Natural estrogens in dairy products: determination of free and conjugated forms by ultra high performance liquid chromatography with tandem mass spectrometry

Natural estrogens are synthesized by mammals in different amounts depending on the developmental stage and pregnancy/pregnancy period, and they may pass into milk, where they are mostly present as glucuronated and sulfated forms. In modern dairy practices about 75% of milk is produced from pregnant cows, therefore the amount of hormones that may pass in milk could be of concern. While estrogen determination in milk has been deeply investigated, the individual determination of estrogens and their conjugated forms in dairy products has not been fully addressed. The aim of this work was to develop and assess a sensitive method, using the peculiar retention properties of graphitized carbon black, to extract natural free estrogens and their major conjugated metabolites, without any enzymatic cleavage, from yogurt, cheese and butter. The free and conjugated estrogens were eluted in two distinct fractions from the solid phase extraction cartridge and analyzed separately by ultra high performance liquid chromatography coupled to tandem mass spectrometry. Recoveries were higher than 80% for all the three sample typologies. The highest matrix effects were observed for butter, which was richest in lipid content, but was below 30%. A survey on some commercial dairy products suggests that production processes decrease estrogen content. This article is protected by copyright. All rights reserved.