Shaking the tea leaves is the key manipulation to making oolong tea. It contributes to the formation of flavor and fragrance in oolong tea. The dynamic variations of catechins and volatile organic compounds (VOCs) during the shaking process were investigated. The results showed that the contents of epicatechin, epigallocatechin, epicatechin gallate (ECG), and epigallocatechin gallate (EGCG) first decreased after the shaking and then increased to the initial value before the next shaking. Geraniol, linalool and its oxides, and phenylethyl alcohol showed similar variations. The contents of trans-β-ocimene, 1H-indole, and 3-hexenyl hexanoate increased after the second or third shaking (the late fermentation stage). However, the contents of aldehydes showed an opposite trend to other VOCs. The abundance of phenylethyl alcohol was positively related to the content of ECG and EGCG ​during fermentation, whereas the abundance of cis-3-hexenal was negatively related to the content of ECG. The correlations between catechin and VOCs indicated that shaking affected the chemical transformation of the compounds in oolong tea.

The manufacture of semi-fermented oolong tea is a skilled task requiring “sniffing indices” during processing. An experienced “sniffer” uses the appearance of grassy and floral fragrances to monitor the progress of fermentation. In the present work, semi-fermented oolong tea was sampled at 13 Stages of processing. At each stage, volatile compounds were collected by solid-phase micro-extraction and investigated by GC-MS analysis. It was found that C₆ aldehydes remained at constant levels throughout fermentation. Those volatiles responsible for the fragrance of oolong tea increased up to the end of fermentation. Trans- β-ocimene, α-farnesene, and 3-hexenyl hexanoate reached peak levels before heat fixation (“panning”). The fruity volatiles were C₁₀ or C₁₂ esters. Significant variations in trans- β-ocimene, linalool (and its oxides), 1H-indole, and α-farnesene accompanied the appearance of the floral fragrance. There was a 14.7% decrease in total catechins between the fresh tea shoots (Stage 1) and the end of fermentation (Stage 12). Epi-catechin, epi-gallocatechin, and epi-gallocatechin gallate decreased by 8%, 42%, and 5%, respectively, whereas epi-catechin gallate increased by 13% at the end of fermentation (Stage 12). Total catechin galate ester levels were raised significantly at the floral fragrance Stages (Stages 3, 4, 6, 8, 10, and 12).

The volatile components of fresh leaves from 15 citrus species were investigated by headspace SPME with a GC-MS analysis. Three indigenous Taiwan citrus species, Citrus taiwanica, C. tachibana and C. depressa, were the major subjects. Eighty volatile organic compounds were detected as indicators of the genetic relationship. Linalool was the most abundant compound, and citronellal, geranial, neral, limonene and trans-beta-ocimene were the major volatile compounds in fresh leaves. Linalool (56.37%) and myrcene (7.21%) were predominant in C. tawanica. An aldehyde-rich profile with citronellal (24.54%) contributed most to the aroma of leaves in C. tachibana, while Citrus depressa exhibited a high linalool/citronellal composition (23.56%/12.51%). The qualitative and quantitative patterns of the volatiles revealed that C. taiwanica was linked with sour orange, and either C. tachibana or C. depressa belonged to the mandarin group with C. tankan. Dendrograms also showed that the volatile patterns were related to the genetic classification.

Avocados may suffer from short-term waterlogging stress when exposed to high temperatures and heavy rainfall during the summer in Taiwan. We compared the waterlogging responses of own-rooted and grafted seedlings of two Taiwan cultivars, ‘Black-Beauty’ and ‘Hung-Hsin-Yuan’, by stomatal conductance (gs) and chlorophyll fluorescence parameters. Four-day waterlogging and four-day post-waterlogging recovery periods were investigated. Both gs and Fv/Fm of own-rooted seedlings of two cultivars were significant reductions in response to short-term waterlogging. The grafted seedlings on the same cultivar rootstock were evaluated by gs and Fv/Fm during the growth and the growth cessation periods, respectively. The combined responses of gs and Fv/Fm under short-term waterlogging showed that ‘Black-Beauty’ was sensitive to stress because of decreased gs after waterlogging or decreased Fv/Fm after the two-day recovery period. ‘Hung-Hsin-Yuan’ showed more tolerance to waterlogging stress, especially during the growth cessation. This indicates that the vegetative dormancy may affect the evaluation of the stress response of avocados. Our results revealed that gs and Fv/Fm can be effective indicators in the four-day waterlogging of avocado, and the growth status of avocado seedlings should be considered during stress-tolerant variety selection.