Abstract
Selenomethionine (SeMet) is one of the main selenium forms in foods and supplements. Determining its presence in natural food samples creates difficulties due to possible oxidation processes. The objective of this study was to evaluate the possible degradation of SeMet in water extracts of green teas, one of the most consumed beverages worldwide. Such a medium has not been investigated at this time. The HILIC-HPLC MS/MS method with different stationary phases was used to achieve the satisfactory separation of SeMet and selenomethionine oxide (SeMetO). The addition of dithiothreitol and β-mercaptoethanol, recommended to ensure that SeMet is kept in the reduced form, was also evaluated. The best separation was achieved using the zwitterionic HILIC stationary phase coupled to mass spectrometry and MeOH with water (85/15, v/v) as the eluent. Extraction was done with hot water with the addition of β-mercaptoethanol. The infusions prepared from Lung-Ching teas (from the Zhejiang Province in China) contained the highest concentration of selenium in a typical cup of tea (12.5–17.3 µg L−1). For other tested teas it decreased in the following order: Yunnan > Dilmah > Lipton. For Lung-Ching teas, the sum of concentrations of SeMet and SeMetO corresponded to about 46–63% of the total selenium in their extracts.
Highlights
Selenium has been recognized as an essential nutrient for humans due to its role in antioxidant selenoproteins, which protect against oxidative stress, maintain intracellular redox status and take part in thyroid hormone production [1,2,3]
The objective of this study was to evaluate the possible degradation of selenomethionine in water extracts as such a medium has not been investigated at this time
The green teas from Zhejiang Province (Lung-Ching) showed the highest content of Se, ranging from 4.63 μg g−1 to 5.13 μg g−1, followed by Yunnan teas
Summary
Selenium has been recognized as an essential nutrient for humans due to its role in antioxidant selenoproteins, which protect against oxidative stress, maintain intracellular redox status and take part in thyroid hormone production [1,2,3]. Diet is a major source of selenium. Dietary sources of selenium vary from country to country [4,5]. The biological effect and bioavailability of selenium depend on the total ingested amount, and on its chemical form, accessibility and the presence of other dietary components [12,13]. The major selenium-containing amino acids occurring naturally in dietary sources are selenomethionine (SeMet) and Se-methylselenocysteine (MeSeCys) [14]. Both display strong antioxidant activities and cytotoxicity against several cancer cells [15]. Detailed knowledge on individual selenium species is important to their potential for human health and to understand the metabolic processes in plants
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