A Study On Annual Variation Characteristics Of The Major Compounds In Tea Leaves

Tea plants (Camellia sinensis (L.) O.Kuntze) originated in southwest China, are a perennial crops whose leaves and leaf buds are used to process the popular beverage tea. It is known that there are 700 kinds of compounds in tea leaves, in which the main components are characteristic compounds such as polyphenols, alkaloids, theanine, pigments, aromatic substances. Those determine somehow the final tea quality. In order to well understand the annual variation of three characteristic material in tea as catechins, caffeine and free amino acids including theanine, three national-level tea varieties Shuchazao, Longjing 43 and Nongkangzao, growing at the experimental tea garden of Anhui Agricultural University at Hefei city, were selected and the high-performance liquid chromatography (HPLC) was applied to quantify the metabolite content at picked tea leaves. The samples were hand-plucked from buds and leaves of tea shoots according to their leaf order every month from December 2010 to November 2012 for a total of 24 months, which were further underwent microwave fixation to dry and then used for qualification of catechins, caffeine and free amino acids. Their annual variations were analyzed statistically and the similarities and difference between bud and leaf order, as well as 3 different varieties were compared. The main results are as follows.First, the moisture contents of tea leaves samples from three varieties ranged from 52.3% to 76.9% with the average of 64.6%. It is shown that in the annual growth and development cycle, the trends of moisture content chang with climate. Tea leaf moisture increased to the highest value in spring sprouting period while those in the summer and autumn lowered slowly with fluctuation and finally to the lowest level at the dormancy period in winter. The leaf moisture content in tea leaves at all three varieties tended to decreas with leaf maturity increase.Second, the catechins'content in tea leaves from three varieties were between 7.50mg/g-146.98mg/g with average of 69.78mg/g. In different months, the total amount of catechin changed obviously. It founded that those at the beginning of winter maintained at low levels and increased persistently in late winter; Before the sprouting stage of new shoots in spring season, their amount declined sharply to a lower level and at the late sprouting stage they climbed to a higher level; In summer, they had a growth peak in the middle time, while those in autumn kept at a high level. The amount of total catechins of tea leaves in spring, summer and autumn were 52.67mg/g?117.02mg/g, Comparably, in all of three tea varieties, the catechins in spring were lower than those in summer and autumn, while those in younger leaves were higher than those in older leaves.The average amount of total catechins in 2011 and 2012 were compared as Shuchazao (56.26mg/g?90.54mg/g)>Longjing43 (54.22mg/g.?88.18mg/g)>Nongkangzao (52.98mg/g?78.44mg/g). Among total catechins, an important catechin EGCG accounted for 30% of the total amount has showed the similar variation tendency as the total catechins.Third, the caffeine content changed obviously in different seasons. In the wintering period, its content kept at a low level of around 5mg/g. In the sprouting period, it rapidly increased to 20mg/g?43 mg/g and dropped to 17mg/g?19mg/g between spring and summer. The order of caffeine content in different season were as spring>autumn>summer, while in different leaves, the more tender of the leaves has a more higher content. The average caffeine amount in 2011 and 2012 were in Longjing 43 (12.71mg/g?15.60mg/g)> Nongkangzao (12.06mg/g,12.82mg/g)> Shuchazao (11.90mg/g,12.37mg/g).Fourth, the free amino acids and theanine were at a low level in the wintering period and increase rapidly to the highest level in the spring sprouting period and then decreased gradually through autumn to winter. Theanine and 18 kinds of free amino acids in tea leaves from different seasons had a order as spring> autumn> summer. Moreover, those in spring were much higher than those in summer and autumn. In different leaf positions, they had a higher content in tender leaves. In the 3 different varieties in 2011 and 2012, their content differed as Nongkangzao (11.54 mg/g, 4.29mg/g)> Longjing 43 (9.10 mg/g,3.62 mg/g)> Shuchazao (7.92mg/g,2.74 mg/g). The ratio of theanine amount to the total of 18 kinds of free amino acids were at 1.7%?46.8%, while the ratio in the wintering period was at a low level at about 10% and in the sprouting period, it increased significantly to about 40% and then declined significantly, but re-increased in September to a high level.In conclusion, the characteristic secondary material catechin, caffeine and theanine in all 3 varieties have shown a similar growth variation. In the spring sprouting season, the content of caffeine and theanine are highest while catechins are relative high. With the seasonal growth, caffeine and theanine decrease gradually while catechins increase in summer and autumn. In the different leaf position, the content of those material as well as moisture content decrease with the leaves maturity.