The study & development of an integrated & additive-free waste orange peel biorefinery

The overall aim of this thesis is to demonstrate how food supply chain waste (FSCW) could be used as a renewable feedstock for a product-focused biorefinery. The volumes of FSCW produced as a result of common food processing operations have been estimated using a new methodology. The latter is based on sold manufactured goods published every year by the European Union (PRODCOM) and highlights the geographical waste hot spots for common food processing operations. The use of this methodology led to the selection of waste orange peel (WOP) as a raw material for the design of an integrated biorefinery. A SWOT analysis was carried out to analyse the opportunity for the design of a WOP valorisation process aimed at the extraction of a maximum of the chemical components, while avoiding the use of acid, additives or pretreatment. The successful development of a microwave biorefinery process centred on the valorisation of WOP was designed based on the integration of microwave assisted D-limonene extraction and a low temperature hydrothermal extraction of pectin.
The work carried-out using microwave hydrothermal treatment proved that pectin can be extracted between 100 and 150 °C under acid-less conditions on a 100 mL scale. A competitive molecular weight distribution was obtained for pectin produced at a temperature of 110 and 120 °C using WOP from which D-limonene, flavonoids and sugar had been previously extracted. A CPMAS 13C-NMR technique was developed to determine the degree of esterification of pectin. D-limonene was extracted under microwave-assisted solvent-less conditions. The optimised conditions studied led to a yield of 1.09 ± 0.18% food grade D-limonene with a high reproducibility on a 1 L scale (500 mbars). Finally, the process used also allowed for the isolation and characterisation of flavonoids and monosaccharides. Following ethanol extraction, a mixture of polymethoxy flavonoids (tetra-O-methyl scutellarein, tangeritin, nobiletin and heptamethoxyflavone), hesperidin and sugar monosaccharides were obtained with yields of 5.87%, 0.24% and 18.35% respectively on a wet basis. The later fraction was composed of 74.21% glucose and 25.35% fructose, as determined by quantitative 13C NMR, showing the potential for this fraction as a fermentation feedstock.