Seasonal Changes in Activities of Enzymes Responsible for the Formation of C<sub>6</sub>-aldehydes and C<sub>6</sub>-alcohols in Tea Leaves, and the Effects of Environmental Temperatures on the Enzyme Activities

Abstract

When tea leaves were homogenized and incubated, the volatile C6-compounds hexanal, cis-3-hexenal, cis-3-hexenol and trans-2-hexenal were formed much more by summer leaves than by winter leaves of tea plants (Camellia sinensis). The enzymes lipolytic acyl hydrolase (LAH), lipoxygenase, fatty acid hydroperoxide lyase (HPO lyase) and alcohol dehydrogenase (ADH) and an isomerization factor were responsible for the sequential reactions of C6-compound formation from linoleic and linolenic acids in tea leaf lipids, and there were seasonal changes in their activities. The tea leaf enzymes were of 3 types: LAH and lipoxygenase, which had high activities in summer leaves and low activities in winter leaves; ADH, which had low activity in summer leaves and high activity in winter ones; and HPO lyase and the isomerization factor, which did not seem to have any effect on the rate of C6-compound formation throughout the year. Changes in enzyme activities were induced by shifts in the environmental air temperature rather than by the age of the leaves. The combined activities of these enzymes determined the amounts and compositions of the volatile C6-compounds formed, which are the factors that control the quality of the raw leaves processed for green tea.