ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

B.A.2.9 Alkaloid [Harborne (1973»)
5 g ofthe sample was weighed into a 250 ml beaker and 200 ml of10 per cent acetic acid in
ethanol was added, covered and allowed to stand for four hOUTS. The mixture was filtered
and the extract was concentrated, using a water bath, to one-quarter ofthe original volume.
Concentrated ammonium hydroxide was added dropwise to the extract until precipitation
was complete. The whole solution was allowed to settle and the precipitate was collected,
washed with dilute ammonium hydroxide and then filtered. The alkaloid was the residue,
which was dried and weighed.
B.A.2.10 Phytate determination [Mehlich (1953»)
2 g of sample material was extracted in 30 ml of double acid (0.05 M HCI and 0.025 M
HzS04) for three hours. Samples were filtered under vacuum through Whatrnan no 1 filter
paper. The following solutious were added to 5 ml ofthe extract:
• 50 ml 0.05 M sulfuric acid;
• 20 ml ammonium molybdate;
• 20 ml ascorbic acid;
• 10 ml potassium antimonytartrase (the ratio 5:2:2:1).
The mixture was allowed to stand for 30 minutes at room temperature to allow colour to
develop. The absorbance ofthe samples was measured spectrophotometrically at 820 nm. A
standard curve was prepared, expressing the results as a potassium hydrogen phosphate
equivalent. The concentration ofphytate was calculated from its phosphorus content.
B.Bl Isolation of amylase inhibitor
B.Bl.l Extraction ofColocasia esc:ulenta a-amylase inhibitor from tubers
Amadumbe tubers were obtained from the local market at Esikhawini in Kwazulu-Natal,
South Africa. Tubers were washed, peeled, cut into small pieces (2 cm x 3 cm) and dried
overoight at 40· C. The dried tubers were ground into flOUT, homogenized and defatted with
hexane, then filtered and air-dried. 20 g of the defatted flour was extracted for a-amylase
inhIbitor with 100 ml ofdistilled water containing I per cent polyvinylpolypyrrolidone (pVP).
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