Journal of Tea Science Research, 2024, Vol.14, No.5, 249-261 http://hortherbpublisher.com/index.php/jtsr 255 6.2 Fermentation practices in green and oolong tea Fermentation practices also play a significant role in the production of green and oolong teas. The application of methyl jasmonate (MeJA) has been shown to enhance the aroma quality of green, oolong, and black teas. MeJA treatment modulates the aroma profiles by increasing the levels of specific VOCs such as benzyl alcohol, benzaldehyde, and 2-phenylethyl alcohol, which contribute to a more pleasant aroma (Shi et al., 2019) (Figure 3). In the case of oolong tea, optimizing processing techniques to balance high retention of catechins and sensory quality are essential. A study demonstrated that specific processing steps, including red light withering, leaf rotating, drum roasting, low-temperature rolling, and95 microwave drying, significantly increased the retention of catechins, contributing to the mellow and brisk tastes of oolong tea (Lu et al., 2023). Furthermore, the fermentation of autumn green tea with Eurotium cristatum has been shown to improve its taste quality by reducing astringency and enhancing the umami intensity, primarily through the oxidation of catechins (Xiao et al., 2021). Figure 3 Key volatile compounds in tea products produced from MeJA-treated fresh tea leaves (Adopted from Shi et al., 2019) Image caption: (A) Differentially abundant VOCs in three kinds of tea products. Radar maps of differentially abundant VOCs in (B) green tea (GT), (C) oolong tea (OT), and (D) black tea (BT) prepared from MeJA-treated fresh tea leaves (FL). All tea products prepared from MeJA-treated fresh tea leaves after 0, 12, 24, 48, and 168 h. Sampling times of oolong tea and black tea were identical. Color scale in (A) represents fold changes, in general “white” means “no change”, “red” means “increase”, and “green” means “decrease” (Adapted from Shi et al., 2019) The research of Shi et al. (2019) presented an analysis of key VOCs in green, oolong, and black tea products derived from methyl jasmonate (MeJA)-treated fresh tea leav`es. The heat map (A) highlighted the differential abundance of VOCs, showing varied responses to MeJA treatment over time. Compounds such as cis-3-hexenol,
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