Measurement of Estrogens in Cow's Milk, Human Milk, and Dairy Products

Abstract

Free natural estrogens in raw and commercial whole milk were quantitated by radioimmunoassay. The ranges of concentration of estrone, estradiol 17-.beta. and estriol were 34-55, 4-14 and 9-31 pg/ml. Proportions of active estrogens (estrone and estradiol) in the fat phases of milk by radioactive tracer on separated milk were 80 and 65%. These findings were supported by radioimmunoassay of skim milk and butter. Equilibrium dialysis of skim milk with hydrogen 3 labeled estrogens showed that 84-85% of estrone and estradiol and 61-66% of estriol were protein bound. Whey protein demonstrated a greater binding capacity than casein, as confirmed by radioimmunoassay of dry curd cottage cheese and whey. The concentrations in curd were 35, 11 and 6 pg/g. In whey they were 4, 2 and 3 pg/ml. The quantity of active estrogens in dairy products is too low to demonstrate biological activity. Butter was highest with concentrations of 539, 82 and 87 pg/g. Human colostrum demonstrated a maximum concentration of 4-5 ng/ml for estrone and estriol and .apprx. .5 ng/ml for estradiol. By the 5th day postpartum they decreased to become similar to cow''s milk.