THE NUTRIENT COMPOSITION OF SOME NIGERIAN LEAFY GREEN VEGETABLES AND PHYSIOLOGICAL AVAILABILITY OF THEIR IRON CONTENT

Abstract

Ten leafy green vegetables, commonly incorporated into diets by peasants of the Cross River State of Nigeria, have been analyzed for their various nutrient contents. The vegetables were Abelmoschus esculentus, Corohorus olitorius, Talinum triangulare, Amaranthus hybridus. Piper guineense, Ocimum basillicum. Curourbita pepo. Vernonia amygdalina, Telfaria occidentalie, and Marsdenia latlfolia. The investigations covered the analyses of the mineral (Na, K, Ca, Mg, Mn, Fe, Cu, Zn, S. P and CI), sugar (fructose, glucose, sucrose and maltose) constituents as well as the determination of the energy value of those vegetables. The moisture content ranged between 75% and 92% of fresh weight, indicating high dry matter (DN) in some of the vegetables. Ether extract and crude fibre contents were low in most of the vegetables ranging between 2.6% and 8.11% DM and 8.5% and 20.89% DM, respectively. The crude protein values of these edible leafy green vegetables were between 17.22% and 28.41% DM. These high values of crude protein coupled with the high protein/fibre ratios (0.84 to 3.26) suggest that most of the vegetables can be potential source of dietary protein. Atomic absorption spectrophotometric analyses revealed the presence of a wide spectrum of mineral elements in the vegetables. The potassium (1.43% - 6.10% DM), Calcium (1.06% - 3.62% DM), Iron (0.03% - 0.59% DM) Sulphur (0.23% - 0.59% DM), and Phosphorus (0.24% - 0.71%DM) contents were appreciably high. Analysis of the vegetable extracts showed that these vegetables contain appreciably high quantities of Riboflavin (0.46 me - 2.07 mg/100 g DM), Pyridoxine (1.08 mg - I.96 mg/100 g DM) and Ascorbic acid (20.72 mg - 160.17 mg/100 g DM), but generally low quantities of Thiamine (0.06 mg - 0.27 mg/100 g DM). Thus the daily dietary requirements for these vitamins and minerals can be met by consuming sufficient quantities of the vegetable. The low Thiamine value suggest the need for dietary augmentation from other sources. Paper chromatographic analyses of the ethanol soluble sugars showed the trend: Sucrose > Glucose > Fructose > Maltose. Energy values of the vegetables ranged between 1513.90 kj/100 g DM and 1961.33 kj/100 g DM. The low sugar and energy contents suggest the possibility of incorporating the vegetables into the diets of diabetic and obese patients. Studies were also carried out to assess the physiological availability of the vegetable iron to the consumer. The criterion used for the bioassay was the potency of the vegetable iron, relative to ferrous sulphate, in regenerating the haemoglobin in growing anaemic rats. The results showed that the relative availabilities of the vegetable iron ranged between 24% and 84%on the haemoglobin concentration scale or between 20% and 83% on the total haemoglobin. scale. These results suggest the possibility of using most of these vegetables for nutritional therapy and/or a preventive measure against iron deficiency anaemia, reportedly prevalent among women and children of the low income group, Studies on the influence of copper on iron metabolism have so far been limited to inorganic iron sources. Investigations were therefore carried out to assess the effect of copper on the availability of the vegetable iron. The criteria used were haemoglobin regeneration and tissue iron retention in iron, copper - deficient rats. The results showed higher haemoglobin regeneration but lower hepatic iron at higher level of dietary copper, thus demonstrating tissue iron mobilization for haemoglobin synthesis. The total iron retention in blood haemoglobin, liver and spleen increased with the level of dietary copper suggesting a possible enhancement of the absorption of the vegetable iron by dietary copper. Iron retention in the spleen showed a trend towards higher values at higher levels of dietary copper during iron repletion in the iron, copper-deficient rats. The results of these studies are discussed.