Development of a green procedure of citrus fruits waste processing to recover carotenoids

In this study, an original and green procedure of processing waste of the citrus fruits was developed using the concept of bio-refinery, innovative techniques “ultrasound” and “micro-wave”, and a green solvent “limonene” to recover carotenoids. Essential oil extraction was performed by Solvent Free Microwave Extraction (SFME) and compared to steam distillation (SD). The essential oil yields were comparable for both processes: 4.02 ± 0.23% for SFME and 4.16 ± 0.05% for SD. After that, carotenoid extraction from citrus peels was performed by ultrasound-assisted extraction (UAE) and conventional extraction (CE) using d-limonene obtained starting from essential oil, as a solvent, and then compared to n-hexane extract. 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, temperature and time were 208 W cm⁻², 20 °C and 5 min giving carotenoid content of 11.25 mg L⁻¹. Compared to the conventional extraction, (UAE) gave an increase of 40% in carotenoid content. The comparison to n-hexane extract gave no significant changes in carotenoid content. Combination of microwave, ultrasound and d-limonene obtained from a bio-refinery of a by-product of citrus fruits industry allow us to develop a very good environmental green approach giving high added values compounds, with a saving of time, and a complete valorisation of waste.