Thermal and mechanical intensification of essential oil extraction from orange peel via instant autovaporization

Citrus peels have a structure permeability preventing an easy essential oil (EO) removal. Extraction of citrus EO performed by hydrodistillation (HD) usually need to be ground beforehand. Hence, we first compared and modeled a 4 h HD on orange peel, ground and in pieces. Significant differences in terms of EO extraction yields were obtained: 1.628 g/100 g dry material (dm) for ground orange peel compared to 0.197 g/100 g dm for orange peels left in pieces. By modeling the EO extraction, the starting accessibility ratio, illustrating the percentage of EO immediately "washed" away by the solvent/surface interaction, was above 50% for the ground product. That is, mechanical and thermal processes need to be combined for this particular material. Therefore, we opted to perform the EO extraction via instant controlled pressure drop (DIC) technology. DIC extraction process is a thermo-mechanical treatment enabling the extraction of EO via autovaporization, followed by a condensation step. After each DIC experimental design treatment, orange peel solid residues were analyzed through solid-phase microextraction (SPME) to determine the amount of EO remaining. DIC treatment was studied on a statistical basis varying two parameters, the number of cycles and total heating time respectively illustrating thermal and mechanical aspects. EO extraction efficiency was determined as the main response parameter. DIC parameters were optimized via statistical answer taking into account the energy consumption resulting with an EO yield of 1.66 +/- 0.045 g/100 g dm. EO extraction via HD and DIC optimized conditions were analyzed with gas chromatography. An examination of the solid structure was achieved with scanning electron microscopy (SEM), which showed a very important expansion of the structure after DIC treatment while HD generated a collapsed and shrunk structure. (C) 2013 Elsevier B.V. All rights reserved.