Determination of Five Phthalate Esters in Tea and Their Dynamic Characteristics during Black Tea Processing

A highly specific and high extraction-rate method for the analysis of dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), diisobutyl phthalate (DiBP), and di-(2-ethyl) hexyl phthalate (DEHP) in tea samples was developed. Based on three-factor Box-Behnken response surface design, solid-phase extraction (SPE) of five phthalate ester (PAE) residues in tea was optimized. Optimal extraction conditions were found for extraction temperature (40 °C), extraction time (12 h), and ratio of tea to n-hexane (1:20). The dynamic distribution of PAEs at each stage of black tea processing was also analyzed, and it was found that the baking process was the main stage of PAE emission, indicating that traditional processing of black tea significantly degrades PAEs. Further, principal component analysis of the physicochemical properties and processing factors of the five PAEs identified the main processing stages affecting the release of PAEs, and it was found that the degradation of PAEs during black tea processing is also related to its own physicochemical properties, especially the octanol-water partition coefficient. These results can provide important references for the detection, determination of processing losses, and control of maximum residue limits (MRLs) of PAEs to ensure the quality and safety of black tea.