ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

A.l.4.2 Amylase inhibitors
In order to assimilate starches, which are complex storage carbohydrates, amylase (a
digestive enzyme) and other enzymes have to break them down (Choudhury et aI., 1996).
Through amylase [a-l,4-glncan-4-glucanhydrolase - Enzyme Code (EC) number
3.2.1.1], starch is broken down to maltose units, then to glucose monomer units. There
are plants which have proteinaceous a-amylase inhibitors, as well as proteinase inhibitors
(Fraoco et aI., 2000; Mello et al., 2002; Payan, 2004).
Several types ofplants, especially those in the legume family, have been used to extract
amylase inhibitors (Marshall and Lauda, 2006). A large number of sweet potato
genotypes have also been reported to contain a-amylase inhibitors (Sasikirao et al., 1999;
Rekha et al., 1999). Pancreatic and salivary amylase action is affected by amylase
inhibitors (Saunders, 1975; Pace et al., 1978) and faeces reflect this by evidencing a
greater proportion ofundigested starch. Pusztai et al. (1995) observed that the nutritional
quality of the food ingested consequently decreases, and Boivin (1987) surmised that
undigested starch in the colon because of high level of amylase inhibitors may cause
diarrhea.
Diabetes mellitus is a chronic disease, associated with abnormally high levels of glucose
in the blood, caused by an insufficient insulin production or lack of responsiveness to
insulin or both (WHO, 1999). A means of treating diabetes is through the reduction of
postpraodial hyperglycemia by activating decreased absorption of glucose in the
digestive tract. The action of carbohydrate-hydrolyzing enzymes, a-amylase and a­
glycosidase is inhibited to achieve this state, thus decreasing and delaying digestion of
carbohydrates. This leads to a reduction in the rate of glucose absorption and a
consequent decrease in plasma glucose after meals (Rhabasa-Lhoret and Chiasson, 2004;
Ali et al., 2006).
It has been claimed that a-amylase inlubitors assist weight loss, although initial research
showed them ineffective in reducing carbohydrate absorption (Bo-Linn et al., 1982;
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