(−)-EC, (−)-EGC, (−)-EC gallate (ECG), and (−)-EGC gallate (EGCG) [high performance liquid chromatography (HPLC) ≥98%] were purchased from QualiFlex Co. (Taipei, Taiwan). Caffeine (≥99%) was obtained from Merck KGaA (Darmstadt, Germany). Acetic acid (99.7%) was purchased from J. T Baker (Mallinckrodt Baker, Inc., Phillipsburg, NJ, USA). Acetonitrile (HPLC grade) was obtained from Thermo Fisher Scientific (Waltham, MA, USA). Water was purified by a Millipore clear water purification system (Millipore Direct-Q, Millipore, Bedford, MA, USA).
All of the fresh tea leaves and oolong tea granules were obtained from the same tea plant cultivar, Camellia sinensis L., Chin-Shin oolong, grown at different altitudes in the same mountain area of Center Taiwan in November 2012 and December 2012. Both fresh tea leaves (with young green shoots used for the preparation of oolong tea) and their consequent oolong tea granules were obtained from three tea farms at altitudes of 200 m, 800 m, and 1300 m, respectively. In addition, seven more fresh leaves from altitudes of 220 m, 400 m, 1000 m, 1200 m, 1350 m, 1550 m, and 1600 m, as well as seven more oolong tea granules from altitudes of 170 m, 850 m, 900 m, 950 m, 1100 m, 1500 m, and 1600 m were collected for the following analysis.
All of the fresh tea leaves and oolong tea granules were obtained from the same tea plant cultivar, Camellia sinensis L., Chin-Shin oolong, grown at different altitudes in the same mountain area of Center Taiwan in November 2012 and December 2012. Both fresh tea leaves (with young green shoots used for the preparation of oolong tea) and their consequent oolong tea granules were obtained from three tea farms at altitudes of 200 m, 800 m, and 1300 m, respectively. In addition, seven more fresh leaves from altitudes of 220 m, 400 m, 1000 m, 1200 m, 1350 m, 1550 m, and 1600 m, as well as seven more oolong tea granules from altitudes of 170 m, 850 m, 900 m, 950 m, 1100 m, 1500 m, and 1600 m were collected for the following analysis.