## 3 Results and Discussion
### Quantitative Differences between FKBT and 1Y-KBT

Table 3: (**A**) Concentrations of key aroma volatiles in FKBT and 1Y-KBT infusions. (**B**) OAVs of key aroma volatiles in FKBT and 1Y-KBT infusions. Except for dimethyl sulfide, the concentrations of the sulfide compounds (dimethyl disulfide, methional, and dimethyl trisulfide) were also higher in the FKBT infusion than in the 1Y-KBT infusion; the ratios were 7.9, 4.1, and 2.4, respectively. In an earlier analysis of KBT after 1 to 20 years of storage, dimethyl disulfide was detected in only 1Y-KBT and neither methional nor dimethyl trisulfide were detected in any stored samples. Methional is a Strecker aldehyde of methionine and both dimethyl disulfide and dimethyl trisulfide are further oxidation products of methional [20]. Methional's aroma has been described as cooked potato in several reports [21; 22] but we linked it with the characteristic sweet aroma of high-grade FKBT in our GC-O-MS experiment. The concentration of methional in the FKBT infusion was 4.2 \(\upmu\)g/L and those of both methyl disulfide and dimethyl trisulfide were <1.0 \(\upmu\)g/L. The OAVs of methional and dimethyl trisulfide were >1 in both the FKBT and 1Y-KBT infusions, indicating that these compounds contributed to the aromas. Among the six volatiles with a floral aroma, benzeneacetaldehyde was slightly more abundant in the FKBT infusion and the concentrations of linalool, geraniol, and (Z)-methyl epijasmonate were 2.5, 2.2, and 5.1 times higher in the FKBT infusion; except for that of (Z)-methyl epijasmonate, the concentrations of the compounds were all >100 \(\upmu\)g/L. The concentration of phenylethyl alcohol was slightly lower in the FKBT infusion than in the 1Y-KBT infusion but both concentrations were >400 \(\upmu\)g/L. These results generally support our previous conclusions that storage has a negative effect on floral compounds, especially linalool, geraniol, and (Z)-methyl epijasmonate. Linalool, geraniol, and benzeneacetaldehyde contributed greatly to the floral aroma of the FKBT infusion, especially linalool, which had an OAV of 257. Although it was considerably reduced during storage, the OAV of linalool remained at 102 in the 1Y-KBT infusion. (Z)-methyl epijasmonate, a key aroma volatile in tea, contributed only slightly to the aroma of the FKBT infusion, with an OAV of 1. The acidic aroma volatiles exhibited similar trends. The concentrations of benzeneacetic acid and benzoic acid in the 1Y-KBT infusion were 4.4 and 3.1 times higher, respectively, than in the FKBT infusion. Hexanal, the only green/grassy aroma volatile with an FD value \(\geq\)16, is derived from lipid oxidation during tea processing [20]. The concentration of this compound in the FKBT infusion (165 \(\upmu\)g/L) was 4.2-folds higher than in the 1Y-KBT infusion. The OAVs of hexanal in both KBT infusions were higher than 1. The concentrations of all eight sweet aroma volatiles in both KBT infusions were <30 \(\upmu\)g/L. Methional, coumarin, and \(\updelta\)-decalactone were more abundant in the FKBT infusion and the other five sweet volatiles were more abundant in the 1Y-KBT infusion. The concentrations of \(\updelta\)-octalactone, vanillin, and herniarin in the FKBT infusion were all 0.9 times lower than those in the 1Y-KBT infusion and the concentrations of \(\upbeta\)-damascenone and raspberry ketone were 0.6 and 0.3 times lower than those in the 1Y-KBT infusion. Among the sweet aroma volatiles, only \(\upbeta\)-damascenone, methional, and coumarin had OAVs > 1. Though low concentrations of \(\upbeta\)-damascenone were present in the KBT infusions (both <1 \(\upmu\)g/L), its OAVs were still much higher (61 and 108 in FKBT and 1Y-KBT, respectively) than those of methional and coumarin because of its extremely low threshold. \(\upbeta\)-Damascenone receives tremendous attention because it can easily achieve high FD in GC-O experiments and has a high OAV due to its extremely low threshold. \(\upbeta\)-damascenone exists in various teas, fruits, coffees, honeys, wines, and other foods and drinks [23].