Effect of heat processing on the quality and alkaloid contents of Coptis Rhizome

ABSTRACT Aim The outer color of the Chinese herbal medicine Oren (Coptis Rhizome) in the market has lately been darker than usual. A survey in China revealed that the preparation process was performed in conditions of excessive heat, and as a result there was concern about both the medicine's ingredients, as well as properties such as color and taste. Therefore, in the current study, we examined the influence of excess heat during processing on the ingredients and properties of Coptis Rhizome. Methods We obtained six samples of heat‐processed chopped Oren pieces from a market in Japan, sorted the pieces into three groups according to the color, and measured the alkaloid content in each color group. In addition, the effect of heating on the alkaloid content was examined by directly heating Oren. Results In each sample, 7–31% of the Oren pieces had a black tone, and their coptisine chloride content was as low as 37–91% compared with normal‐tone pieces. As a result of heat‐processing crude Oren at 160°C for 150 min in a constant‐temperature oven, the coptisine chloride content decreased to 25.6%. Furthermore, the coptisine chloride content decreased to about 70% when heating heat‐processed Oren for 3 min with an open flame, and the color changed to a dark brown. Conclusion Our results suggest that black‐colored chopped Oren pieces in the market are produced by excessive heating, which affects the quality of the medicine and its alkaloid content.