Effect of processing methods on some micronutrients, anti-nutrients and toxic substances in Vernonia amygdalina leaves

Abstract

Studies were conducted to investigate the effect of processing methods on antinutrients (soluble and total oxalates), toxic substances (cyanide and nitrate) and some micronutrients, vitamin C, β-carotene (vitamin A precursor) and mineral elements (Fe, Cu, Mg, Na and K) in Vernonia amygdalina. The processing methods used were boiling and sun drying. Results obtained showed that the nitrate content (1347.22 mg/kg) in the fresh vegetable is within the tolerable level and can be well tolerated in our meal. The cyanide level (199.11 mg/kg) is close to the maximum tolerable level of 200 mg/kg fresh weight. The levels of soluble and total oxalates in the fresh samples (2.80 g/kg and 4.76 g/kg respectively), were high enough to induce toxicity in human. All processing methods adopted significantly (p < 0.05) reduced the anti-nutrients and toxic substances in the vegetable. Boiling methods reduced the anti-nutrients and toxic substances significantly (p < 0.05) more than sun drying. The anti-nutrients and toxic substances decreased with boiling time. The processing methods also decreased vitamin C content significantly (p < 0.05) in the vegetable. Boiling methods retained more of the vitamin compared to sun drying. β-carotene levels increased in boiled vegetable, while its content was reduced in sundried sample. However, boiling exceeding 5 minutes led to reduction of the provitamin A content. Mineral elements also decreased with boiling. However, sun drying had no significant effect on the mineral contents of the vegetable. In conclusion, moderate boiling significantly reduces the levels of antinutrients and toxic substances while still conserving most of the micronutrients in amounts sufficient to meet our dietary requirements.