Characterization and antioxidant properties of polysaccharides extracted from leaves of Salvia rosmarinus Spenn

Salvia rosmarinus Spenn. (rosemary) is a worldwide known aromatic plant, commonly used in culinary and medicine for various healing effects due to lower molecular weight compounds, such as phenols and flavonoids. In this study, we report the isolation, chemical composition and structural properties of macromolecular components composed of polysaccharides, proteins and phenolics. Polymers were obtained from the leaves of the medicinal plant rosemary by sequential extraction with cold water, ammonium oxalate, 1 M and 4 M KOH solutions. Individual fractions differed in the content of carbohydrates, proteins and phenolics. It was found that the highest yield of all fractions was achieved with ammonium oxalate, while the 4 M KOH fraction showed the highest molecular weight. Based on the composition, it is evident that arabinogalactan is the main component of both the aqueous and 1 M KOH fractions, esterified pectin with arabinogalactan from the oxalate fraction, and hemicelluloses (xylan-related polymers) with low arabinogalactan content were identified in the 4 M KOH fraction. The DPPH radical scavenging activity assay revealed a significant effect of rosemary fractions. The aqueous and 1 M KOH fractions achieved antioxidant activity comparable to vitamin C at a concentration of 0.05 and 0.1 mg/mL, respectively, while the oxalate and 4 M KOH fractions reached maximum activity at tenfold higher concentrations.