that Launaea leaves can provide 97% of RDA for an adult. The Na and K are important in our diet due to the role in blood pressure regulation (Yoshimura et al., 1991). Na/K ratio of less than one in our diet is recommended hence, Launaea leaves with Na/K = 0.10 is good and adequate use of the leaves as vegetables in diets of hypertensive patients could be useful in lowering their blood pressure.

The calcium content in the leaves Launaea taraxacifolia is 2306.560 mg/100 g (Table 3) is high compared with the calcium content of 3.05 mg/100 g of Diosypyros mesipiliformis (Hassan et al., 2004), 941 mg/100 g in Momordica balsamina L. leaves (Hassan and Umar, 2006) and 17.95 mg/100 g in Cassia siamea leaves (Hassan and Ngaski, 2007) and 313.30 mg/100 g in Mucuna flagellipes (Ihedioha and Okoye, 2011). Calcium is needed for growth and maintenance of bone, teeth and muscles thus, Launaea taraxacifolia can contribute a meaningful amount of dietary calcium.

The phosphorus content of the Launaea taraxacifolia leaves 67.89 mg/100 g is high when compared to Diospyros mespiliformis 1.0 mg/100 g, 5.72 mg/100 g in Mucuna flagellipes (Ihedioha and Okoye, 2011) but low compared to 180.00 mg/100 g in Cassia siamea leaves (Hassan and Ngaski, 2007), 166-460 mg/100 g found in some green leafy vegetable consumed in Sokoto (Ladan et al., 1996). Calcium and phosphorus are the minerals present in the largest quantity in the structure of the body and bones.

Table 3:	Mineral composition of Launaea taraxacifolia leaves
ND means not detected. Values expressed as Mean± SEM, n = 3

Nieman et al. (1992) considered a food source good if the Ca/P is above 1 and poor if the ratio is less than 0.5. Launaea taraxacifolia leaves which had a Ca/P = 33.98 (Table 3) is therefore a good source of Ca and P needed in maintenance of bones, teeth and muscles (Turan et al., 2003).

The magnesium content of Launaea taraxacifolia leaves is 408.00 mg/100 g (Table 3) which is high compared to 2.56 mg/100 g in Diospyros mespiliformis (Hassan et al., 2004), 23.18 mg/100 g of Amaranthus hybridus leaves (Nwaogu et al., 2000), 112.73 mg/100 g in Mucuna flagellipes (Ihedioha and Okoye, 2011) and 400.00 mg/100 g in Cassia siamea leaves (Hassan and Ngaski, 2007).

Copper plays a role in haemoglobin formation and it contributes to iron and energy metabolism. The copper content of Launaea is 1.37 mg/100 g (Table 3) which is higher compared to 0.01 mg/100 g in Diospyros mespiliformis (Hassan et al., 2004), 1.28 mg/100 g in T. terrestris leaves (Hasan et al., 2005), 1.33 mg/100 g in Mucuna flagellipes (Ihedioha and Okoye, 2011) and 0.50 mg/100 g in Cassia siamea leaves (Hassan and Ngaski, 2007).

The zinc content of Launae leaves of 4.95 mg/100 g (Table 3) was found to be higher compared to 0.02 mg/100 g in Diospyros mespiliformis (Hassan et al., 2004), 0.10 mg/100 g in T. terrestris leaves but lower when compared to 6.85 mg/100 g in Cassia siamea leaves (Hassan and Ngaski, 2007). It was found to be in the range for Mucuna flagellipes leaves (2.24-8.52 mg/100 g) reported by Ihedioha and Okoye (2011). The value of Zinc obtained for Launaea leaves implies it’s a good source of zinc.

Manganese is another microelement essential for human nutrition. It acts as a cofactor of many enzymes (McDonald et al., 1995). The Manganese content in Launaea leaves is 5.82 mg/100 g which is lower than 11.6 mg/100 g in Momordica balsamina leaves (Hassan and Umar, 2006) but higher than lettuce of 0.3 mg/100 g and cabbage (0.2 mg/100 g) (Turan et al., 2003).

The iron content of Launaea leaves is 40.05 mg/100 g (Table 3) which is higher than 2.80 mg/100 g in T. terrestris and in some cultivated vegetables such as spinach (1.6 mg/100 g) lettuce (0.7 mg/100 g) and cabbage (0.3 mg/100 g) (Turan et al., 2003) but lower than 70.00 mg/100 g in Cassia siamae (Hassan and Ngaski, 2007), 84.4 mg/100 g in Helminthostachys sp. and 57.08 mg/100 g for Mucuna flagellipes leaves (Ihedioha and Okoye, 2011). The RDA value for iron is 10-15 mg (Nieman et al., 1992), this means the leaves of Launaea can contribute more than twice of iron to the RDA. This shows that about 50 g of Launaea can provide the daily iron requirement. The use of Launaea leaves in our diet could help in boosting the blood level especially in anaemic conditions.

CONCLUSION

The results of the present study revealed that the leaves of Launaea taraxacifolia contain certain phytochemicals namely tannins, saponins, flavonoids, cardiac glycosides, steroids and terpenoids which may account for its reported medicinal benefits. It also has appreciable amount of macronutrients and micronutrients. These results indicate that the leaves of Launaea taraxacifolia contained essential nutrients which can compete favourably well with other conventional edible leaves.

RECOMMENDATION

The recommended use of Launaea taraxacifolia leaves could help fulfil the growing demands of plant-based foods for human nutrition. Research is ongoing in our laboratory to quantify the levels of vitamins, identify the essential and non essential amino acids, to determine the effect of different storage conditions on nutrient composition and also to determine the effects of intake of Launaea leaves on disease conditions such as dyslipidaemia.

ACKNOWLEDGMENT

The authors are grateful to the Department of Biochemistry, School of Biological Sciences, University of Cape Coast for support in terms of provision of reagents and chemicals needed in carrying out this research work.