Effect of Different Fixing Methods on the Quality Formation of Flat-shaped Green Bud Tea

To investigate the effects of different fixation methods on the flavour of flat-shaped green bud tea, high-performance liquid chromatography (HPLC), headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC/MS) were conducted to analyse the biochemical components and aroma changes during processing. The results showed that microwave supplementary fixing improved the quality of the soup color, aroma, and taste of the flat-shaped green bud tea. It benefited the transformation and generation of tea polyphenols, free amino acids and soluble sugars in the processed tea, as well as the later generation of catechin (C), gallocatechin (GC) and epicatechin (EC) during the processing. A total of 972 and 966 volatile metabolites were detected in the control group (CK) and the microwave supplementary fixing group (WB) respectively. In the two fixation treated groups, significant differences in volatile metabolites were detected among the fresh leaves, fixation leaves and processed teas. Microwave supplementary fixing enriched the types of tea aroma, with more differential metabolites between fixation leaves and processed tea identified than those between fixation leaves and fresh leaves. Analysis of the relative odor activity value (rOAV) of the differential metabolites showed 6 and 9 differential metabolites with rOAV>1 from the CK group and the WB group respectively, which were speculated to be the key aroma substances responsible for the aroma changes in each treatment. Among them, 1-decanol, (E)-3,7-dimethyl-2,6-octadialdehyde, and citral mainly contributed to the aroma and flavor similar to orange, while p-cymene, methyl anthranilate, and o-cymene exhibited a mild and pleasant aromatic, orange, and floral flavor. They were the main substances responsible for the differences in the aroma quality of the processed teas by different fixation methods. This study provided a theoretical basis for the generation of the different characteristics of flat-shaped green bud tea and the optimization of their processing technology in the Sichuan-Chongqing region.