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Keywords:

  • black tea;
  • alkaloids;
  • phenolics;
  • plucking season;
  • processing;
  • HPLC

Abstract

The effects of two different rolling methods and three tea plucking seasons on alkaloids and phenolics, mainly flavan-3-ols and theaflavins, in black tea were studied using an improved high-performance liquid chromatographic method. Better separation of all tea compounds analyzed—the most important factor for their identification and quantitation—was achieved only with long elution gradients, which overcame the limitations of previously reported methods. Precision of the assay method was very high since intra-day and inter-day variations were within 0.76% and 1.66%, respectively. All analytes exhibited good linearity over the range evaluated with a correlation coefficient of 0.9987–1.000. Among the four solvents evaluated, 80% methanol was the most solvent for extracting individual tea compounds. The extraction method applied exhibited good repeatability (CV: 0.39–3.29%). The content of tea compounds analyzed varied with processing method and plucking season. Teas processed using the Cay-Kur method contained higher levels of identified phenolic compounds than orthodox teas, but their alkaloid content was similar to each other. The most abundant alkaloid in teas was caffeine, ranging from 17.84 mg g−1 dry weight in September plucking to 23.79 mg g−1 dry weight in May plucking. With respect to phenolic compounds, theaflavins were at the highest level, 14.27 mg g−1 dry weight, in Cay-Kur tea processed in May. Copyright © 2007 Society of Chemical Industry