烏龍茶與老茶的化學成分分析研究

Abstract

烏龍茶是經過部分發酵所製成的茶葉，是一種味道與色澤界於綠茶與紅茶之間的茶種。不同的烏龍茶湯會因為其製成的差異而有不同，尤其是酚類化合物可以利用高效液相層析(High-performance liquid chromatography) 與紫外偵測器或電噴灑離子化串聯式質譜(electrospray ionization tandem mass spectrometry)進行分析茶所改變的組成成分。因此分析烏龍茶組成成分，共分析出2個生物鹼(alkaloids)，11個黃烷醇(flavanols)，8個有機酸和酯類， 11個原花青素二聚體(proanthocyanidin dimmers)，3個茶黃素(theaflavins)和22個總黃酮類(flavonoid glycosides)，其中包含6個醯化黃酮醇配醣體(acylated flavonol glycosides)。利用光譜方法分析其中兩個主要的醯化黃酮醇配醣體的結構，分別為quercetin 3-O-[2G-(E)-coumaroyl-3G-O-β -D-glucosyl-3R-O-β-D-glucosylrutinoside] 和 kaempferol 3-O-[2G-(E)-coumaroyl-3G-O-β-D-glucosyl-3R-O-β-D- glucosylrutinoside]。烏龍老茶為上等茶，經長期的保存並且伴隨著周期性的烘培達到精緻化所製備而成，經驗上被認為對於人體健康有益。分析三種老茶與一種新製備的烏龍茶的茶湯成分，比較兩者發現，在老茶中其EGCG 〔(-)-epigallocatechin gallate〕會顯著降低而沒食子酸卻大量增加，並且一些特殊的黃酮類( myricetin、quercetin和kaempferol )會出現，推測可能是原本烏龍茶中的總黃酮類裂解所產生。

Oolong tea manufactured via a semifermentation process possesses a taste and color somewhere between green and black teas. Alteration of constituents, particularly phenolic compounds, in the infusion of oolong tea resulted from its manufacture, was analyzed by high-performance liquid chromatography coupled to ultraviolet absorbance or electrospray ionization tandem mass spectrometry. The identified contained 2 alkaloids, 11 flavan-3-ols, 8 organic acids and esters, 11 proanthocyanidin dimers, 3 theaflavins, and 22 flavonoid glycosides, including 6 novel acylated flavonol glycosides. The structures of two major acylated flavonol tetraglycosides were elucidated by spectroscopic methods as quercetin 3-O-[2G-(E)-coumaroyl-3G-O-β-D-glucosyl-3R-O-β-D-glucosylrutinoside] and kaempferol 3-O-[2G-(E)-coumaroyl-3G-O-β-D-glucosyl-3R-O-β -D- glucosylrutinoside]. Old oolong tea, tasting superior and empirically considered beneficial for human health, is prepared by long-term storage accompanied with periodic drying for refinement. Analyzing infusions of three old and one newly prepared oolong teas showed that significant lower (-)-epigallocatechin gallate (EGCG) but higher gallic acid contents were detected and unique occurrence of flavonols (myricetin, quercetin,and kaempferol) putatively decomposed from flavonol glycosides was observed in the old teas compared with the new one.