ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

a.-Amylase inhibitors could function as part of the defense mechanism in plants. In
leguminous plants (Giri and Kachole, 1998; Melo et al., 1999) and cereals (Franco et al.,
2000; Yamagata et al., 1998), the role of amylase inlnbitors as plant-defense proteins is
pronounced and has received much focus (Gatehouse et al., 1986; Farmer and Ryan,
1990). a-Amylases and proteinases are inactivated by these inlnbitors in the insect gut,
thereby acting as insect anti-feedants. This interaction is believed to make plants less
palatable. Indeed, it can even be lethal to insects. Thus, these inlnbitors present the plants
with some selective advantages.
Increasing natural defense mechanisms in plants can enhance agriculturaI activity and
food safety by decreasing intensive use of pesticides (Huang et al., 1997; Chen et al.,
1999). These inlnbitors, however, often show confined specificities: a given inhibitor
may inhibit the major digestive enzymes ofone insect species, but not ofanother (Morton
et al., 2000). This specificity has been widely investigated, with some inhibitors capable
of acting against insect a-amylases or against mammalian enzymes only (Franco et aI.,
2000). As a resuh, a-amylase inhibitors show potential for utilization in several fields,
including protection ofcrops, obesity and treatment ofdiabetes (Tormo et aI., 2006).
Diabetes mellitus is a metabolic disorder ofmultiple aetiology characterised by chronic
hyperglycaemia with disturbance of carbohydrate, fat and protein metabolism resulting
from defects in insulin secretion, insulin action or both (WHO, 1999). Glucose peaks
occur after the intake of a meal in animals. a-Amylase inhibitors can reduce these peaks
until the body is capable of processing the glucose. This is achieved by reducing the
speed with which a-amylase can convert starch to simple sugars. Breuer (2003) held that
this is especially important for diabetics who exhibit low insulin levels which hamper the
prompt removal of extracellular glucose from the blood. Ali et al (2006) observed that
reducing hyperglycaemia, using extracts of six selected Malaysian plants, after meals is
one therapeutic approach which could be adopted in the treatement ofdiabetes.
Clinical use of inhibitors of intraluminal a-amylase activity has appeal because, in
theory, controlled reduction of starch digestion could influence carbohydrate uptake in
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