Evaluating the photocatalytic treatment of stevioside by TiO₂ in different aqueous matrices and identification of transformation products

The present study reports the photocatalytic transformation of stevioside, under simulated solar irradiation using TiO₂ as a photocatalyst. As a tool of investigating the effect of various aqueous matrices, as well as, the initial stevioside concentration on the variation of the photocatalytic efficiency, a fully nested experimental design was employed. A significant impact on the degradation rate of the sweetener was observed: degradation rate decreases in the order distilled water>river water>lake water, attributed to the increased natural organic matter content of the respective natural water samples. Moreover, the investigation has involved the identification of intermediate compounds, as well as the assessment of mineralization and toxicity evaluation. More than one hundred unknown transformation products, most of them in the form of several isobaric species, were identified. By employing accurate mass determination, we were able to attribute an empirical formula to each species and through MSⁿ analyses we were capable to distinguish several isobaric species. The overall transformation mechanism was assessed and involved the hydroxylation/oxidation of the molecule and the subsequent loss of the glucose units bound to the parent compound.