Optimization of extraction conditions for the maximum recovery of L-theanine from tea leaves: Comparison of black, green, and white tea

Background

The caffeine content of tea (Camellia sinensis (L.) Kuntze) can counteract the anti-anxiety effects of L-theanine. This study aims to find out the extraction method of L-theanine and caffeine from tea leaves to obtain the highest L-theanine and the lowest caffeine content. For this purpose, L-theanine and caffeine contents from three tea types (white, black and green) were extracted under different time and temperature conditions and their levels were determined in a single high-performance liquid chromatography (HPLC) analysis. Also, this study is the first to attempt to optimize the tea extraction conditions by maximizing the ratio of L-theanine to caffeine concentration.

Results

The results show that white tea extracted for 5 min at high temperatures (90–100°C) had the highest L-theanine level (21.52 mg/mL). Whereas, white tea, extracted for 5 min at low temperatures (10–11°C), had negligible caffeine (0.006 mg/mL). The caffeine content was relatively high in the extracts prepared from all types of tea under high temperatures (90–100°C). Whereas, caffeine level was low in tea extracted at low temperatures. The L-theanine-to-caffeine ratio was largest for white tea extracted at 10–11°C for 5 min (L-theanine/caffeine ratio > 200), and this ratio was lowest (0.96) for black tea extracted at 90–100°C for 30 min.

Conclusion

According to these data, the temperature and time of extraction have significant effects on the amount of L-theanine and caffeine extracted from Camellia sinensis (tea). In addition, white tea drinks prepared for 5 min at 10–11°C, could be recommended to people intolerant of caffeine side effects.