Flush-dependent formation of industrial black tea liquor color: Integrating oxidation pigments with physicochemical quality indices through predictive modeling.

Traditional assessment of industrial black tea liquor color has predominantly focused on oxidation pigments, often overlooking the influence of routine physicochemical quality indices. This study fills this gap by, for the first time, jointly quantifying the relative contributions of oxidation-derived pigments (TF, TR), caffeine, and routine physicochemical quality indices (water extract, total ash, acid-insoluble ash (AIA), and moisture) within a unified, flush-resolved analytical framework. Spearman analyses revealed strong negative associations between color intensity and moisture, total ash, and acid-insoluble ash, and a strong positive association with water extract, while brightness was positively linked to TF and the TF/TR. Regression models identified TF and AIA as the principal predictors of liquor color, AIA and total ash as key determinants of brightness, and water extract as the dominant driver of color intensity. Random forest analysis supported the multivariate structure of color formation and confirmed the relative importance of both pigment and non-pigment quality indices. These findings demonstrate that black tea liquor color is governed by integrated compositional interactions rather than pigment concentration alone. This integration establishes a compositional basis for reinterpreting industrial black tea liquor color beyond pigment-centric evaluation. This study also provides a flush-aware framework for interpreting the formation mechanism of industrial black tea liquor color and advances objective, QC-oriented modeling in industrial contexts.