Changes on Catechin and Alkaloid Contents in Fresh Tea Leaves During Withering

Under controlled indoor conditions at 20-22℃and 35%-45% RH,withering of the spring tea shoots,i.e.,2or 3leaves with a bud(A)and 2to 4leaves with a banjhi bud(B),harvested from 10 tea cultivars,including Rougui and Shuixian,was conducted to study the compositional changes in the leaves.Samples were collected at water loss of the leaves at 0,15%,30%,45% and 60% to determine the catechin and alkaloid contents using HPLC.The results showed that the highest contents of catechin monomers and total catechins occurred when water loss of the leaves was in the range of 30% to 45%,indicating transformation of catechinsduring early stage of withering.As the withering progressed,EGCG,EC,ECG and total catechins of the samples began to fall,and EGC and TB reduced gradually,while CAF and alkaloids increased.The scope of the changes were more prominent in Group A than B.The principal component analysis(PCA)and the cluster analysis rendered a similar classification in dividing the 110 samples into the two types,A and B,which were grouped based on the tenderness of the tea shoots.The PCA results suggested that tea catechins and alkaloids rose and fell due to the oxidization and degradation of catechins by the polyphenol oxidase during the time period.Apparently,withering affected the contents of catechins and alkaloids in the leaves.Therefore,it was conceivable that proper control on moisture loss of the leaves could improve the flavoring and active components of the resultant tea.