Moderate electric field-assisted hydro-distillation of thyme essential oil: Characterization of microstructural changes

Abstract

Novel technologies are applied to improve the hydro-distillation process in the production of essential oils of commercial importance. In this study, it was aimed to examine the effect of the moderate electric field-assisted hydro-distillation (MEF-D) method, which was applied at different frequencies and wave type conditions, on the microstructural changes of thyme samples. Microscopic images of the samples were taken before and after MEF-D treatments. The perimeter and area of peltate and capitate cells in leaves and stems were measured, and the percentage of damage to secretory cells was determined. The results were compared with the conventional hydro-distillation method. The correlation analysis was performed for the relations between different responses; image analysis results, the cell disintegration index (Zc), and essential oil yields after MEF-D treatments. The highest oil yield (52.2 ± 4.02) was obtained with MEF-D square wave type at 1,000 Hz condition (p < 0.05). Glandular trichomes were damaged in all conditions (p < 0.05). Damaged Glandular Trichomes (DGT) values were higher for MEF-D square wave conditions compared to the sine wave (p < 0.05). The highest Zc values (0.80 ± 0.02 for sine wave type and 0.78 ± 0.03 for square wave type) were obtained for 1,000 Hz frequency application in both wave types. Good correlations (Pearson correlation coefficient > 0.995) between image analysis parameters and Zc were obtained. MEF-D method increased the anatomical changes, and thus resulted in a higher yield of essential oil. It is expected that the results of the study will contribute to the improvement of hyro-distillation processes.