ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

ABSTRACT
Colocasia esculenta 1. Schott belongs to the family Aracea and is grown for its edible
corms as a staple food throughout subtropical and tropical regions of the world
Amadumbe (the Zulu name for Colocasia esculenta) is consumed by and holds an
important place inthe diet oflocal rural people in Kwazulu-Natal, South Africa.
Three Amadumbe phenotypes were evaluated for their nutritional qualities. Like all
known tubers, the locally grown Amadume contained high carbohydrate levels,
adequate protein and low lipid content. Essential fatty acids (linoleic and linolenic)
were identified as components of the Amadumbe lipids. Amadumbe was generally
low in mineral content, apart from potassium and magnesium levels that were
relatively high. Some anti-nutrients (protease inhibitors, lectin, phenolic compounds,
alkaloids, oxalates, phytates, cyanogens and saponin) present in Amadumbe were also
identified and quantified The anti-nutrient levels were generally low and thus may
not pose an immediate effect on the health of consumers. Reduction of the anti­
nutrients through processing (cooking, frying, roasting) was observed to enhance the
nutritional value of these tubers. However, their presence suggests that a steady
consumption may lead to toxic levels.
Two proteins (AI and B2) with a-amylase inhibitor activity, and a steroidal saponin
(gamma-sitosterol) were extracted and partially characterised. The a-amylase inhibitors
were extracted and partially purified through ammonium sulphate precipitation and
chromatographic fractionation on diethylaminoethyl (DEAE)-Sephacel and Sephadex
G-lOO. The molecular weights of the two inhibitors were estimated to be 17 000 and
19 000 dalton, respectively. The inhibitors were fairly heat-stable, with optimum
activity at 40° C, pH 6.0. Both inhibitors showed activity against mammalian a­
amylases, but were devoid of activity against fungal amylases. Inhibitor A also
showed activity against plant amylases.
The steroidal saponin extracted from Amadumbe was characterized through TLC,
HPLC, GC-MS, IR and NMR spectroscopic analysis and identified to be gamma-
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