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AbstractIn order to increase the yield of essential oils in hydrodistillation of bay laurel and sage, the effect of pretreatment with ultrasound and enzymes (under different conditions of xylanase pretreatment) was studied. The effects of the optimized conditions (concentration of xylanase 0.20 mg/mL in buffer pH=6.5 at 40°C for 4 h) during the enzymatic pretreatment showed that despite the optimization the activity of xylanase did not significantly affect the quantity and quality of essential oils of bay laurel and sage. Ultrasonic pretreatment prior to enzymatic pretreatment with the addition of optimized xylanase resulted in increased yields of dominant compounds (α-thujone 27.42%, β-thujone 12.15%, and camphor 20.94%) in sage essential oil, while in bay laurel the amount of dominant compounds (1,8-cineole 24.65% and α-terpenyl acetate 11.05%) was not significantly increased. Despite minor changes, ultrasonic and enzymatic pretreatment of the plant materials did not significantly affect the chemical composition of the essential oils of bay laurel and sage compared with the control without pretreatment, as confirmed by the Spearman rank test (p< 0.05). The main advantage of ultrasonic extraction is the reduction in pretreatment time. Ultrasonic pretreatment for only 10 min before enzymatic pretreatment resulted in a 50% increase in sage essential oil yield and a 40% increase in bay laurel essential oil yield.