Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Abstract

Insight into the mineral, protein, phytate relationships in rice bran was gained by examining the solubility behavior of these components. Solubility profiles of the phosphorus and nitrogen components as a function of pH did not correspond, except in the pH 1.0-2.0 range. This is evidence that association between protein and phytate only occurred in this low pH range. Potassium, magnesium, and calcium solubilities as a function of pH corresponded to those of the phytic acid salts of these minerals. Soluble magnesium and potassium phytates were isolated on Sephadex G-25-50 and identified by ICP, confirming their presence in rice bran. The isolated soluble magnesium and potassium phytates had low metal to phytate ratios: approximately 2 magnesium molecules and 1 potassium molecule per phytate molecule at endogenous pH (7.1). The compositions of these soluble metal-phytate species were found to be pH-dependent. The number of molecules of magnesium and potassium associated per phytate molecule decreased with decreasing pH. No relationship between the soluble iron, zinc, or copper species and phytate were apparent from the pH data. However, a possible association of copper and zinc with protein in the pH 6-10 range was suggested by the behavior of their solubility curves. Increased amounts of Fe(II), Fe(III), Zn(II), or Cu(II) ions, added as sulfates to rice bran slurries, affected the solubilities of the endogenous minerals, proteins, and phytates. The data from these solubility studies along with the results of SDS gel electrophoresis, pH, and differential pulse polarography experiments provided evidence for: association of iron, zinc, and copper ions with the albumins leading to the formation of insoluble mineral-albumin complexes. ('31)P NMR was employed to examine the solution interactions of lithium and potassium ions with sodium phytate. The phytate molecular conformation was found to be pH and concentration dependent. The conformational equilibria of sodium phytate in aqueous solution was not affected by the addition of potassium ions, however, the phytate molecular conformation was influenced by added lithium ions and was dependent on lithium ion concentration. Furthermore, the phytate molecule showed some selectivity for lithium ion association over potassium and sodium ions.

Pages

217

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