Insight into the flavor characteristics and antioxidant activity in Xiaoqinggan black tea

Xiaoqinggan black tea is made by filling black tea into fresh citrus peel with the pulp removed, followed by sunlighting and low-temperature roasting. However, existing studies have not yet systematically analyzed the chemical basis of flavor characteristics and in vitro antioxidant activity of Xiaoqinggan black tea. In this study, a systematically analysis of Xiaoqinggan black tea, including its raw materials (black tea and citrus peel) and constituent parts (tea core and outer peel), were conducted by quantifying the functional components through high performance liquid chromatography (HPLC) and chemometrics, in combination with the electronic tongue and colorimetry assays. Additionally, the in vitro antioxidant activity of Xiaoqinggan black tea and its related samples were also evaluated through five different assays. The multivariate analysis revealed that 30 differential compounds were identified, demonstrating their key role in distinguishing the five sample groups. Notably, three polyphenols (catechin gallate, taxifolin, kaempferol), six amino acids (L-theanine, L-tyrosine, L-valine, L-methionine, L-leucine, l-lysine), and total free amino acids served as the dominant factors in unique flavor of Xiaoqinggan black tea through the correlation analysis of electronic tongue and differential compounds. Chromatic aberration analysis revealed that the tea infusion of Xiaoqinggan black tea was more vividly red and bright, and it exhibited a more intense flavor. The combined analysis of antioxidative activity and functional compounds suggested polyphenols were the main contributors to the high total antioxidant activity of Xiaoqinggan black tea. In conclusion, polyphenols and amino acids constituted the unique flavor and chromatic characteristics of Xiaoqinggan black tea, and provided an important chemical basis for its antioxidant activity. This study provides insights for improving tea processing and product quality, making it relevant to both the tea industry and scientific research.