Rapid and selective quantification of l-theanine in ready-to-drink teas from Chinese market using SPE and UPLC-UV

An ultra performance liquid chromatography (UPLC) method combined with solid phase extraction (SPE) sample pre-treatment was developed and validated for the rapid quantification of l-theanine in ready-to-drink (RTD) teas. UPLC analysis of twenty-seven RTD teas from the Chinese market revealed that the l-theanine levels in various types of RTD teas were significantly different. RTD green teas were found to contain highest mean l-theanine level (37.85 ± 20.54 mg/L), followed by jasmine teas (36.60 ± 12.08 mg/L), Tieguanying teas (18.54 ± 3.46 mg/L) black teas (16.89 ± 6.56), Pu-erh teas (11.31 ± 0.90 mg/L) and oolong teas (3.85 ± 2.27 mg/L). The ratio of total polyphenols content to l-theanine content could be used as a featured parameter for differentiating RTD teas. l-theanine in RTD teas could be a reliable quality parameter that is complementary to total polyphenols.