Comprehensive determination of the processing level of rhizome of Polygonatum sibiricum by macroscopic, micromorphological, and microscopic characterizations

The rhizome of Polygonatum sibiricum Red. (PR, Huangjing in Chinese) has served as traditional medicine and foodstuff in China for over 2000 years. However, due to its irritating effect on the throat, Huangjing must be processed before clinical use. People have been exploring to determine the processing level of traditional Chinese medicine in an accurate tool. The evaluation of PR processing levels based on macroscopic and microscopic characteristics has not yet been performed. This study aimed to provide a convenient method to determine the level of PR processing by monitoring the changes in color and crystal inclusion. According to the Chinese Pharmacopeia (2020 edition), macroscopic, micromorphological, and microscopic observations were performed with a polarized light microscope. Color quantization based on the CIE L* a* b* color system using a CM-2300d colorimeter. Color parameters h° , L* , and ΔE* had a significant influence on the differentiation ability. The inner transverse section of PR samples gradually turned into moist black with specular luster, which was consistent with the traditional identification of "brightness like oil and color like black lacquer." The change rate of the needle crystal morphology increased with the processing level, and the change rate of the needle crystal of the fifth product was over 90%. Combined with the correlation analysis, needle-like crystals were related to color parameters and could be used as an alternative marker to discriminate PR samples from different processing levels. The results confirmed the potential applicability of macroscopic and microscopic features for the classification of PR samples with different processing levels. RESEARCH HIGHLIGHTS: Color parameters h° , L* , and ΔE* had a significant influence on the differentiation ability. Micromorphological results were consistent with the traditional identification. High correlations were found between color parameters and needle-like crystals.