Bio-refinery of orange peels waste: a new concept based on integrated green and solvent free extraction processes using ultrasound and microwave techniques to obtain essential oil, polyphenols and pectin.

In this study, extraction of essential oil, polyphenols and pectin from orange peel has been optimized using microwave and ultrasound technology without adding any solvent but only "in situ" water which was recycled and used as solvent. The essential oil extraction performed by Microwave Hydrodiffusion and Gravity (MHG) was optimized and compared to steam distillation extraction (SD). No significant changes in yield were noticed: 4.22 ± 0.03% and 4.16 ± 0.05% for MHG and SD, respectively. After extraction of essential oil, residual water of plant obtained after MHG extraction was used as solvent for polyphenols and pectin extraction from MHG residues. Polyphenols extraction was performed by ultrasound-assisted extraction (UAE) and conventional extraction (CE). Response surface methodology (RSM) using central composite designs (CCD) approach was launched to investigate the influence of process variables on the ultrasound-assisted extraction (UAE). The statistical analysis revealed that the optimized conditions of ultrasound power and temperature were 0.956 W/cm(2) and 59.83°C giving a polyphenol yield of 50.02 mgGA/100 g dm. Compared with the conventional extraction (CE), the UAE gave an increase of 30% in TPC yield. Pectin was extracted by conventional and microwave assisted extraction. This technique gives a maximal yield of 24.2% for microwave power of 500 W in only 3 min whereas conventional extraction gives 18.32% in 120 min. Combination of microwave, ultrasound and the recycled "in situ" water of citrus peels allow us to obtain high added values compounds in shorter time and managed to make a closed loop using only natural resources provided by the plant which makes the whole process intensified in term of time and energy saving, cleanliness and reduced waste water.

Improved microwave steam distillation apparatus for isolation of essential oils. Comparison with conventional steam distillation.

Steam distillation (SD) is routinely used by analysts for the isolation of essential oils from herbs, flowers and spices prior to gas chromatographic analysis. In this work, a new process design and operation for an improved microwave steam distillation (MSD) of essential oils from aromatic natural products was developed. To demonstrate its feasibility, MSD was compared with the conventional technique, SD, for the analysis of volatile compounds from dry lavender flowers (Lavandula angustifolia Mill., Lamiaceae). Essential oils isolated by MSD were quantitatively (yield) and qualitatively (aromatic profile) similar to those obtained by SD, but MSD was better than SD in terms of rapidity (6 min versus 30 min for lavender flowers), thereby allowing substantial savings of costs in terms of time and energy. Lavender flowers treated by MSD and SD were observed by scanning electron microscopy. Micrographs provide evidence of more rapid opening of essential oil glands treated by MSD, in contrast to conventional SD.