The yield, chemical profile and antioxidant activity of sage (Salvia officinalis L.) essential oils (SEOs) isolated from shaded (pearl-, red- and blue-colored nets) or non-shaded plants from three different harvest-time phenological stages (May, August and September) investigated. Both main effects and their interactions were highly significant (p < 0.01). Blue nets produced the highest yield in the first (4.09 mL/100 g) and second (3.29 mL/100 g) harvests, significantly exceeding all other treatments within the same harvest period. In the third harvest, unshaded control plants achieved the highest yield (3.55 mL/100 g). The total number of individual SEO components varied depending on the harvest time and shading treatment (27–35). The most abundant components were thujone (cis-thujone, 24.1–36.1%; trans-thujone, 4.9–13.1%) camphor (20.0–30.2%) and 1,8-Cineole (8–11%). The content of undesirable component camphor was the lowest in all three harvests in plants covered with blue shading nets. FRAP values ranged from 0.462 mg Fe2+/g oil (second harvest, red net) to 1.151 mg Fe2+/g oil (first harvest, red net), while EC50 values ranged from 9.169 mg/mL (first harvest, red net) to 37.004 mg/mL (third harvest, blue net). The third-harvest blue-net sample exhibited one of the highest FRAP values (1.123 mg Fe2+/g oil) yet the weakest DPPH radical scavenging activity (EC50 = 37.004 mg/mL), reflecting different mechanisms of antioxidant action between the two assays. In conclusion, the highest yield and best quality of EO were achieved in the first harvest. Shading the plants, particularly with blue nets, contributed to an increase in EO yield, as well as improved EO quality, including higher thujone content and lower content of undesirable camphor. Covering the plants with blue nets during the first and second harvest periods enhanced essential oil yield and quality. In the third harvest, open-field conditions favored a higher yield; however, blue-net shading produced the lowest camphor content (20.3%), which may be advantageous for pharmaceutical applications. The choice of whether to maintain or remove nets during the third harvest should therefore be guided by the intended end use of the essential oil.
Milenković et al. (2026) studied this question.