Preparation of flavanol-rich green tea extract by precipitation with AlCl₃

The aim of this study was to use AlCl₃ in the extraction of green tea flavanols (GTFs) from longjing green tea and examine the factors that influence the yield of GTF extract. Dry tea leaves were soaked in hot distilled water and the infusion was obtained by filtration. To the tea infusion, varying amounts of AlCl₃ were added, causing precipitation of GTFs. After adjusting the pH to 4.0-6.5 and centrifugation, the yellow precipitate was collected. Sulphuric acid solution (40%) was then used to dissolve the GTFs from the yellow precipitate. The GTF solution was extracted using an equal volume of ethyl acetate. After the removal of ethyl acetate using a rotary evaporator, the GTF extract was redissolved in distilled water and the whole process was repeated. The resulting GTF extract was freeze-dried. It was found that the amount of AlCl₃ used and the pH and temperature of the precipitation mixture significantly affected the yield and purity of GTF extract. A yield of 9.6g extract per 100g dry tea leaves with GTFs>94% could be obtained if AlCl₃ was used in the ratio of 15g per 100g equivalent dry tea leaves and the pH of the precipitation mixture was adjusted to 5.5 at 30°C.