While key aroma and taste compounds of Keemun Congou black teas (KCBT) form during aeration and thermal stages, it is still unknown whether these processing stages also produce non-volatile color-contributing metabolites. Through integrating metabolomics with correlation and ridge regression analyses, 190 metabolites were identified as marker compounds that reclassified 15 KCBT samples collected from five processing stages into four groups. Meanwhile, the results of quantification and heatmap analysis showed that the concentrations of theaflavins and theasinensins significantly increased, as catechin decreased, after rolling, while flavonoid aglycones and polyunsaturated fatty acids increased throughout drying. Regression analysis between marker compound levels and total color difference values (∆E) revealed that the major color contributors were 3,5-dicaffeoylquinic acid, glucosyl-dehydrodigallic acid, theacitrin A, kaempferol-O-robinobioside, and (−)-epigallocatechin, with regression coefficients (absolute value) exceeding 4 × 10−2. Overall, the present study confirmed that rolling and drying were the two vital stages responsible for the color formation of KCBT.

中文翻译：

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开发的代谢组学方法揭示了Keemun Congou红茶加工过程中的非挥发性色素贡献代谢物


虽然 Keemun Congou 红茶 （KCBT） 的关键香气和味道化合物是在通气和加热阶段形成的，但这些加工阶段是否也产生非挥发性色素贡献代谢物仍是未知数。通过将代谢组学与相关性和岭回归分析相结合，确定了 190 种代谢物作为标记化合物，将从 5 个加工阶段收集的 15 个 KCBT 样品重新分为四组。同时，定量和热图分析结果表明，擀制后茶黄素和茶素的浓度显著增加，儿茶素含量降低，而黄酮苷配基和多不饱和脂肪酸含量在整个干燥过程中增加。标记化合物水平和总色差值 （∆E） 之间的回归分析显示，主要的颜色贡献者是 3,5-二咖啡酰奎宁酸、葡萄糖基脱氢二甲酸、茶精 A、山奈酚-O-刺槐生物苷和 （-）-表没食子儿茶素，回归系数 （绝对值） 超过 4 × 10−2。总体而言，本研究证实了轧制和干燥是导致 KCBT 颜色形成的两个重要阶段。