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Journal of Food, Agriculture & Environment Vol.7 (3&4) : 359-363. 2009
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Effect of cooking on the mineral and antinutrient contents of the leaves of seven accessions of Colocasia esculenta (L.) Schott growing in South Africa Muinat N. Lewu 1, Patrick O. Adebola 2 and Anthony J. Afolayan
1*
1
Department of Botany, University of Fort Hare, Alice 5700, South Africa. Plant Breeding Division, ARC-Vegetable and Ornamental Plant Institute, Private Bag X293, Pretoria 0001, South Africa. *e-mail:
[email protected]
2
Received 19 July 2009, accepted 8 October 2009.
Abstract The effect of cooking on the mineral and antinutrient contents of the leaves of seven accessions (UFCe1 - UFCe7) of Colocasia esculenta (L.) Schott growing in South Africa was investigated. Cooking significantly reduced the phosphorus, potassium and zinc contents. After cooking, calcium, magnesium, sodium and copper levels were not significantly different in almost all the accessions tested in the study. In contrast, cooking appears to increase the iron levels in all the samples, though this was not significant in most of the accessions. The manganese levels were also reduced with cooking in four accessions while UFCe3, UFCe6 and UFCe7 showed increase in manganese level after boiling. Generally, potassium and magnesium contents were reasonably high in all the accessions. High dietary potassium in humans plays a protective role against hypertension, stroke, cardiac dysfunctions, renal damage, hypercalciuria, kidney stones and osteoporosis. The results further indicate that the accessions are good sources of potassium, magnesium, sodium and calcium. Salts of these minerals are known to regulate the acid-base balance of the body. Boiling remarkably reduced the level of the anti-nutritional factors, thereby improving the food quality of all the accessions tested in this study. Boiling for 5 min led to 16-78% drop in oxalate level, 28 - 61% in tannin and 17 - 41% reduction in phytate contents in some of the accessions. Boiled C. esculenta leaves may therefore serve as a good source of iron. This may imply that the consumption of the leaves of cocoyam may increase the blood level and may therefore be recommended as a good food for anemic patients. Key words: Accession, antinutrients, cocoyam, Colocasia esculenta, mineral composition.
Introduction Cocoyam belongs to the family Araceae and is an ancient crop grown for its edible corms, cormels, leaves and for other traditional uses by subsistence farmers 1, 2. There are two edible species of cocoyam. Colocasia esculenta also known as Taro and Xanthosoma sagittifolium (L.) Schott which is commonly referred to as Tannia. Both are generally cultivated for their enlarged underground starch-rich corms and cormels called tubers. In addition, the tender leaves are also used as leafy vegetables 3. Like other green leafy vegetables, the main problem in the consumption of the leaves of taro is the presence of anti-nutritional factors. These factors may have adverse effects on health through inhibition of protein digestion, growth, iron and zinc absorption 4, 5. However, all parts of the raw taro plant are known to contain oxalate, a toxic compound, which must be destroyed by thorough cooking before eating 6. The presence of oxalate causes sharp irritation and burning sensation in the mouth and throat when tubers or leaves are eaten which is a major limiting factor to the consumption of this crop 7. In order to reduce the effect of antinutrients, proper processing before consumption is necessary. Generally, cocoyam leaves are consumed by humans after cooking, either by boiling, blanching, steaming, stewing, frying or pressure cooking. These methods are found to be effective in improving digestibility, increasing nutrient availability and also minimizing food-borne diseases 8.
Though, boiling can help to reduce the oxalate content in the leaves of this species 6, it may also reduce the nutritional value of food crops arising from significant losses and changes in major nutrients during cooking 9. In other parts of the world, the leaves of C. esculenta have been reported to be rich in nutrients, including minerals and vitamins such as calcium, phosphorus, iron, vitamin C, thiamine, riboflavin and niacin 10, 11. To the best of our knowledge, the leaves of cocoyams cultivated in South Africa are yet to be screened for chemical composition as well as anti-nutritional factors. In the areas where this crop is cultivated in South Africa, attention has only been paid to the tubers and not the leaves. This is because the crop has remained underutilized due to lack of awareness of its nutritional value by majority of the populace 12. Consequently, information on the nutritional composition of this vegetable growing in South Africa has remained scanty. This study, therefore, was aimed to find out the effect of cooking on the mineral and anti-nutritional contents of the leaves of seven accessions of C. esculenta growing in this country and to compare the information among the different accessions under study. The results obtained from this study may further provide information on the nutritional value of the leaves of this plant as well as the effect of cooking on its mineral and antinutritional contents.
Journal of Food, Agriculture & Environment, Vol.7 (3&4), July-October 2009
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Values with different superscript (uppercase) within the same column show significant differences (P
