Effects of infusion conditions and decaffeination on free amino acid profiles of green and black tea

Abstract

This study aimed to investigate free amino acid profiles of black and green tea infusions. Hydrophilic interaction liquid chromatography (HILIC) coupled to tandem mass spectrometry was used to analyze free amino acids in tea without any pre-column or post-column derivatization. A total 20 amino acids (18 proteinogenic and 2 non-proteinogenic) were determined in black and green tea samples. Sum of the concentrations of free amino acids in tea infusion after 2min of brewing process was 220.53mg/l and 211.21mg/l for black and green tea, respectively. It linearly increased reaching to 311.17mg/l and 277.43mg/l for black and green tea, respectively, within 15min of brewing at 85°C. Leaching rates were differed significantly for different individual amino acids. In general, hydrophilic amino acids leached into infusion faster than hydrophobic amino acids. Approximately 30% of total free amino acids in tea infusions after 15min of brewing was theanine. Partial decaffeination (>50%) of tea by means of supercritical carbon dioxide extraction resulted in 22% of reduction in total free amino acids in tea when water was used as co-solvent.