| Abstract: | As part of a study of the reasons for the large effects of a small dietary supplement of methyl sterculate on the physical properties and lipid composition of hen's egg yolk, individual yolks from sterculate-fed hens have been examined. These yolks set to a firm gel on cooling in the range 20-0 °C, but there were large variations in eggs from different hens that were accompanied by variations in the proportion of saturated fatty acid residues in the yolk lipids. Gel formation was reversible on immediate rewarming but prolonged storage at low temperature caused irreversible alterations. Diluted yolk showed analogous changes in viscosity on cooling and provided a convenient model system for examining the effect of pH, ionic strength, and the action of trypsin. From these results it is concluded that the protein of the high-lipid low-density lipoprotein of yolk is directly involved in the gelation of the yolk. A series of eggs laid by one sterculatefed hen over 30 days showed large and possibly periodic variations in the lipid composition and gelation temperature of the yolks. These results and some data from other hens suggested that large variations in yolk properties accompany a high response to sterculate feeding. |
