ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

The ability of phytic acid to complex with proteins and particularly with minerals has
been a subject of investigation for several reasons, predominantly from chemical and
nutritional viewpoints. Phytic acid forms complexes with nutritionally important minerals
such as calcium, copper and iron (Fe z + and Fe 3 "). This reaction decreases the solubility of
the metals, which are therefore not readily absorbed from the intestine (Brune et aI.,
1989; Sandberg etal., 1993; Weaver and Kannan, 2002).
There is strong concern that reduced mineral absorption, owing to consumption of food
products rich in phytates, may lead to borderline malnutrition (Reddy and Pierson, 1994).
It has also been shown that calcium ions interact with protein and phytate to decrease the
solubility of proteins further (De Rham and Jost, 1979; Frokiaer et aI., 2001). As a
consequence, phytate has been shown to inhibit the proteolysis of a number of enzymes
(including pepsin, trypsin and amylases of the intestinal tract) important in digestion
(Vaintraub andBlIlmaga, 1991).
Certain functional properties of proteins, which are dependant on their solubility and
hydration, can be negatively affected by the reduced solubility of proteins as a result of
protein-phytate complex. Such hydrodynamic properties (viscosity, gelation) include
emulsifying capacity, foaming and foam performance, and dispersibility in aqueous
media (Urbano et al., 2000). Phytic acids may also affect the digestibility of starch.
Phytic acid and starches are structurally capable of combining via phosphate linkages
(Sirkka, 1997). Thus, adverse effects on the digestion ofstarches and proteins, as well as
reduced bioavailability of essential dietary minerals, are the result of high phytate
contents in tubers.
Investigators have shown that phytic acid may be beneficial with regard to human health,
including as an anti-cancer agent (soft tissue, colon, metastatic lung cancer, mammary
cancers) [Shamsuddin et al., 1997; Febles et al., 2002], as an inhibitor in renal stone
development (Grases et aI., 2000) and as an anti-oxidant agent. Phytic acid has an anti­
oxidative function because it chelates with iron by combining with all the available Fe
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