No abstract

Leafy vegetables generally contain some intrinsic phytotoxins that affect human health negatively at high concentrations. The presence of these toxins which is believed to protect the plant from their preys has severely limited the nutritional potential of vegetables. The reason that, this research was conducted to determine the effect of cooking (fresh leaves of the vegetable were cook or boiled for 5 and 10 minutes) and sun drying on antinutrients (soluble and total oxalates), toxic substance (cyanide and nitrate) and some micronutrients which include vitamin C, β-carotene (provitamin A) and mineral elements (Fe, Mg, Cu, Na and K) in Corchorus olitorius. Results obtained showed that cooking and sun drying significantly (p < 0.05) reduced the antinutrients and toxic substances in Corchorus olitorius except that the reduction in cyanide and total oxalate concentrations with sun drying were not significant (p > 0.05). Corchorus olitorius is an excellent source of β-carotene, vitamin C and some mineral elements. However, both treatments reduce vitamin C concentration significantly (p < 0.05). β-carotene concentration increased in the cooked Corchorus olitorius leaves, while its concentration was reduced in sundried leaves. However, cooking exceeding 5 minutes led to significant (p < 0.05) reduction in β-carotene concentration in the vegetables. Mineral elements (Fe, Cu, Mg, Na and K) in the Corchorus olitorius decreased significantly with cooking, whereas sun drying had no significant effect on the mineral concentrations. The results conclude that moderate cooking reduce the phytotoxins to the tolerable levels without compromising the nutritional values of the vegetable.

Pot experiments were performed to determine the effect of heading (fruiting) on antinutrients (soluble and total oxalates), toxic substances (cyanide and nitrate) and some micronutrients viz; vitamin C, β-carotene (provitamin A) and mineral elements (Fe, Mg, Cu, Zn, Ca, Na and K) in Amaranthus cruentus grown in nitrogen and non-nitogen treated soil. The vegetable leaves were harvested at both market maturity (vegetative phase) and heading (reproductive phase) and were subjected to chemical analysis. Results obtained showed that the vitamin C, cyanide, soluble and total oxalates concentrations in the vegetable were significantly elevated (p < 0.05) during heading irrespective of soil nitrogen levels. Nitrate and β-carotene concentrations decreased significantly (p < 0.05) during heading except that the decrease in β-carotene was not significant in vegetable treated with nitrogen fertilizer. Similarly the result also showed that the Mg, Zn, Ca and K concentrations were not significantly affected with heading. However, the Fe concentration was increased, while the Cu and Na concentrations were reduced significantly (p < 0.05) with heading.The result concludes that harvesting of Amaranthus cruentus at vegetative phase generally reduce the levels of most of the plant toxins and still conserve most of the micronutrients in an amount to meet our dietary requirements.

Pot experiment was conducted to determine the effect of leaf positions on the concentrations of some phytotoxins (cyanide, nitrate, soluble and total oxalates), micronutrients namely; vitamin C, β-carotene (provitamin A) and mineral elements (Fe, Mg, Cu, Zn, Ca Na and K) at vegetative phase of Telfairia occidentalis grown in nitrogen and non -nitrogen treated soil. The leaves of Telfairia occidentalis were harvested and analysed at three different leaf locations, namely; basal, middle and upper positions. The result obtained showed that no significant differences was observed in the cyanide concentration between basal and middle leaves and between middle and upper leaves, however, basal leaves had significant (p< 0.05) higher concentration of cyanide than upper leaves irrespective of soil nitrogen levels. The concentrations of nitrate and β-carotene in control and nitrogen fertilized Telfairia occidentalis were significantly (p<0.05) highest in upper, followed by middle and lowest in the basal leaf position. The soluble and total oxalates content in Telfairia occidentalis were significantly (p<0.05) higher in the basal and middle leaves than the upper leaves irrespective of soil nitrogen levels. While the vitamin C concentration in the vegetable was significantly elevated in basal leaves than the leaves obtain from middle and upper leaf locations. Analysis of mineral elements showed that Fe, Mg, Zn and Ca were concentrated more in the basal and middle leaves than the upper leaves while the K concentration was significantly (p<0.05) higher in the middle and upper leaves than the basal leaves in control and nitrogen treated Telfairia occidentalis. The results conclude that concentrations of most