Ultrasound-assisted emulsification–extraction of orange peel metabolites prior to tentative identification by LC–QTOF MS/MS

An optimized method for extraction and characterization of compounds present in orange peel has been developed. The extraction method allows the simultaneous extraction of polar and non-polar compounds by using two immiscible extractants (a polar extractant—an 80:20 (v/v) methanol–water mixture, and a non-polar extractant—n-hexane). The method is ultrasound-assisted, thus facilitating both formation of a stable emulsion between the two immiscible extractants and favoring mass-transfer from the solid sample to the liquid phases by a wide contact surface. Optimization of the ultrasound-assisted emulsification–extraction (USAEE) led to the following values as desirability conditions for both extracts: 32% amplitude, 0.75s/s duty cycle and 7.5min of extraction time. The extracts obtained under these conditions were analyzed by LC–QTOF MS/MS in positive and negative ionization modes. Tentative identification of the most significant compounds present in each extract allowed their characterization by using high resolution tandem mass spectrometry. The optimum extracts provided by USAEE were compared by using Principal Component Analysis to those obtained by conventional extraction based on maceration. Thus, the composition of the polar extracts obtained after 7.5min ultrasonication was similar to that of conventional maceration for 4h in both the ionization modes. On the contrary, the analysis of non-polar extracts led to different results depending on the ionization mode: the ultrasound-assisted extract was similar to those of conventional maceration for 10h in negative and positive ionization. This behavior could be explained by the contribution of different groups of compounds to each ionization mode.