Comparative study on phenolic compounds of green tea (Camellia sinensis L.) prepared by different brewing methods

Abstract

Tea consumers’ choices are primarily influenced by taste, aroma, price, and brand while making tea selections; however, they are less likely to consider the phytochemical content and nutritional benefits of tea. Although studies on the phenolic content of green tea under various extraction conditions have been published, to the best of our knowledge, there are no studies on the impact of brewing duration and on the amount of phenolic compounds in the infusion. In this study, the effect of the amount of Turkish green tea (GT, 5-10 g) and brewing time (BT, 5-60 min) on phenolic compounds was evaluated using high-performance liquid chromatography (HPLC). According to the HPLC analysis of green tea infusions, 10 different phenolic compounds were determined: gallic acid (GA, 27.41-78.93 mg/L), gallocatechin (GC, 65.40-307.41 mg/L), catechin (C, 3.81-36.82 mg/L), epicatechin (EC, 177.29-366.71 mg/L), epigallocatechin gallate (EGCG, 645.85-1344.34 mg/L), epicatechin gallate (ECG, 16.60-44.81 mg/L), catechin gallate (CG, 0.245-0.564 mg/L), kaempferol (2.40-10.98 mg/L), quercetin-3-rhamnosylglucoside (Q3RG, 4.89-5.54 mg/L) and an alkaloid: caffeine (CAF, 390.63-785.79 mg/L). In addition, the total catechins and polyphenols were found to be in the range of 1325.00-2798.09 mg/L and 1357.31-2881.08 mg/L, respectively. It was observed that as the amount of green tea brewed increased, the phenolic compounds in the infusion increased in general, but this increase was not linear. There were variations regarding the caffeine and phenolic concentrations, which may be attributed to the brewing time. Therefore, it can be concluded that these compounds are exposed to degradation and/or epimerization as the brewing time increases.