Investigation of Black Tea Leave Pre-treatment by Microwave and Ultrasound to Extract Effective Compounds

In this paper, microwave and ultrasound irradiation were compared for pre-treating the black tea (Camelia Sinensis) leaves powder to increase the weight percentage of extraction yield of effectives compounds in multi stage solvent extraction (MSSE) via three stage extraction with distilled water. Maximum extraction yield by MSSE from the un-pretreated tea sample at optimum condition (135 min extraction time, 65°C extraction temperature and 25 ml/g solvent to solid ratio) was obtained 24.53±0.28% w/w. For microwave pre-treating, the tea samples were leached in distilled water at room temperature for 80 min and then exposed to microwaves at 600 W for 1 min. Maximum extraction yield from the microwave pre-treated sample by MSSE at optimum condition (90 min extraction time, 40°C extraction temperature and 20 ml/g solvent to solid ratio) was obtained 37.06±0.34% w/w. For ultrasound pre-treating, the tea samples were irradiated by ultrasonic waves at a mild condition including of 10 min irradiation time at amplitude of 70% and pulse of 0.7 s. Maximum extraction yield from the ultrasound pre-treated sample by MSSE at optimum condition (108 min extraction time, 55°C extraction temperature and 18 ml/g solvent to solid ratio) was obtained 31.47±0.38% w/w. So both of the pre-treating methods had significant effect on improving the extraction yield and softening the extraction condition in MSSE and the microwave pre-treating was the better one. The extraction yield (37.15±0.19% w/w) obtained by SOX at optimum operating condition (5h extraction time at boiling point of water) was close to those obtained by MSSE from pre-treated samples, but amounts of the total phenolic and flavonoid compounds in the SOX extract were less than those obtained by other extraction methods considered in this study that was due to prolong heating process in the soxhlet extraction.