Investigation of drying with ultrasonic pretreatment on the chemical composition of the essential oil from Cyperus rotundus L. tubers

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Abstract
Drying is an important step, as it extends plant durability and delays the development of undesirable microorganisms. However, depending on the drying method, conditions involved and plant species, changes can occur in the plants, which can improve or reduce their medicinal properties. Ultrasonic pretreatment has the advantage of facilitating water migration into the cells, improving the drying rate. In this context, the objective of this study was to evaluate the influence of different drying temperatures associated with ultrasonic pretreatment, on the chemical composition of the essential oil from Cyperus rotundus L. tubers. The assays were conducted according to a Central Composite Rotational Design (CCRD), considering two factors with the following ranges: duration of the ultrasonic bath from 0 to 40 minutes, drying air temperature from 40 to 70 ºC. The essential oil was extracted by hydrodistillation and its constituents were identified by gas chromatography coupled to mass spectrometry (GC–MS). Twenty-four compounds were identified in C. rotundus essential oil, corresponding to more than 70% of the total peak areas resulting from the chromatographic reading. In the twelve drying treatments evaluated, the compounds 3,4-dimethyl-3-cyclohexen-1-carboxaldehyde, caryophyllene oxide and α-cyperone were found at higher concentrations (between 17.85-25.38%; 17.27-25.26%; 4.95-11.34%, respectively) in eleven; in treatment 11, the major compounds were caryophyllene oxide (23.40%), 3,4-dimethyl-3-cyclohexen-1-carboxaldehyde (21.5%) and humulene (8.41%). At high temperatures and long ultrasonic times, a lower quality of C. rotundus essential oil was observed. The best results were obtained at intermediate ultrasonic bath temperatures and times, where there was an improvement in quality compared to fresh tubers (control).

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