ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

B1.1.1 Introduction
CHAPTER Bl-l: a-AMYLASE INIDBITOR (AI)
LITERATURE REVIEW
Many edible plant species consist of compounds that inhlbit enzymes, principally
hydrolases. Most of these inhibitors are proteins by nature, which particularly inhibit
enzymes by forming complexes that block the active site or modify enzyme
conformation, ultimately reducing the catalytic function. In the previous section (Section
A), a-amylase inhibitor activity was identified as one of the anti-nutrients present in
Amadumbe. In this section, a-amylase inhibitors in Colocasia esculenta will be isolated
from white Esikhawini tubers and partially characterized.
B1.1.2 a-Amylase inhibitor
Starch is a storage carbohydrate present in seeds and tobers of numerous plants (Teotia
et al. 200I). Starch consists oftwo components: amylose and amylopectin. Amylose is a
linear glucose polymer, which contains a-l,4 linkages and is a non branched polymer.
Amylopectin, on the other hand, is a highly branched polymer of glucose in which linear
chains of a-l,4 glucose residues are interlinked by a-l,6Iinkages [Buleon et aI., 1998].
Prior to starches being absorbed, they frrst need to be broken down into glucose and
smaller oligosaccharides. Digestive enzymes (amylase and isomaltase) are responsible
for this catalytic reaction (MarshaIl and Lauda, 1975; Choudbury et al., 1996).
Amylases (a-I,4-glucan-4-glucanohydrolases, EC 3.2.1.1) are a group of glycoside
hydrolases widely distributed in microorganisms, plants and animal tissues (Whitaker,
1988; Payan, 2004). a-Amylases hydrolyze long, complex, starch chain molecules to
release maltotriose and maltose from amylose and maltose, glucose and "limit dextrin"
from amylopectin (Moore et aI., 2005). Without calcium, the a-amylases which are
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