Assessing Caffeine Contents in Tea Infusions Decaffeinated by Hot Water Treatment Using High Performance Liquid Chromatography and Studying the Effects of Mint Leaf Addition to Tea Infusions on Improvement of their Total Polyphenol Contents

Background and Objectives: Due to the health concerns of people about caffeine, several techniques have been developed to remove caffeine from tea; however, these techniques include limitations. The objective of the present study was to remove caffeine from dried tea leaves using hot water treatment. Materials and Methods: Hot water treatment was used to decaffeinate green and black tea leaves using two stages of brewing. Caffeine of the tea infusions was extracted using liquid–liquid extraction technique and quantified using high performance liquid chromatography. Furthermore, pH, total polyphenol content and antioxidant activity were assessed using electronic pH meter, Folin-Ciocalteu method and ABTS method, respectively. Sensory evaluation was carried out using 5-point hedonic scale test. Tea infusions were prepared within two stages of brewing at 1, 3 and 5 min as primary and 7 min as total brewing times. Results: After 3 min of primary brewing time, decaffeination rates of Ceylon black, China green and Iranian green teas were assessed as 47.7, 81.55 and 85.99%. Antioxidant activity of these samples included 87.7, 85.99 and 81.55%, while total polyphenol content included 83.03, 44.44 and 37.7%, respectively. In general, pH and total polyphenol content of decaffeinated tea-mint infusions increased significantly. Conclusions: Effects of brewing time on caffeine concentration of the tea infusions were revealed in this study. In conclusion, hot water treatment is a safe method and includes a high efficiency for the decaffeination of green and black teas.