Changes on Major Quality Indices in Tea Leaves during Withering

Fresh spring shoots (two or three leaves and a bud) harvested from 10 tea cultivars were used in this experimentation conducted at 20～22℃and 35%～45% RH. Changes on the major chemical components in the tea leaves as indices for quality were monitored at various withering stages. The results showed that, with increasing weight loss on the fresh tea leaves, there appeared to be a continual increase on the contents of water extracts, caffeine, free amino acids, and water soluble sugars, while polyphenols increased initially and followed by a decline in the leaves. These changes were not parallel. For instance, when the water loss was less than 15%, no significant alternations were observed in regard to the contents of ～45% during withering, the water soluble sugars and caffeine, as well as the water extracts, reached their maximums. As the weight loss increased to 60%, only the contents of free amino acids continued to increase. At end of the withering process, the most significant changes were found on the contents of free amino acids, water soluble sugars, and caffeine, with increases of 24.6%, 13.8%, and 11.9%, respectively. The correlation analysis showed that (1) the weight loss of tea leaves during withering significantly affected the contents of free amino acids, water soluble sugars, water extracts, and caffeine, with correlation coefficients of 0.413, 0.386, 0.692, and 0.479, respectively; (2) the change on free amino acids content was particularly significant; and, (3) no significant effect was observed on the content of polyphenols.these components (on a dry matter basis). However, as the weight loss approached 30%