An analytical method for measuring rosmarinic acid (RA) and luteolin (Lut), the major polyphenolic substances in Perilla frutescens Britton (Labiatae) was established. High-performance liquid chromatography was used to determine the concentration of RA in perilla leaf solutions prepared by two successive extractions with water-acetone-hydrochloric acid (20:80:1, v/v/v). The concentration of Lut in solutions prepared by two successive extractions with ethanol-hydrochloric acid (100:1, v/v) was determined by liquid chromatography-mass spectrometry. The mean concentrations of RA and Lut in the same samples of perilla leaves were 3.95 ± 0.42 and 0.039 ± 0.004 mg·g-1, respectively, with the concentration of RA being 100 times greater than that of Lut. It was also demonstrated that there were seasonal changes in the RA concentration of perilla leaves collected from the same field and that RA levels varied between different growing areas.
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