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Research Article
Nutritional Composition of Water Spinach (Ipomoea aquatica Forsk.) Leaves

K.J. Umar, L.G. Hassan , S.M. Dangoggo and M.J. Ladan
 
ABSTRACT
Analyses of the nutritional composition of water spinach (<I>Ipomoea aquatica</I>) Forsk leaves were carried out using standard methods of food analysis. The proximate composition as well as mineral elements were determined. The leaves were found on dry weight basis to have high moisture (72.83 ±0.29%), ash (10.83 ±0.80%), crude lipid (11.00 ±0.50%), crude fibre (17.67 ±0.35%) and available carbohydrate (54.20 ±0.68%), but low in crude protein content (6.30 ±0.27%). The leaves also have energy value (300.94 ±5.31 kcal/100 g) that is within the range reported in some Nigerian leafy vegetables. The mineral element contents were high with remarkable concentration of K (5,458.33 ±954.70 mg/100 g) and Fe (210.30 ±2.47 mg/100 g). Also the leaves content moderate concentrations of Na (135.00 ±2.50 mg/100 g), calcium (416.70 ±5.77 mg/100 g), Magnesium (301.64 ±12.69 mg/100 g) and P (109.29 ±0.55 mg/100 g), with low Cu (0.36 ±0.01 mg/100 g), Mn (2.14 ±0.22 mg/100 g) and Zn (2.47 ±0.27 mg/100 g) contents. Comparing the mineral content with recommended dietary allowance, it was showed that the plant leaves is good sources of K, Mn and Fe for all categories of people, while Mg is adequate enough for adult female and children. From the result,<I> Ipomoea aquatica</I> Forsk leaves could be used for nutritional purposes, due to the amount and diversity of nutrients it contains.
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K.J. Umar, L.G. Hassan , S.M. Dangoggo and M.J. Ladan , 2007. Nutritional Composition of Water Spinach (Ipomoea aquatica Forsk.) Leaves. Journal of Applied Sciences, 7: 803-809.

DOI: 10.3923/jas.2007.803.809

URL: http://scialert.net/abstract/?doi=jas.2007.803.809

INTRODUCTION

Green leafy vegetables have been recognised as rich source of micronutrients (minerals and vitamins) and antioxidants (Kala and Prakash, 2004). In most developing nations where food shortages and famine is mostly experienced, greens are the means of livelihood; Niger famine of 2005 is a clear evidence, in which many populace depend on leaves of Anza or Dilo (Boscia senegegalensis) and Roselle (Hibiscus sabdariffa) leaves as a means of survival. The roles played by leafy vegetables particularly during food shortage could probably be due to its being the first edible plant part to grow coupled with relative abundance compared to other plant parts used as a food item. This important feature demonstrated by the wild leafy vegetable attracts a lot of scientific research so as to assess their nutrients content. (Ogle and Grivetti, 1985; Ladan et al., 1996; Nordeide et al., 1996; Smith et al., 1996; Freiberger et al., 1998; Cook et al., 2000; Lockeett et al., 2000; Ogle et al., 2001; Faruq et al., 2002; Gupta et al., 2005).

Water spinach (Ipomoea aquatica Forsk) is a vascular semi-aquatic plant native to tropics and subtropics that grow wild and some time cultivated in Southeast Asia, India and Southern China (Gothberg et al., 2005). Water spinach is a herbaceous perennial plant belonging to the family Convolvulaceae. It has a long, hollow and viny stem, grow prostrate or floating and the roots are produced from the nodes and penetrate into wet soil or mud. The leaf shape ranges from saggitate to lanceolate (USDA, 2005; Gothberg et al., 2005; Wikipedia, 2005) Despite the use of this plant as food especially by the inhabitants of the area where this plant grows, no report was available on its nutritional content. Thus, this is the aim of this work with the following objectives.

To report the proximate composition of water spinach leaves
To report the mineral content of water spinach leaves
Compared the results obtained with other values reported in some species of Ipomoea and other green leafy vegetables.

MATERIALS AND METHODS

Sample collection and sample treatment: Sample of water spinach (Ipomoea aquatica) used in this study was collected along the bank of River Zamfara at Nassarawa, a village near Jega in Kebbi State, Nigeria. Prior to analysis, the plant leaves were separated from the stalk and washed with distilled water. The residual moisture was evaporated at room temperature. The leaves were then put in large paper envelopes and oven dried at 60°C until constant weight was obtained (Fasakin, 2004). The dried leaves were then ground in a porcelain mortar, sieved through 20 mesh sieve and stored in plastic container. The powdered sample was used for both proximate and mineral analysis. Moisture content was however, evaluated using fresh leaves.

Proximate analysis: The moisture content of I. Aquatica leaves were determined by drying ten leaves (in triplicate) in a Gallenkamp oven at 105°C until constant weight was attained (AOAC, 1990). Ash content was determined by dry ashing in Lenton muffle furnace at 525°C for 24 h. Crude protein content was calculated by multiplying the value obtained from Kjeldahl’s nitrogen by a protein factor of 5.3, a factor recommended for vegetable analysis (Bernice and Merril, 1975). Crude lipid was quantified by the method describe by AOAC (1990) using the Soxhlet apparatus and n-hexane as a solvent. Crude fibre was estimated by acid-base digestion with 1.25% H2SO4 (w/v) and 1.25% NaOH (w/v) solutions (AOAC, 1990). Available carbohydrates were calculated by difference i.e., total sum of crude protein, crude lipid, crude fibre and ash deducted from 100% DM (AOAC, 1990). The sample calorific value was estimated (in kcal) according to the formula: Energy = (g proteinx2.44)+(g lipidx8.37)+(g available carbohydratex3.57) (Asibey-Berko and Tayie, 1999).

Mineral analysis
Sample digestion:
One gram powdered sample was put in digestion flask followed by addition of 25.0 cm3 concentrated HNO3. The flask was then heated in Tecator digestion block until evolution of brown fume stopped. 1 cm3 of perchloric acid was added to the mixture and the content was further heated to a clear solution. After heating, 30 cm3 of hot distilled water was added to the digest and heated to boiling. The solution was then filtered hot into a clean 50 cm3 volumetric flask, cooled and made up to the mark with distilled water (Tayie and Asibey-Berko, 2001). Two more duplicate digest solutions and a blank were prepared.

Mineral quantification: The concentrations of Ca, Mg, Cu, Co, Fe, Mn and Zn in the digest were performed with an Alpha-4 model atomic absorption spectrophotometer with standard air-acetylene flame. The Na and K content was analysed by flame atomic emission spectrophotometry using corning 400 spectrophotometer. P was analysed with Jenway 6100 spectrophotometer using ammonium vanadate-molybdate colorimetric method (AOAC, 1990). For Ca and Mg determination, in order to avoid potential anionic interferences, 4 cm3 of 5% lanthanum chloride (LaCl3.7H2O) solution was added to 1 cm3 of the digest in a 50 cm3 volumetric flask and the solution made up to the mark with distilled water (Amaro-Lopez et al., 1999).

RESULTS AND DISCUSSION

Proximate composition: As shown in Table 1 the leaves moisture content (72.83±0.29%) was low when compared with value of 91% found in Vietnamese water spinach (Ipomoea aquatica) leaves (Ogle et al., 2001) and that of sweet potato (Ipomoea batatas) leaves (83.7-87.1%) (Asibey-Berko and Taiye, 1999; Ishida et al., 2000). The leaves moisture content was however within the range of 58.0-90.64% reported in some Nigerian green leafy vegetables (Ladan et al., 1996; Tomori and Obijole, 2000).

The high ash content of Ipomoea aquatica leaves (10.83±0.80%) is an indication that the leaves contain nutritionally important mineral elements. The value recorded in this study is low compared to 14.44% (on dry weight basis) in Ipomoea aquatica leaves grown in Vietnam (Ogle et al., 2001) and 17.87% found in leaves of Ipomoea sp. grown in Swaziland (Ogle and Griretti, 1985). In contrast, the value is higher than that of Ipomoea batatas leaves (1.8 g/100 g dry weight) reported by Asibey-Berko and Taiye (1999).

The crude protein content in Ipomoea aquatica leaves (6.30±0.27%) analysed is higher than that reported in Ipomoea aquatica leaves (4.25% dry weight) grown in Vietnam (Ogle et al., 2001). When compared with other species such as Ipomoea batatas leaves with crude protein content of 8.0% (Asibey-Berko and Taiye, 1999), 11.67-18.00% (Ishida et al., 2000) and 24.37-29.46% (Monamodi et al., 2003), the plant leaves analysed have low crude protein content. The value on the other hand, accord with the protein content for fresh vegetables (0.5-5.0%) as reported by Lintas (1992). Furthermore, the protein content of this plant leaves even though appear to be low, could make significant contribution to the dietary intake especially during pre-harvest period when domesticated food are in short supply.


Table 1:

Proximate Composition of Ipomoea aquatica Forsk Leaves

*The data are mean value±standard deviation (SD) of three replicates.
aValue expressed as % wet weight

Table 2:

Mineral composition of Ipomoea aquatica forsk leaves

* The data is mean value±standard deviation (SD) of three replicated, ** Source: Thangadari et al. (2001)

The sample crude lipid content (11.00±0.50%) is high when compared with the values of 0.74% (Asibey-Berko and Taiye, 1999) and 2.56-6.82% dry weight (Ishida et al., 2000) reported in Ipomoea batatas leaves, but within the range (8.5-27.0%) reported in some wild green leafy vegetables of Nigeria and Republic of Niger (Ifon and Bassir, 1980; Sena et al., 1998).

Similar to crude lipid, Ipomoea aquatica leaves have high available carbohydrate content (54.20%) comparable to 51.8% in Moringa stenopetala leaves (Abuye et al., 2003) and 52.85% (dry weight) found in Bauhenia purpurea (Raghuvanshi et al., 2001). The value obtained was higher than those found in some tropical green leafy vegetable such as fluted pumpkin, Telferia occidentalis (Akwaowo et al., 2000) and Ceratotheca sesamoides (Fasakin, 2004). Conversely, the sample value was lower than 75.0 and 82.8% found in Corchorus tridents and Ipomoea batatas leaves, respectively (Asibey-Berko and Taiye, 1999).

Ipomoea aquatica leaves have high crude fibre (17.67±0.35%) when compared to 3.7% found in Ipomoea batatas leaves (Asibey-Berko and Taiye, 1999), but lower than value of 45.70-46.05% (dry weigh) reported as dietary fibre in Japanese Ipomoea batatas leaves (Ishida et al., 2000). The value was also within the range of 8.5-20.9% found in some Nigerian vegetables (Ifon and Bassir, 1980). High fibre content in food causes intestinal irritation and lower nutrient bioavailability (Aletor and Adeogun, 1995; Plessi et al., 1999; Vadivel and Janandanan, 2000). Apart from negative effect, intake of fibre can stimulate weakening hunger, stimulating peristaltic movement, increasing excretion of bile acids, increasing moisture content of excrements, lower the serum cholesterol level, risk of coronary heart disease, hypertension, diabetes, colon and breast cancer (Gorecka et al., 2000; Ishida et al., 2000; Ramula and Rao, 2003).

The calorific values of most vegetables are low (30-50 kcal/100 g) (Devlin, 1982). The result obtained in Ipomoea aquatica leaves was substantial (300.94±5.31 kcal/100 g on dry weight basis), which was slightly higher than 288.3 kcal/100 g found in Ipomoea batatas leaves (Asibey-Berko and Taiye, 1999) and comparable to calorific content of two varieties of Gnetum africanum leaves, Asutan (307.1 kcal/100 g) and Oron (303.2 kcal/100 g) (Isong et al., 1999).

Mineral content: Table 2 shown that potassium content (5,458.33±954.70%) was higher than that of Ipomoea batatas leaves (750-4,953.49 mg/100 g dry weight) (Taiye and Asibey-Berko, 2001; Ishida et al., 2002; Monamodi et al., 2003); but lower than the amount reported in some Nigerian leafy vegetables such as Talinum trianglare (8,000 mg/100 g), Crassocephalum biafrae (6,500 mg/100 g) and Solanum nigrum (6,700 mg/100 g) (Smith, 1983). However the value was comparable to values obtained in leaves of Celosia argentea (5,200 mg/100 g) and Solanum aethiopicum (5,000 mg/100 g) (Smith, 1983). Sodium is associated with potassium in the body in maintaining proper acid-base balance and nerve transmissions (Setiawan, 1996). The concentration of this mineral element was found to be 135.00±2.50 mg/100 g DM, which was higher than those of Ipomoea batatas leaves (Taiye and Asibey-Berko, 2001; Ishida et al., 2002). This value was lower than the values reported in Talinum trianglare (248.8-280 mg/100 g) (Ifong and Bassir, 1979; Smith, 1983), Telferia occidentalis (229.1 mg/100 g), Amaranthus caudatus (427.9 mg/100 g), Amaranthus hybridus (258.9 mg/100 g) and Vernonia amygdalina (117.4 mg/100 g) (Smith, 1983). From the result it was shown that the concentration of potassium was far greater than that of sodium as also evenced from value in literature compared with. The high amount of potassium may be due to its abundance in Nigerian soil (Oshodi et al., 1999).


Fig. 1:

Comparison of mineral content of Ipomoea aquatica leaveas with recommended dietray allowances

The K/Na was also high (40.43). This is advantageous as potassium is only taken from diet unlike sodium which is added during cooking. Furthermore taken into consideration that potassium depresses while sodium enhances blood pressure, thus, high amount could be an important factor in prevention of hypertension and atherosclerosis (Yoshimura et al., 1991).

Calcium and phosphorous are associated with each other for development and proper functioning of bones, teeth and muscles (Dosunmu, 1997; Turan et al., 2003). The calcium and phosphorus content in the leaves sample were 416.70±5.77 mg/100 g and 109.29±0.55 mg/100 g respectively, which were low compared with the respective value in Ipomoea batatas leaves (9,300-19,300; 170-220 mg/100 g) as reported by Monamodi et al. (2003). The calcium content, however, was higher than that of Vietnamese Ipomoea aquatica leaves (101 mg/100 g) (Ogle et al., 2001) and leaves of Indian S. tubirosam (100 mg/100 g) (Singh and Garg, 2006). The phosphorous content on the other hand, was lower than that found in Indian Solanum tubirosam (237 mg/100 g). According to Guil-Guerrero et al. (1998), for good calcium and phosphorus intestinal utilisation, Ca/P ratio must be close to unity. Ipomoea aquatica leaves had a high ratio (3.81). This showed that the leaves are good sources of Ca over that of P; consequently the diet based on this leaves required to be supplemented with other food material rich in phosphorus.

Ipomoea aquatica leaves contain significant amount of magnesium (301.64±12.69 mg/100 g). High Mg concentration in these leaves is expected since Mg is a component of leaves chlorophyll (Dosunmu, 1997; Akwaowo et al., 2000). The value in this finding is higher than the Mg content of Ipomoea batatas leaves (79-107 mg/100 g) (Ishida et al., 2000). The leaves Mg is within the range reported in some green vegetables (Ladan et al., 1996).

Iron deficiency, according to World Health Organisation (WHO); affect about 3.7 billion people out of which 2 billion people are anaemic (Meng et al., 2005). In this analysis; an outstanding finding was made on iron content in the leaves of Ipomoea aquatica (210.30±2.47 mg/100 g), which is higher than the value of 16.67 mg/100 g reported when similar work was done in Vietnam (Ogle et al., 2001) and those of Ipomoea sp. (41.27 mg/100 g dry weight) and Ipomoea batatas leaves (36.69-147.87 mg/100 g dry weight) (Ishida et al., 200; Tayie and Asibey-Berko, 2001). However, Ladan and co-workers (1996) reported high iron content (110-325 mg/100 g) in some green leafy vegetables consumed in Sokoto. High iron content in green is more often than not, attributed to soil contamination (Gowda et al., 2004). However considering the site of sampling this factor could not probably be the cause but could rather be due to soil composition.

The concentration of copper (0.36±0.01 mg/100 g), manganese (2.14±0.22 mg/100 g) and zinc (2.47±0.27 mg/100 g) in this sample was low compared with that of Ipomoea batatas leaves (3.34-3.95, 4.83-10.03 and 3.95-6.86 mg/100 g), respectively (Tayie and Asibey- Berko, 2001; Ishida et al., 2002; Monamodi et al., 2003), but the zinc content was higher than that of I. aquatica leaves analysed by Ogle et al. (2001). Thus, adequate consumption of this plant leaves may help in preventing adverse effects of dietary deficiencies of these micronutrients. Inadequate intake of micronutrient is recognized as an important contributor to the global burden of disease (Black, 2003).

Nutritional significant of mineral elements is usually compared with the standard recommended dietary allowance. In this study, mineral content of Ipomoea aquatica leaves was compared with standard values of US recommended dietary allowances (Table 2). Figure 1, it showed that the plant leaves is good sources of potassium, manganese and iron for all categories of people, while magnesium is adequate enough for adult female and children assuming total assimilation of these minerals.

CONCLUSIONS

The results of the nutritional analysis shown that Ipomoea aquatica Forsk leaves, like other leafy vegetables are good source of plant fibre, carbohydrate and minerals (particularly K, Fe, Mg and Mn). The results suggests that the plant leaves if consumed in sufficient amount could contribute greatly towards meeting human nutritional requirement for normal body growth and adequate protection against diseases arising from malnutrition. From the result, Ipomoea aquatica Forsk leaves are recommend for continues used for nutritional purposes, considering to the amount and diversity of nutrients it contains. Chemical analysis alone however, should not be the exclusive criteria for judging the nutritional significance of a plant parts. Thus, it becomes necessary to consider other aspects such as presence antinutritional/toxicological factors and biological evaluation of nutrients content.

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