Effects of manufacturing on the volatile composition of raw Pu-erh tea with a focus on de-enzyming and autoclaving–compressing treatments

Abstract

Volatile compounds largely contribute to the aroma of raw pu-erh tea (RPT). However, the changes of volatile composition during manufacturing are unclear. This work characterized 58 volatile compounds in the RPT samples collected from withering, de-enzyming, sun-drying, and autoclaving–compressing stages. Results show that de-enzyming and autoclaving–compressing have large effects on the volatile composition, with the total volatile contents sharply decreased by 76.68% and 35.77%, respectively. After de-enzyming, the relative content of aldehydes increased by 4.68-fold, whereas that of alkenes decreased by 2.65-fold; thus, the attractive fatty aroma must be enhanced while weakening the unpleasant grassy aroma. The volatile composition would be greatly changed by autoclaving–compressing, which is a special step for RPT production but rarely studied before. These findings revealed the changes of the volatile composition of RPT during manufacturing, especially de-enzyming and autoclaving–compressing, which are important for the formation of the aroma characteristics of RPT.