Haze and tea cream generation is a serious problem in the production of ready-to-drink (RTD) black tea liquors. Such precipitates consist primarily of proteins and polyphenols. Tea protein and tea polyphenol have been separated successfully in this study. The interactions of (1) tea protein and mixed TF; and (2) tea protein and total tea polyphenol were studied by ITC. A series of techniques, including gel filtration chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis, CBB assay and fourier transform infrared spectroscopy (FTIR), have been used to determine the quantity and properties of proteins isolated from black tea powder. The molecular mass of the tea protein was detected to be approximately 11 kD at pH 5.0. The purity of this protein isolate was 51.4 wt % and a possible beta-sheet secondary structure was indicated from FTIR spectra. The total phenols in the tea polyphenol sample separated by Zn2+ precipitation under alkali conditions (pH 7.5) was increased to approximately 65 wt % of the sample tested. The binding mechanism of tea protein and TF was somewhat different from that of tea protein and total tea polyphenol, although both interactions were successfully fitted using a sequential sites binding model.
In black tea liquor production, polyphenols tend to interact with proteins, caffeine and metal cations to form colloidal suspensions of haze and "tea cream", which are detrimental to product appearance and taste. This is a key concern in the production of ready-to-drink (RTD; iced tea) beverages, which are typically made from reconstituted spray dried tea powders and stored at low temperatures (potentially leading to precipitation). Tea cream and haze are traditionally removed by dissolution through pH adjustment. The size of haze and tea cream aggregates means that membrane technology can offer an alternative nonchemical separation option.
To facilitate the removal of haze and tea cream in commercial RTD tea production, it is important to increase the level of understanding of polyphenol or tea protein interactions that occur in black tea liquor. Such interactions are the focus of this paper.