Effect of Freezing and Drying on the Yield and Chemical Composition of Essential Oil of Rosemary (Rosmarinus officinalis L.)

This work aimed to evaluate three post-harvest processes on chemical composition and yield of rosemary (Rosmarinus officinalis L.) essential oil. Leaves were collected at 8 h 30 min in Jaguariuna, Sao Paulo State, Brazil. They were divided into three batches. The first batch was immediately submitted to hydrodistillation in order to know its initial volatile composition. The remaining batches were submitted to two different treatments. At one of these batches, the leaves were dried in a forced-air drier (35 degrees C/3 days). At the last treatment, leaves were placed in sealed, air-tight plastic food bags and stored at -20 +/- 0.5 degrees C for two weeks. Essential oils were obtained by hydrodistillation in a Clevenger-type apparatus for 2 h 30 min and analyzed by GC-MS (Shimadzu, QP-5050, with DB-5-capillary column: 30 m x 0,25 mm x 0,25 mu m). Carrier gas was helium (1.7 ml/min); split ratio: 1:20. Temperature program: 60 degrees C, rising to 240 degrees C at 3 degrees C/min. Injector temperature: 240 degrees C and detector temperature: 260 degrees C. Identifications of chemical compounds were made by matching their mass spectra and Kovat's indices (IK) values with known compounds reported in the literature. The data of yield and chemical composition were submitted to ANOVA, followed by Tukey's test. The highest essential oil concentrations were observed in frozen samples (0.94%-a), followed by dried samples (0.92%-b). Essential oil from fresh-material presented smaller yield (0.81%-c). Comparison of the essential oil profiles showed no statistically significant differences in camphor content (fresh-26.9%-a; dried-26.9%-a; frozen-25.7%-a), major component. The compounds 1.8 cineole (fresh-19.9%-a; dried-18.5%-a; frozen-14.4%-b) and myrcene (fresh-15.9%-a; dried-15.7%-a; frozen-11.9%-b) showed highest content in fresh and dried samples. a-pineno (fresh-14.4%-b; dried-13.8%-b; frozen-16.6%-a), camphene (fresh-4.0%-b; dried-4.3%-b; frozen-5.1%-a) and a-limonene (fresh-3.9%-b; dried-4.1%-b; frozen-4.9%-a) presented highest content when submitted to freezing. These results showed that the freezing process increased the yield of rosemary essential oil, but changed its composition, but, for some aromatic species, a proportion of the oil yield must be sacrificed to ensure the required essential oil quality.