ABSTRACT
Objective: To study the relationship between the quantitative color value of the powder and the known component content of rhubarb charcoal, and lay the foundation for the establishment of the rhubarb charcoal processing process control and endpoint judgment based on the color quantitative value. Methods： Rhubarb charcoal samples were prepared at different temperatures and time. Based on the empirical judgment of the rhubarb charcoal processing, the visual analyzer and UV-Vis were used to quantify the color of the pieces and powder of rhubarb charcoal under different processing conditions. At the same time, the HPLC fingerprint method was used to evaluate the dynamic changes of chemical components during the processing of rhubarb charcoal, and the quantitative value of the color of the sample during the processing of rhubarb charcoal was correlated with the characteristic components of the HPLC fingerprint using the multivariate statistical method. Results: During the processing of rhubarb charcoal, as the degree of carbonization increased, the apparent color of the sample changed from light yellowish brown to burnt black. There was a high correlation between the lightness value (L*), red-green value (a*) of the sample pieces and powder and the yellow and blue values (b*). The area of the 26 characteristic peaks had varying degrees of correlation with the chromaticity value. Among the 14 known components, five bound anthraquinones (aloe-emodin-8-O-β-D-glucoside, rhein-8-O-β-D-glucoside, chrysophanol-8-O-β-D- glucoside, emodin-8-O-β-D-glucoside, physcion-8-O-β-D-glucoside), and two sennosides (sennoside A, sennoside B) had a linear positive correlation with the chromaticity value. The content of five free anthraquinones (aloe-emodin, rhein, chrysophanol, emodin, and physcion), gallic acid and 5-hydroxymethylfurfural (5-HMF), whose contents increased first and then decreased, showed a quadratic correlation with the chromaticity value. Conclusion: The subjective judgment of rhubarb charcoal in the processing process is consistent with the quantitative color value analysis. The quantitative color value has a clear correlation with the content of 14 active chemical components. It is preliminarily inferred that the color quantitative value can be used as the quality of the rhubarb charcoal processing process control and end-point determination indicators to achieve efficient and rapid identification of the processing quality of rhubarb charcoal, which can provide new ideas for the monitoring and quality control of the rhubarb charcoal processing process.