Comparative Analysis of Flavonoids, Carotenoids, and Major Primary Compounds in Site-Specific Yellow-Leaf Tea and Their Dynamic Alterations During Processing

Yellow-leaf tea cultivar ‘Huangjinya’ is valued for distinctive appearance and umami flavor, yet the mechanisms underlying pigment accumulation and flavor formation responding to cultivation and processing remain unclear. Targeted metabolomic quantified 16 carotenoids and 18 flavonoids, revealing significantly higher concentrations in high-altitude site fresh leaves (551.88 ± 7.09 μg·g−1 and 213.91 ± 3.78 mg·g−1, respectively), approximately 2.8-fold and 1.2-fold higher than in low-altitude site samples. These observed regional differences likely reflect environmental differences between the high- and low-altitude cultivation sites. Flavonoids remained relatively stable during green tea (GT) processing but declined markedly during black tea (BT) production. Carotenoids decreased by 27.91% during green tea (GT) processing but increased by 43.64% in black tea (BT) when using low-altitude site fresh leaves; in contrast, high-altitude site leaves showed a 4.66% increase in GT and a sharp 65% decrease in BT. Thirty-eight primary metabolites showed significant changes responding to altitudes and processing, especially amino acids and oligosaccharides. These findings clarify how altitude and processing affect flavor-related metabolism in ‘Huangjinya’, offering a chemical foundation for improving tea quality.