Within this study, a new method enabling monitoring of various estrogenic substances potentially occurring in milk and dairy products was proposed. Groups of compounds fairly differing in physico-chemical properties and biological activity were analyzed: four natural estrogens, four synthetic estrogens, five mycoestrogens, and nine phytoestrogens. Since they may pass into milk mainly in glucuronated and sulfated forms, an enzymatic hydrolysis was involved prior to the extraction based on the QuEChERS methodology. For the purification of the organic extract, a dispersive solid-phase extraction (d-SPE) with sorbent C18 was applied. The final analysis was performed by ultra-high-performance liquid chromatography (UHPLC) coupled with triple quadrupole tandem mass spectrometry (MS/MS). Method recovery ranged from 70 to 120% with a relative standard deviation (RSD) value lower than 20% and limits of quantification (LOQs) in the range of 0.02-0.60 μg/L (0.2-6.0 μg/kg dry weight) and 0.02-0.90 μg/kg (0.2-6.0 μg/kg dry weight) for milk and yogurt, respectively. The new procedure was applied for the investigation of estrogenic compounds in 11 milk samples and 13 yogurt samples from a Czech retail market. Mainly phytoestrogens were found in the studied samples. The most abundant compounds were equol and enterolactone representing 40-90% of all estrogens. The total content of phytoestrogens (free and bound) was in the range of 149-3870 μg/kg dry weight. This amount is approximately 20 times higher compared to non-bound estrogens.

Departamento de Química Unidad Departamental de Química Analítica Facultad de Ciencias Universidad de La Laguna Avenida Astrofísico Francisco Sánchez s n° 38206 San Cristóbal de La Laguna Tenerife Spain

Departamento de Química Unidad Departamental de Química Analítica Facultad de Ciencias Universidad de La Laguna Avenida Astrofísico Francisco Sánchez s n° 38206 San Cristóbal de La Laguna Tenerife Spain Faculty of Food and Biochemical Technology Department of Food Analysis and Nutrition University of Chemistry and Technology Prague Technicka 3 166 28 Prague Czech Republic

Faculty of Food and Biochemical Technology Department of Food Analysis and Nutrition University of Chemistry and Technology Prague Technicka 3 166 28 Prague Czech Republic

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