Sequestration Function of Complex Phosphates in Food Applications

Sequestration of metal ions by condensed phosphates is an important function of complex phosphates in food applications. In its most general definition sequestration is the elimination of chemical effects of metal ions initially dissolved in aqueous media. Sequestration generally refers to the formation of a stable, water-soluble complex with a metal ion that prevents the ion from participating in reactions. Orthophosphates can be said to reduce the effect of hardness ions (e.g., Ca⁺², Mg⁺², Fe^+2/+3, etc.) by precipitation, but this is not strictly sequestration. Sequestration requires a complex phosphate since it needs at least two separate sites of attachment on the same molecule.

The ability of a particular polyphosphate to sequester a particular metal ion is a function of pH, temperature, and the other species that are present. The sensitivity of the sequestration capacity to pH value of a polyphosphate decreases with increasing chain length.

Sequestration is best understood with respect to water softening and reducing scale.

Reference to the original papers is recommended for those interested in the subject (Van Wazer and Campanella, 1950; Van Wazer and Callis, 1958; Thilo, 1955; Irani and Callis, 1962; Irani and Morgenthaler, 1963). The sequestration of cations in foods is strongly associated with the inhibition of certain reactions involving metal ions like catalysis of lipid oxidation or enzymatic browning. Because of the flexible polyphosphate backbone and the presence of many anionic "sites" polyphosphates can accommodate the "needs" of many different cations in forming complexes with them (Table 4).

Ref:
Food Additives
2nd Ed. Revised and Expanded
by LUCINA E. LAMPILA and JOHN P. GODBER
Chapter 25, paragraph E, page 819