Investigation by Response Surface Methodology of Extraction of Caffeine, Gallic Acid and Selected Catechins from Tea Using Water-Ethanol Mixtures

The simultaneous influence of pH and composition of water–ethanol mixtures on the extraction from tea of caffeine (CF), gallic acid (GA) and the selected catechins epicatechin (EC), epicatechin-3-gallate (ECG) and epigallocatechin-3-gallate (EGCG) is investigated by response surface methodology. Extraction experiments are carried out at room temperature according to a three-level full-factorial design in which pH, measured before mixing with ethanol, is varied between 6 and 8 and volume fraction of ethanol is varied between 30 and 70 % v/v. Response surfaces are determined by fitting of extracted amounts of the above substances, determined by HPLC analysis, with a second-degree polynomial model. Within the investigated experimental domain, extraction efficiency of CF is substantially the same and extraction of ECG and EGCG is not affected by acidity of the medium while both pH and composition influence the extraction of EC and GA.