Preliminary screening for extraction techniques and bioactive fraction of Coptidis Rhizoma based on microcalorimetry

摘要

Context: Extraction techniques may alter the antibacterial activity of Coptidis Rhizoma (C. Rhizoma), which is regarded as characteristic of this herb. Objective: To explore the best extraction techniques of C. Rhizoma and the fraction(s) with the strongest antibacterial activity. Methods: Using microcalorimetry, the influence of different extraction fractions of C. Rhizoma obtained by decoction, reflux, and ultrasound techniques on Escherichia coli growth was investigated by analyzing the power–time curves and some thermokinetic parameters. Then the antibacterial activities of each fraction of C. Rhizoma were compared by analysis of variance (ANOVA). Meanwhile, the minimum inhibitory concentration (MIC) of the strongest antibacterial fraction was determined by 2-fold dilution method. Results and conclusion: The petroleum ether (PE), chloroform (CHCl₃), ethyl acetate (EtOAc), and n-butyl alcohol (n-BuOH) fraction, water extract, and the residue after extraction all inhibited the growth of E. coli. The potency of the inhibitory effects was as follows: n-BuOH fraction EtOAc fraction CHCl₃ fraction PE fraction residue after extraction water extract. The decoction technique was regarded as the optimum extraction technique. The n-BuOH fraction from the decoction technique was observed to have the strongest antibacterial fraction with half-inhibitory concentration IC₅₀ of 1.68?mg/mL and MIC of 200 μg/mL.