ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

owing to the adverse effects ofhigh oxalate intake. Therefore, the reduced oxalate content
resulting from boiling Amadumbe tubers could have a positive impact on the health of
consumers, particularly as the reduction of oxalate levels with boiling is expected to
enhance the bioavailability ofessential dietary mineraJs in these tubers. Hence, boiling the
tuber would reduce the nutritional problems that the high levels ofoxa1ates could cause.
Levels of phytate in Amadnmbe were relatively higher compared to those found by
Huang et al. (2007) in taro. However, these levels were lower than the values reported for
cocoyam (Marfo et al., 1990). Generally, the phytic-acid conteJlt in these samples is
lower than those of other tropical root crops, including yam (Medoua et aI., 2007) and
cassava (Marfo et al., 1990). The phytate content of a plant could be determined by the
availability of phosphorus in the environment (Raboy and Dickinson, 1993; Buerkert et
aI., 1998). There are also other factors, such as environmental changes, genetics, locality,
soil types, irrigation conditions, year and fertilizer treatment that can affect the phytate
and phosphorus content (Dost and Tokul, 2006). The evident reduction in phytic acid
during cooking may be caused by leaching into the cooking medium, degeneration by
heat or the formation of insoluble complexes between phytate and other components,
such as phytate-protein and phytate-protein-mineral complexes (Vijayakumari et aI.,
1998; Siddhtrraju and Becker, 2001).
Cooking has been reported to lower the phytate levels in yam (Bhandari and Kawabata,
2006) and several plant foodstuffs (Vijayakumari et aI., 1997; Saikia et al., 1999; Badifu,
2001). The high content of phytate in the investigated Colocasia esculenta tubers is of
nutritional importance because the phosphorus of the phytate molecule is unavailable to
humans. Phytate also lowers the availability of many other necessary dietary minerals
(Siddhmaju and Becker, 2001). Therefore, the reduction of phytate in the Amadumbe
tubers is expected to enhance the bioavailability ofproteins and dietary minerals. There is
current support for the supposition that reduced levels of phytate may enhance health
through antioxidant and anticarcinogenic activity (Harland and Morris, 1995; Sirkka,
1997).
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