## 3 Results and Discussion
### Analysis of the Effects of YLDI on the Volatile Compounds of Green Tea Using GC-MS/MS
#### 3.3.5 Analysis of the Metabolic Pathways of Key Volatile Compounds  
By the metabolic pathways involved, the 21 key volatile components discussed above were subcategorized into four classes, as illustrated in Figure S4. According to [PERSON] et al. [23], these comprised three carotenoid-derived volatiles (CDVs), nine fatty acid-derived volatiles (FADVs), six amino acid-derived volatiles (AADVs), and three glycosiderived volatiles (GDVs). FADVs are primarily derived from the oxidative degradation of unsaturated fatty acids via the lipoxygenase pathway (Figure 5). The common precursor substances in tea mainly include \(\alpha\)-inolenic acid, palmitoleic acid, and linoleic acid [32]. As a crucial odorant in green tea [34], 1-octen-3-ol attained its maximum of 4.45 \(\mu\)g/L under 1000 Lux, then declined as the light intensity increased, mirroring the findings by [PERSON] et al. [35]. As shown in Figure 6A, the trend for (\(E\))-2-nonneal was opposite, with the lowest concentration (4.15 \(\mu\)g/L) under 1000 Lux. As previously highlighted, (\(E\), \(E\))-2,4-nonaldienal and (\(E\), \(E\))-2,4-decadienal demonstrated a high correlation, both exhibiting a trend of initial decrease followed by an increase under different light intensities. _Cis_-jasmone, decanal, heptanal, and (\(E\), \(Z\))-2,6-nonaldienal attained their highest concentrations at 1000 Lux, whereas octanol peaked at 4000 Lux. Geraniol and linalool serve as typical GDVs, synthesized via the intermediary geranyl pyrophosphate (geranyl-PP). These enzymes, namely geraniol synthase and linalool synthase, respectively, catalyze this liberation process (Figure 5). As important aroma compounds in black tea, linalool and geraniol impart sweet, floral, fruity, rose-like, and waxy notes [23]. As shown in Figure 6B, linalool and geraniol reached the lowest concentrations under 2000 Lux (52.81 \(\mu\)g/L) and 4000 Lux (99.13 \(\mu\)g/L), respectively, and attained their highest concentrations both under 6000 Lux (91.76 \(\mu\)g/L and 179.25 \(\mu\)g/L, respectively). Citral attained its highest concentration under 1000 Lux (6.02 \(\mu\)g/L), noticeably higher than in other light intensities [36; 37]. This divergent pattern may indicate variations in the biosynthetic regulation of these compounds. Specifically, citral is synthesized through the oxidation of geraniol and may be subject to downregulation or degradation in conditions of elevated light intensity. Conversely, linalool and geraniol appear to directly benefit from light-induced metabolic flux within the methylerythintol phosphate (MEP) pathway. Light can induce the up-regulation of the expression of MEP pathway genes, and this evidence conclusively corroborates the light-intensity-dependent metabolic channeling mechanism governing linalool and geraniol biosynthesis [35]. The AADVs, such as 3-methyl-butanal, phenylacetaldehyde, and 2-methyl-propanal, are typical Strecker aldehydes (Figure 5). They are generated via the Strecker degradation pathway, utilizing their respective amino acids of leucine, phenylalanine, and valine as precursors [32]. These AADVs exhibited distinct responses to light intensity. 2-Methyl-propanal attained its maximum (10.96 \(\upmu\)g/L) under 1000 Lux treatment; Phenymacetaldehyde exhibited a V-shaped trend, with the highest concentration (91.03 \(\upmu\)g/L) under 6000 Lux treatment; 3-Methyl-butanal peaked under 1000 Lux treatment, with a concentration of 27.16 \(\upmu\)g/L (Figure 6C). Indole, another AADV, is generated from tryptophan via the action of tryptophan indole-lyase. It was reported as a pivotal floral aroma constituent in jasmine tea [32; 38]. Guaicaol was reported to be derived from phenylalanine [39]. Both indole and guaicaol exhibited upward trends with the increasing of light intensity, attaining peak concentrations at 4000 Lux (220.94 \(\upmu\)g/L) and 6000 Lux (6.44 \(\upmu\)g/L), respectively. It is speculated that high intensity of yellow light promotes the metabolism of phenylalanine-guaiacol and tryptophan-indole [7].