Effect of the Yellowing on the Quality of Zhuyeqi Yellow Tea

The effect of the yellowing process on the quality of zhuyeqi yellow tea was studied by setting different damp leaf yellowing time (2, 4, 6 h) and different dry leaf yellowing time (12, 24, 36, 48, 60, 72 h), combined with the results of sensory evaluation and physical and chemical analysis. After being spread and fixed, the tea leaves were piled for 4~6 h under the conditions of temperature of 45 ℃ and the air humidity of 70%, rolled into strips, dried to 20% of water content, piled for 48~60 h and finally dried completely step by step. And it was found that the contents of the water extract, free amino acids and soluble sugar increased, while the contents of tea polyphenol compounds with catechins and flavonoids decreased by using this yellowing technology. The contents of ester catechins decreased. The change of simple catechins was not significant and the content of caffeine changed little. By this combination technology of yellowing process, the quality of yellow tea was the best.4 yellow teas with this technology and green tea were chosen for aroma detection analysis. A total of 110 aroma components were identified, and 57 kinds of aroma components were only identified in yellow tea. As for the 4 kinds of yellow teas, 22 kinds of common aroma components were analyzed and the composition and proportions of them were similar. They were mainly hydrocarbons, alcohols, ketones and esters compounds. The linalool oxide, geraniol, β-ionone oxide, dihydroactinidide and β-citral with pleasant aroma promoted the formation of good aroma quality of yellow tea.