Materials and methods
Eight brands of black tea samples were procured from local
market and labeled as A–H. Tyrosinase was obtained from
Sigma Aldrich, USA. All solvents and chemicals used were
of analytical grade.
Preparation of black tea extract For each analysis, 1.5 g of
tea with 100 ml water was boiled for 10 min. The extract
was obtained by filtering the black tea through a cheese
cloth and the extract was used for various analyses.
Analysis of Tf and Tr by spectrophotometry Tf and Tr
analysis was carried out with the method described by
Roberts and Smith (1961). For the analysis of Tf and Tr, 4
solutions, Sol A, Sol B, Sol C and Sol D, were prepared as
presented below,