The Influence of Thiol Addition on Selenium Stability and Antioxidant Activity of Beetroot Juice

Determination of selenium species in food samples causes problems due to their possible oxidation and degradation. In this study, the stability of selenium compounds present in beetroot juices after addition of recommended thiols, such as ditiotreitol (DDT) or β-mercaptoethanol (βME), was evaluated. More total selenium was found in homemade freshly squeezed beetroot juice than in that sold as an organic juice. Furthermore, Se(IV) and selenomethionine oxide (SeMetO) were the main Se species found in both juices. During storage at different temperatures, the concentrations of selenomethionine (SeMet) and Se-methylselenocysteine (MetSeCys) decreased, while Se(IV) and SeMetO contents increased. The addition of DDT or βME, regardless their concentration, did not increase the concentration of SeMet at the expense of SeMetO decrease, as it was expected based on the literature data. Moreover, the used thiols affected the quantification of other selenium species, particularly Se(IV). The purchased organic beetroot juice showed higher ability to scavenge free radicals when it was stored at 4 °C.