Fe(III) - Galactomannan solid and aqueous complexes. Potentiometric, EPR spectroscopy and thermal data

Galactomannans can be employed in food industries to modify the final rheol ogical properties of the products. Since they are not absorbed by the livin g organisms they can also be used in dietary foods. The equilibria involvin g the interactions of Fe(III) and galactomannans and arabinogalactan of sev eral leguminous plants were characterized by potentiometric titrations and EPR spectroscopy. The log of the equilibrium constants for the formation of ML species, where M is the metal ion and L is the monomeric unit of the bi opolymers, were 15.4, 14.1 and 18.5, for the galactomannans of C. fastuosa, L. leucocephala and S. macranthera, respectively. Log K values for protona ted species (MHL) were 3.1, 3.3, and were not detected for the galactomanna n of S. macranthera. The log K values for the formation of ML2 were 14.1, 1 3.3 and 15.2, respectively. Early formation of insoluble products in the eq uilibrium with arabinogalactan and Fe(III) prevented acquisition of reliabl e data. The solid complexes assays showed a great dipolar interaction betwe en two Fe(III) ions in the inner structure of the biopolymer which increase d as the degree of substitution of the galactomannan decreased, and also sh owed the resulting thermal stability. The complexes impart a new possibilit y of providing essential metal ions in dietary foods since decomplexation o f the complexes can occur at different pH values existing in the human body .