In-sample stability of phenolic abietane diterpenes: A case of Salvia apiana Jeps.

The objective of the study was to improve the stability of phenolic abietanes, including 16-hydroxycarnosic acid, carnosic acid, and carnosol, in extracts from white sage ( Salvia apiana Jeps.). The extracts were prepared using methanol or dichloromethane in a protective environment (amber light, room temperature), which preserved diterpenes during sample preparation but failed to prevent their subsequent degradation, despite the use of dimethylsulfoxide as an aprotic storage solvent. In methanolic extracts, the levels of carnosic acid and 16-hydroxycarnosic acid dropped to 69 % and 77 % of the original value, respectively, after 48 h, and eventually reached 9 % and 17 % of the initial concentration over the course of 3 weeks. Dichloromethane extracts provided higher stability of carnosic acid and 16-hydroxycarnosic acid than methanolic ones, but degradation was still noticeable (33 % and 46 % of the initial concentration, respectively, after 21 day storage at room temperature). Sample freezing at −20°C noticeably slowed degradation, but alone could not prevent it completely: in methanolic extract, the levels of carnosic acid and 16-hydroxycarnosic acids dropped to 79 % and 87 % after 21 days of storage. The use of ascorbic acid as a protectant effectively stopped the degradation of diterpenes in samples kept at room temperature for 3 weeks, whereas butylated hydroxytoluene proved to be ineffective as protectant. Due to its simplicity, the proposed sample stabilization method can be easily adjusted to other raw materials, including economically important plants such as rosemary and common sage. • Protective environment prevents degradation of white sage diterpenes during extraction. • Fast degradation of diterpenes, observed at room temperature, can be slowed by sample freezing. • Methanol and dichloromethane extracts from white sage show different diterpene degradation rates. • Ascorbic acid prevents degradation of diterpenes in extracts stored for 3 weeks at room temperature. • 16-hydroxycarnosic acid and carnosic acid are major phenolic secondary metabolites of white sage.