Trace Monitoring of Goitrin and Thiouracil in Milk and Cheese
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Trace Monitoring of Goitrin and Thiouracil in Milk and Cheese Terenzio Bertuzzi 1 & Silvia Rastelli 1 & Annalisa Mulazzi 1 & Amedeo Pietri 1
Received: 16 November 2015 / Accepted: 10 March 2016 # Springer Science+Business Media New York 2016
Abstract Goitrin and thiouracil belong to the thyreostats, a group of compounds that inhibit the thyroid function; thyreostats can be divided into two main groups: naturally occurring compounds, mainly originated from glucosinolates, and xenobiotic (thyreostatic drugs) compounds, used as growth-promoting agents and performance enhancers in food-producing animals. Recently, thiouracil was detected at low levels in urine and cow milk samples and a natural origin due to ingestion of Brassicaceae-rich feed was demonstrated. Considering that the natural occurrence of both goitrin and thiouracil can be due to the same type of feeding for cattle, a liquid chromatography–tandem mass spectrometry (LC-MS/ MS) method for their simultaneous determination at trace levels in milk and cheese was developed. Then, a limited survey and a study to evaluate their carry-over from milk to curd and ripened cheese were carried out. For both compounds, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.07 and 0.20 μg L−1 in milk, and 0.05 and 0.16 μg kg−1 in cheese; the average recovery values were above 80 %. In milk, their incidence was very high (≥95 %); the maximum value was 3.6 and 8.7 μg L−1 for goitrin and thiouracil, respectively. In cheese, only thiouracil was detected at levels close to those in milk. During cheese-making, both compounds remained mainly in the whey; during ageing, goitrin content decreased quickly and it was never detected after 2 months of ripening.
* Terenzio Bertuzzi [email protected]
1
Food & Feed Science and Nutrition Institute, Faculty of Agriculture, Università Cattolica del Sacro Cuore, Via Emilia Parmense 84, 29122 Piacenza, Italy
Keywords Goitrin . Thiouracil . Milk . Cheese
Introduction Goitrin (5-vinyl-2-thioxazolidine) and thiouracil (4-hydroxy2-pyrimidinethione) belong to the group of thyreostats; this term is used to refer to a complex group of substances that inhibit the thyroid function (Vanden et al. 2009). These compounds are amphoteric, relatively polar thioamides, characterised with a low molecular weight and with a sequence nitrogen–carbon–sulphur (Fig. 1). Thyreostats can be divided into two main groups: naturally occurring compounds and xenobiotic (thyreostatic drugs) compounds, used as growth-promoting agents and performance enhancers in food-producing animals. The group of naturally occurring thyreostats mainly originates from glucosinolates, present in some plants of the Brassicaceae family. During cellular disruption of the plant tissue, the myrosinase, a βthioglucosidase enzyme, hydrolyses the glucosinolates with formation of several metabolites; among these, some thyreostatic compounds occur, as isothiocianates and oxazolidine-2-thiones (OZTs; an appropriate located βhydroxyl substituent on glucosinolate s
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