Changes on Free Amino Acids in Fresh Tea Leaves during Withering

Withering in tea processing significantly affects the flavor of white, black and oolong teas. The spring shoots (i.e., a bud, 2^nd and 3^rd leaves, or 2^nd to 4^th leaves on a banjhi bud) harvested from 10 tea cultivars were used in the experimentation. The withering chamber was controlled at 20～22℃ and 35%～45% RH. The changes on free amino acid contents in the tea leaves at various withering stages were monitored. The results showed that the leaf samples could be classified into two groups based on the maturity of the shoots. All teas prepared could be differentiated by their weight losses (i.e., 0%, 15%, 30%, 45% and 60%) at different stages of withering. As the leaf weight decreased, changes were apparent on the typical free amino acids found in teas, including Thea, Asp, Glu, Arg, Thr, and Ser. Especially after the leaves lost 30% of their original fresh weight, the tea samples showed a significant spreading on the 2^nd order dimension distribution, indicating diversified amino acid compositions among different varieties of the teas during withering. There appeared a trend in increasing the contents of Asp, Glu and Ser, and declining in that of Thea as the withering progressed.