In-Depth Characterisation and Microwave-Assisted Conversion of Opuntia ficus-indica into High-Value-Added Platform Compounds

Nowadays, humanity is facing a paradigm change in the productive model, switching from fossil-based carbon sources and a linear economy, to more sustainable and circular alternatives. In this regard, lignocellulosic biomass is considered as a perfect substitute for fossil-based carbon sources. Opuntia ficus-indica (OFI) is a crassulacean acid metabolism species, capable of growing in arid places that are not suitable for food production. In this work, a systematic fractionation process combined with analytical techniques (nuclear magnetic resonance, thermogravimetric analysis, and Fourier-transform infrared spectroscopy) unveiled the extraordinarily high carbohydrate content of OFI fruit. Therefore, OFI fruit is a perfect feedstock for the obtention of high-value-added chemicals, namely levulinic acid (LA) and 5-hydroxymethylfurfural (5-HMF). By microwave-assisted thermochemical treatment of the most suitable fraction, LA was obtained in a 22.1 wt. % yield in an aqueous monophasic system, and 5-HMF in an 11.5 wt. % yield in a biphasic system. Reuse of the catalyst and co-catalyst in a monophasic system led to 5-HMF in a 14.3 wt. % yield after five cycles, avoiding the need for an organic co-solvent. This work demonstrates the potential of this feedstock to obtain high-value-added chemicals, employing marginal land in environments where other crops are unable to grow.