Purification of Rosmarinic Acid from Rosemary Extract and the Evaluation of the Antibacterial and Antioxidant Effects of Rosmarinic Acid and Its Derivatives

Rosmarinic acid (RA), a natural polyphenolic hydroxyl compound found from plants, exhibits many biological activities. This study reported an efficient purification method for RA from the water-soluble rosemary extract. By employing silica gel column chromatography combined with liquid–liquid extraction, the water-soluble extract of rosemary was refined to yield RA with a purity of 92.85 ± 3.18%. To further enhance the potential of RA as a natural preservative, the prepared RA was esterified to produce methyl rosmarinate (RA-me) and propyl rosmarinate (RA-pro). The antioxidant and antibacterial activities of RA and its derivatives were subsequently evaluated. The results indicated that RA and its esterified derivatives exhibited more pronounced antibacterial efficacy against the Gram-positive bacteria than Gram-negative bacteria. Moreover, the antibacterial activity of the ester derivatives was enhanced compared to that of RA. RA and RA-me exhibited comparable antioxidant activity, which was superior to that of RA-pro. In summary, this study established an effective purification strategy for RA, laying a foundation for developing better natural, non-toxic preservatives with antibacterial activity.