A diet containing a high concentration of soy isoflavone was administered t
o laying hens and the contents of the isoflavones transferred to the plasma
and egg yolk were measured. A method for quantitatively measuring the conc
entration of isoflavone in the yolk was first established, before a high co
ncentration of soy isoflavone was administered to the laying hens over an 1
8-day period. The concentrations of isoflavone in the plasma and egg yolk r
eached their highest on the 12th day of the feeding period, the values bein
g 3,167 nmol/l and 65.29 mug/100 g, respectively. The concentration of chol
esterol in the yolk was slightly affected during the early stages of the fe
eding period. These findings clearly demonstrate that soy isoflavone was tr
ansferred into the yolk from the feed and that the cholesterol concentratio
n in the yolk was affected by administering the soy isoflavone-enriched fee
d.