Abstract:In order to investigate the effect of vacuum freeze-drying on the aroma characteristics and volatile matter of instant tea powder, headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (GC-MS) was used to analyze the volatile components in concentrated Oolong tea extract and its tea powder prepared by vacuum freeze-drying. GC-MS analysis showed that 74 volatile components were identified, with the main volatile compounds in concentrated Oolong tea extract being indole, 2-ethyl-furan, and para-cymene, and the main volatile compounds in the vacuum freeze-dried Oolong tea powder being indole, hexanal, and linalool. Cluster analysis showed that nine volatile compounds, including 2-ethyl-furan, disappeared, while 23 new volatile compounds, including hexanal, were generated after vacuum freeze-drying. Additionally, the concentrations of 2-heptanone and (E)-β-ocimene decreased during vacuum freeze-drying, while the concentrations of (E)-nerolidol and six other compounds increased simultaneously. The result of odor-activity values showed that (E)-2-nonenal and (E,E)-2,4-decadienal were the main odor-active contributors of the concentrated tea extract. As for the freeze-dried tea powder, the main odor-active compounds were 1-octen-3-ol, linalool, and n-hexanal. These results indicated the significant effects of vacuum freeze-drying on the volatile components and aroma characteristics of concentrated Oolong tea extract and provided a theoretical reference for the production of instant tea powder.
