Novel configurations for a citrus waste based biorefinery: from solventless to simultaneous ultrasound and microwave assisted extraction

Innovative extraction configurations for the biorefining of a biomass waste (citrus peel) were developed in this work. Nonconventional energies, such as microwaves (MW) and ultrasounds (US), were directly irradiated to the fresh orange peel using a versatile MW coaxial dipole antenna. This particular MW configuration enabled us to build two new extraction systems: 1) a coaxial solventless MW-assisted extraction approach (SMWAE) and, 2) a simultaneous ultrasound coaxial MW-assisted hydrodistillation (US-MWHD). The yield and chemical composition of the essential oils of the orange peel obtained by the two innovative approaches were analyzed as a function of the extraction time and compared with the coaxial microwave hydrodistillation (MWHD) and conventional hydrodistillation (CH). The EOs were chemically characterized by GC and GC-MS analysis. The residue mash was then used to extract pectin by a MW-assisted procedure. Structure and thermal stability of the pectin were investigated by FTIR and TG. The biorefining of EOs and pectin from a citrus waste maximise the benefits of our proposed green methodologies, which involve safe operability, faster processing and easy scalability. Furthermore, the energy consumed per unit mass of products in each step of the orange peel biorefining clearly showed that the most promising approach is the SMWAE (since it is around around 27 times lower than the CH approach). The MWHD and US-MWHD also showed more than 60% energy savings compared to the CH.