Distribution of Iodine in Iodine-Enriched Egg Yolk Fractions

Abstract

In order to clarify the iodine distribution in iodine-enriched eggs, Na125I (0.7mCi) was orally administered to egg-laying hens and 125I uptake was examined. Radioactivity (125I) was found predominantly in the egg yolk rather than in the egg white (approximately 30 times more radioactivity per gram).The components of the egg yolk were fractionated by various methods, and the ratios of 125I radioactivity in each fraction to the total radioactivity were calculated. Iodine distribution was about 18% in the protein fraction, about 8% in the lipid fraction and about 74% in the water-soluble fraction as determined by extraction with Folch's solvent, and its distribution was about 15% in the protein fraction, about 24% in the lipid fraction and about 61% in the water-soluble fraction as determined by extraction with butanol. The egg yolk was suspended with 1% sodium chloride, and lipoproteins in the egg yolk were fractionated into 7 fractions by ultracentrifugation. The iodine distribution was less than 1% in the precipitable fractions [lipovitellin fraction (fr 1), phosvitin fraction (fr 3) and γ-livetin fraction (fr 7)] and 5-55% in the supernatant fractions (frs 2, 4 and 6). When each fraction separated by ultracentrifugation was further fractionated with Folch's solvent, 80-90% of iodine was found in the aqueous fraction of all lipoprotein fractions except for lipovitellin fraction.Thus, iodine in the iodine-enriched egg yolk was distributed widely in protein, lipid and aqueous fractions, but was mostly present in the aqueous fraction as a low-molecular-weight substance which was not precipitated by ultracentrifugation.