Seasonal variation in essential oil composition, oil toxicity and the biological activity of solvent extracts of three South African Salvia species

Aromatic plants contain both volatile and non-volatile fractions and the chemical composition of these two fractions may be influenced by seasonal changes. The essential oil and solvent extracts of S. africana-caerulea, S. africana-lutea and S. lanceolata, collected at the same locality throughout the 2005 growing season, were compared in terms of essential oil composition, yields and biological activities. Mostly quantitative, rather than qualitative variation was observed in the oil composition of each species. Major fluctuations in the composition of S. africana-caerulea oil included limonene (2-33%) and viridiflorol (2-24%). Levels of α-pinene (1-12%), myrcene (2-12%) and α-eusdesmol (trace-13%) fluctuated seasonally in the S. africana-lutea oil. In S. lanceolata, considerable changes were noted for β-caryophyllene (1-19%), β-caryophyllene oxide (1-21%) and ledol (3-12%). The extract prepared from S. lanceolata harvested in winter was more active against Gram-positive bacteria. The S. africana-caerulea extract exhibited the most favourable anti-plasmodial activity when harvested in winter (IC50 value: 12 μg ml− 1), which contrasts with the lowest anti-plasmodial activity of S. lanceolata obtained at the same period (IC50 value: 43 μg ml− 1). The anti-oxidant activity of the solvent extracts also displayed variation over seasons with the winter collection of S. africana-lutea yielding the most favourable anti-oxidant activity (IC50 value: 10 μg ml− 1). All the solvent extracts prepared from the winter collection exhibited the lowest toxicity (20 < IC50 values < 60 μg ml− 1), while the three essential oils obtained from autumn collection were more toxic (0.03 < IC50 values < 0.4 μg ml− 1).