ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

The cyanogen levels for Amadumbe tubers from the three different localities are higher
than HCN levels for potato and sweet potato (0.005 mg/loo g and 0.004 mg/100 g
respectively), as well as for yam (0.06 mg/loo g) [Noman et al., 2007; Bbandari and
Kawabata, 2006]. Total cyanide levels in roots increase in a year oflow rainfall owing to
water stress on the plant (Bokanga et al., 1994). The total cyanide content of plant
parenchyma is dependent on the cuItivar and location, as well as on a variety of other
factors (Cardoso et al., 2005). Processing Amadumbe was highly efficient in substantially
reducing the cyanogens to low levels.
The reduction ofhydrogen cyanide through boiling may be because free cyanide and bond
cyanide are both water soluble and, hence, may be leached out during boiling. The heat
treatment involved in roasting and frying may have caused the vaporization of the free
cyanide (Udensi et al., 2007). The results indicated that the cyanogen levels found in the
processed and unprocessed tubers studied were satisfactorily below the safety level for
cyanide poisoning. For humans, the lethal dose ofHCN taken by mouth is estimated to be
ouly 0.5 to 3.5 mglkg body weight (Bradbury, 1991). However, smaller amount of
cyanogens could have several long-term adverse effects on hmnan health (Bhandari and
Kawabata, 2004; Okolie and Osagie, 1999). It has been reported that higher intake of
cyanogens could result in the development of neurological disease in hmnans
(Montgomery, 1980). The results obtained showed that although the cyanogen content
showed a relative decrease during processing, the amount remaining might be slightly
toxic to people who consume high quantities of Amadumbe tubers.
The saponin content ofthe studied samples was found to be higher than reported saponin
levels for Jatropha curcas L. (Martinez-Herrera et aI., 2006) and for citrus-fruit peel
(Oluremi et al., 2007). Gahlawat and Sehgal (1993) stated that loss of saponins during
processing might signify their thermolabile nature, resulting in structural changes.
Khokhar and Chauhan (1986) also mentioned that reduction of saponins may be due to
the formation ofa poorly extractable complex between them and sugar or amino acids.
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