A team led by Anhui Gui and Shiwei Gao systematically compared four versions of Juhong tea, each built from a different black tea raw material. The traditional version, labeled TJH, was made from the classic one-bud-two-leaf harvest. The second, BJH, used only single buds, the most tender and prized plucking grade. The third, WJH, came from tea trees that had grown wild without human intervention for ten years. The fourth, SJH, used leaves from plants that had been shaded with nets of roughly ninety percent opacity for three weeks before harvest. All leaves came from the E’cha 1 cultivar grown in Enshi City, Hubei Province, were picked on the same day in April 2024, and were processed into black tea under identical conditions before being stuffed into Nanfeng tangerine peels and roasted. This careful standardization meant that any differences in the final product could be traced back to the tea base alone.

The researchers then deployed a battery of complementary techniques. A trained sensory panel scored appearance, aroma, taste, liquor color, and infused leaves under blinded, randomized conditions. An electronic tongue equipped with six chemical sensors measured umami, saltiness, sourness, bitterness, astringency, and sweetness in Weber-Fechner units. A spectrophotometer quantified the color of each infusion, and high-performance liquid chromatography pinned down the concentrations of free amino acids, catechins, theaflavins, caffeine, and soluble sugars. Finally, widely targeted metabolomics using ultra-high-performance liquid chromatography coupled to tandem mass spectrometry catalogued the entire nonvolatile chemical landscape of each sample, identifying a remarkable 520 metabolites across 13 chemical classes.

The sensory results revealed a clear hierarchy. The single-bud version, BJH, achieved the highest overall sensory score, driven by superior aroma and taste ratings that significantly outperformed the wild and shaded samples. The traditional TJH earned the highest infusion score at 8.98 out of 10 and displayed the most saturated red and yellow coloration, with a* and b* values of 15.37 and 83.08 respectively, compared with just 1.46 and 48.12 for the shaded tea. The electronic tongue added crucial nuance: TJH scored highest in sweetness at 8.85 and richness at 0.27, while the shaded SJH showed the lowest sweetness at 2.51 but the highest umami at 6.42. In other words, shading had shifted the taste profile from sweet-dominant to umami-rich, a transformation the researchers traced to altered photosynthesis and amino acid metabolism.

The biochemical assays explained these sensory divergences with striking precision. BJH contained the highest total free amino acids at 32.69 milligrams per gram, with theanine, the signature umami compound of tea, accounting for 86 to 89 percent of the umami amino acid fraction and peaking at 18.38 milligrams per gram in the single-bud sample. The shaded tea followed closely at 28.88 milligrams per gram, consistent with previous findings that shading suppresses amino acid catabolism and promotes nitrogen assimilation. Meanwhile, BJH also accumulated the most tea polyphenols at 44.61 milligrams per gram, whereas shading cut polyphenol content to just 20 milligrams per gram. Soluble sugars declined in a clean sequence from TJH through BJH and WJH to SJH, mirroring the electronic tongue’s sweetness readings exactly.

Some of the most interesting chemistry emerged around theaflavins, the orange-yellow pigments formed when catechins oxidize during black tea fermentation. These compounds are responsible for the coveted golden ring of a quality black tea infusion and contribute to briskness and richness. All three theaflavin monomers measured, TF3G, TF3’G, and TFDG, followed the same decreasing pattern: TJH highest, then WJH, SJH, and BJH lowest. The traditional tea’s abundance of TFDG, the most prevalent monomer in every sample, likely underpinned both its vibrant liquor color and its top electronic-tongue richness score. The wild tea, by contrast, carried the highest ratio of ester-type to nonester-type catechins at 0.72, a balance known to push flavor toward bitterness, and it also accumulated the most lignans, coumarins, and triterpenoid saponins, compounds that contribute their own bitter notes.

The metabolomic analysis, processed through principal component analysis and orthogonal partial least squares discriminant analysis, confirmed that the four teas were chemically distinct worlds. Quality control samples clustered tightly, validating the data, while the four tea groups separated clearly along the first two principal components, which together explained nearly 58 percent of the total variance. Flavonoids emerged as the largest single class of discriminating compounds, accounting for 36.7 percent of the top contributing variables, with molecules such as quercetin-3-O-rhamnopyranoside and apigenin-7-O-glucoside playing leading roles. Pairwise comparisons against the traditional tea identified 156 differential metabolites for the single-bud version, 158 for the shaded version, and 89 for the wild version, with 26 compounds dysregulated across all three comparisons. Some individual metabolites shifted dramatically: quercetol C dropped more than a thousandfold in BJH relative to TJH, while naringenin-7-O-glucoside and glutamine rose sharply in the same comparison.

Correlation analysis tied the chemistry back to perception. Umami scores correlated strongly and positively with glutamic acid, theanine, and total amino acids, while ester-type catechins such as EGCG, CG, and ECG showed negative correlations with umami. Astringency tracked with epigallocatechin, caffeine, and total flavonoids, and theaflavins correlated positively with both richness and sweetness. The single strongest relationship in the entire dataset linked soluble sugars to sweetness, with a correlation coefficient of 0.94, suggesting sugars act not only as direct sweeteners but also as modulators that mask astringency, likely by interfering with the binding of polyphenols to salivary proteins. The antioxidant assays added a functional dimension: the shaded tea showed the highest total antioxidant capacity, the traditional tea excelled at DPPH radical scavenging, and theaflavins correlated strongly with DPPH activity, pointing to their benzotropolone ring as a highly active site for hydrogen atom transfer.

The practical implications reach well beyond the teacup. For manufacturers of citrus-composite teas, the study demonstrates that raw material selection is not a minor variable but the dominant lever controlling flavor balance, color, and functional potential. A single-bud base delivers premium aroma and amino-acid-driven freshness; a traditional base provides sweetness, richness, and brilliant color; a shaded base trades sweetness for umami and antioxidant capacity; and a wild base introduces bitterness and astringency alongside a distinctive phytochemical signature. By mapping 193 discriminatory metabolites onto sensory and functional outcomes, the researchers have provided a chemical roadmap for quality control and processing optimization in a rapidly growing product category. The authors note that volatile aroma compounds and the perceptual interactions between volatiles and nonvolatiles during brewing remain to be explored, and that in vivo validation of the antioxidant benefits is still needed. But for now, the message is clear: when it comes to Juhong tea, what goes inside the tangerine peel determines almost everything you taste.

Subject of Research: How different black tea raw materials shape the taste chemistry and antioxidant properties of citrus Juhong tea

Article Title: Metabolomics and electronic tongue analysis show taste differences in Juhong tea from various black tea sources

Article References: Gui, A., Ye, F., Feng, L., Wang, S., Liu, P., Liang, J., Wang, X., Xue, J., Xiang, J., Su, F., Teng, J., Huang, J., Zheng, P., & Gao, S. (2026). Metabolomics and electronic tongue analysis show taste differences in Juhong tea from various black tea sources. Food Chemistry: X, Article 104618. https://doi.org/10.1016/j.fochx.2026.104618

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104618

Keywords: Juhong tea, citrus tea, metabolomics, electronic tongue, black tea, theaflavins, theanine, flavonoids, astringency, umami, antioxidant activity, food chemistry