Abstract
The presence of antinutrients and toxic substances in vegetables limits the nutritional benefits of vegetables. The effects of age of plant and application of nitrogen fertilizer on the bioaccumulation of antinutrients (oxalate), toxic substances (cyanide and nitrate), micronutrients (vitamin C, β-carotene -provitamin A) and mineral elements (Fe, Mg, Cu, Zn, Ca Na and K) in Amaranthus cruentus wereinvestigated using pot experiment. Leaves were harvested at market maturity (vegetative phase) at three different leaf positions, basal (oldest), middle (younger) and upper (youngest) and were subjected to chemical analysis. Results obtained showed that cyanide, nitrate and oxalate were concentrated significantly in the basal and middle positions. The concentration of β-carotene, vitamin C and Zn were significantly higher in the leaves in the middle part than in the basal and upper leaves. Similarly, Fe, Mg, Cu and Na contents were significantly higher in the basal leaves than in the middle and upper leaves, while the concentration of K was higher in the younger leaves. We concluded that consumption of the vegetable leaves from the upper leaf position will provide the dietary requirements of the analysed micronutrients with significant reduction in the levels of oxalate, cyanide and nitrate and associated health problems. Key words: Amaranthus cruentus, market maturity, micronutrients, anti-nutrients, toxic substances, vegetable, oxalate, nitrate, cyanide.
Highlights
Amaranthus cruentus is an herbaceous annual leafy vegetable that can be produced for fresh market in 4 to 6 weeks after planting
We concluded that consumption of the vegetable leaves from the upper leaf position will provide the dietary requirements of the analysed micronutrients with significant reduction in the levels of oxalate, cyanide and nitrate and associated health problems
Plants growing under high nitrogen levels have high levels of cyanogenic glucosides and this explains why addition of nitrogen fertilizer resulted in higher levels of cyanide
Summary
Amaranthus cruentus is an herbaceous annual leafy vegetable that can be produced for fresh market in 4 to 6 weeks after planting. A. cruentus is rich in vitamins including β-carotene (precussor of vitamin A), vitamin B6, vitamin C, riboflavin and folate, and dietary minerals such as calcium, iron, magnesium, phosphorus, potassium, zinc, copper and manganese (Sussan and Anne, 1988). This vegetable is rich in lysine, an essential amino acid that is lacking in diets based on cereals and tubers (Schipper, 2000). The vegetable is known to contain some appreciable levels of cyanogenic glycoside which is a respiratory poison
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